Indexing glomerular filtration rate for body surface area in obese patients is misleading: concept and example

A molecular morphometric approach to diabetic kidney disease can link structure to function and outcome

Diabetic kidney disease is the leading cause of kidney failure. However, studies of molecular mechanisms of early kidney damage are lacking. Here we examined for possible linkage between transcriptional regulation and quantitative structural damage in early diabetic kidney disease in Pima Indians with type 2 diabetes. Tissue obtained from protocol kidney biopsies underwent genome-wide compartment-specific gene expression profiling and quantitative morphometric analysis. The ultrastructural lesion most strongly associated with transcriptional regulation was cortical interstitial fractional volume (VvInt), an index of tubule-interstitial damage. Transcriptional co-expression network analysis identified 1843 transcripts that correlated significantly with VvInt. These transcripts were enriched for pathways associated with mitochondrial dysfunction, inflammation, migratory mechanisms, and tubular metabolic functions. Pathway network analysis identified IL-1β as a key upstream regulator of the inflammatory response and five transcription factors cooperating with p53 to regulate metabolic functions. VvInt-associated transcripts showed significant correlation with the urine albumin to creatinine ratio and measured glomerular filtration rate 10 years after biopsy, establishing a link between the early molecular events and long-term disease progression. Thus, molecular mechanisms active early in diabetic kidney disease were revealed by correlating intrarenal transcripts with quantitative morphometry and long-term outcomes. This provides a starting point for identification of urgently needed therapeutic targets and non-invasive biomarkers of early diabetic kidney disease.

Association of Serum Amyloid A with Kidney Outcomes and All-Cause Mortality in American Indians with Type 2 Diabetes

BACKGROUND

Serum amyloid A (SAA) induces inflammation and apoptosis in kidney cells and is found to be causing the pathologic changes that are associated with diabetic kidney disease (DKD). Higher serum SAA concentrations were previously associated with increased risk of end-stage renal disease (ESRD) and death in persons with type 2 diabetes and advanced DKD. We explored the prognostic value of SAA in American Indians with type 2 diabetes without DKD or with early DKD.

METHODS

SAA concentration was measured in serum samples obtained at the start of follow-up. Multivariate proportional hazards models were employed to examine the magnitude of the risk of ESRD or death across tertiles of SAA concentration after adjustment for traditional risk factors. The C statistic was used to assess the additional predictive value of SAA relative to traditional risk factors.

RESULTS

Of 256 participants (mean ± SD glomerular filtration rate [iothalamate] = 148 ± 45 mL/min, and median [interquartile range] urine albumin/creatinine = 39 [14-221] mg/g), 76 developed ESRD and 125 died during a median follow-up period of 15.2 and 15.7 years, respectively. After multivariable proportional hazards regression, participants in the 2 highest SAA tertiles together exhibited a 53% lower risk of ESRD (hazard ratio [HR] 0.47, 95% CI 0.29-0.78), and a 30% lower risk of death (HR 0.70, 95% CI 0.48-1.02), compared with participants in the lowest SAA tertile, although the lower risk of death was not statistically significant. Addition of SAA to the ESRD model increased the C statistic from 0.814 to 0.815 (p = 0.005).

CONCLUSIONS

Higher circulating SAA concentration is associated with a reduced risk of ESRD in American Indians with type 2 diabetes.

Determinants of glomerular filtration rate following bariatric surgery in individuals with severe, otherwise uncomplicated, obesity: an observational, prospective study

AIMS

Obesity-induced nephropathy is an established clinical entity arising from a "maladaptive" response to lipid accumulation at the nephron level. Bariatric surgery positively affects renal function, reducing or increasing glomerular filtration rate (GFR) in subjects with hyperfiltration and renal impairment, respectively. The effect of this surgery in patients with normal estimated GFR (eGFR) is less clear.

METHODS

A complete clinical and biochemical assessment of 135 severely obese, otherwise healthy subjects, was obtained before Roux-en-Y gastric bypass (RYGB). All subjects underwent an OGTT with plasma glucose and insulin determinations. Follow-up data were recorded at 6, 12, 24 and 48 months after intervention.

RESULTS

Baseline eGFR was 98.2 ± 13.6 ml/min/1.73 m²; hyperfiltration (>120 ml/min/1.73 m²) was present in 7% of the cohort. No eGFR variation over the follow-up emerged, except at the last visit (-3.6 ± 1.4 ml/min/1.73 m² at month 48, p = 0.01 vs baseline). In the univariate analysis, the renal performance at 48 months was inversely related to baseline eGFR (r = -0.17, p = 0.04) and plasma triglycerides (r = -0.04, p = 0.05). Fasting and OGTT-derived variables did not impact eGFR. By multiple regression analysis, eGFR time course was independently predicted only by baseline eGFR (p = 0.03). Interestingly, patients having a baseline eGFR >100 ml/min/1.73 m² (median value) showed, after 48 months, an average loss of -8.3 ± 2.2 ml/min/1.73 m², while those with eGFR <100 exhibited a slight increase (+1.8 ± 2.3 ml/min/1.73 m², p < 0.01).

CONCLUSIONS

Long-term data confirm the safety of RYGB on renal function. Interestingly, a subtle hyperfiltration, i.e., occurring in high-normal range of eGFR, is attenuated by surgical procedure. Lastly, high serum triglycerides may track an unfavorable renal outcome.

Effect of large weight reductions on measured and estimated kidney function

BACKGROUND

When patients experience large weight loss, muscle mass may be affected followed by changes in plasma creatinine (pCr). The MDRD and CKD-EPI equations for estimated GFR (eGFR) include pCr. We hypothesised that a large weight loss reduces muscle mass and pCr causing increase in eGFR (creatinine-based equations), whereas measured GFR (mGFR) and cystatin C-based eGFR would be unaffected if adjusted for body surface area.

METHODS

Prospective, intervention study including 19 patients. All attended a baseline visit before gastric bypass surgery followed by a visit six months post-surgery. mGFR was assessed during four hours plasma 51Cr-EDTA clearance. GFR was estimated by four equations (MDRD, CKD-EPI-pCr, CKD-EPI-cysC and CKD-EPI-pCr-cysC). DXA-scans were performed at baseline and six months post-surgery to measure changes in lean limb mass, as a surrogate for muscle mass.

RESULTS

Patients were (mean ± SD) 40.0 ± 9.3 years, 14 (74%) were female and 5 (26%) had type 2 diabetes, baseline weight was 128 ± 19 kg, body mass index 41 ± 6 kg/m2 and absolute mGFR 122 ± 24 ml/min. Six months post-surgery weight loss was 27 (95% CI: 23; 30) kg, mGFR decreased by 9 (-17; -2) from 122 ± 24 to 113 ± 21 ml/min (p = 0.024), but corrected for current body surface area (BSA) mGFR was unchanged by 2 (-5; 9) ml/min/1.73 m2 (p = 0.52). CKD-EPI-pCr increased by 12 (6; 17) and MDRD by 13 (8; 18) (p < 0.001 for both), while CKD-EPI-cysC was unchanged by 2 (-8; 4) ml/min/1.73 m2 (p = 0.51). Lean limb mass was reduced by 3.5 (-4.4;-2.6; p < 0.001) kg and change in lean limb mass correlated with change in plasma creatinine (R 2 = 0.28, p = 0.032).

CONCLUSIONS

Major weight reductions are associated with a reduction in absolute mGFR, which may reflect resolution of glomerular hyperfiltration, while mGFR adjusted for body surface area was unchanged. Estimates of GFR based on creatinine overestimate renal function likely due to changes in muscle mass, whereas cystatin C based estimates are unaffected.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT02138565 . Date of registration: March 24, 2014.

Bariatric Surgery and Kidney-Related Outcomes

The prevalence of severe obesity in both the general and the chronic kidney disease (CKD) populations continues to rise, with more than one-fifth of CKD patients in the United States having a body mass index of ≥35 kg/m². Severe obesity has significant renal consequences, including increased risk of end-stage renal disease (ESRD) and nephrolithiasis. Bariatric surgery represents an effective method for achieving sustained weight loss, and evidence from randomized controlled trials suggests that bariatric surgery is also effective in improving blood pressure, reducing hyperglycemia, and even inducing diabetes remission. There is also observational evidence suggesting that bariatric surgery may diminish the long-term risk of kidney function decline and ESRD. Bariatric surgery appears to be relatively safe in patients with CKD, with postoperative complications only slightly higher than in the general bariatric surgery population. The use of bariatric surgery in patients with CKD might help prevent progression to ESRD or enable selected ESRD patients with severe obesity to become candidates for kidney transplantation. However, there are also renal risks in bariatric surgery, namely, acute kidney injury, nephrolithiasis, and, in rare cases, oxalate nephropathy, particularly in types of surgery involving higher degrees of malabsorption. Although bariatric surgery may improve long-term kidney outcomes, this potential benefit remains unproved and must be balanced with potential adverse events.

Normalization of glomerular filtration rate in obese children

BACKGROUND

Glomerular filtration rate (GFR) is conventionally indexed to body surface area (BSA), but this may lead to biased results when applied to subjects of abnormal body size. The aim of our study was to examine the impact of normalization to the BSA and alternative body size descriptors on measured and estimated GFR in overweight and obese children.

METHODS

This was a cross-sectional study of 313 children aged 8-9 years old. GFR was measured by 24-h creatinine clearance (CrCl) and additionally estimated from serum creatinine and cystatin C (CysC) using the combined Zappitelli formula, both as absolute values and adjusted to various body size descriptors. The results were compared between 163 normal-weight, 89 overweight and 61 obese children.

RESULTS

Compared to the normal-weight children, mean absolute GFR (both measured and estimated) was higher in the overweight and obese children, whereas BSA-adjusted GFR was lower. Linear regression models fitted in normal-weight children revealed equally close associations between absolute GFR and squared height, ideal body weight (IBW) and BSA derived from IBW. Normalization of GFR to the IBW-derived BSA completely eliminated the discrepancy between absolute and BSA-indexed GFR in overweight and obese children.

CONCLUSIONS

Indexing of GFR to BSA calculated from the ideal-rather than actual-body weight is a promising approach to avoid overcorrection when studying obese children. Further studies should assess the accuracy of this approach across the full range of age and BMI distribution.

Removal of body surface area normalisation improves raw-measured glomerular filtration rate estimation by the Chronic Kidney Disease Epidemiology Collaboration equation and drug dosing in the obese

BACKGROUND/AIM

We aimed to compared estimated glomerular filtration rate (eGFR) according to the Chronic Kidney Disease Epidemiology Collaboration equation (CKD-EPI), with (mL/min/1.73 m(2) ) and without body surface area (BSA) normalisation (CKD-EPI_noBSA, mL/min) against measured (99m) Technetium - diethylenepentaacetic acid (Tc-DTPA GFR) (mL/min) in 222 individuals, including 80 with malignancy.

METHODS

BSA was calculated for each individual using the Du Bois equation. The CKD-EPI and CKD-EPI_noBSA equations were compared with measured Tc-DTPA GFR with respect to bias, proportion within 30% of GFR (P30) and root mean square error for predicting levels of GFR, and concordance in relation to carboplatin dosing.

RESULTS

The mean (SD) for BSA and measured GFR for the entire group was 1.99 (0.25) m(2) and 127 (41) mL/min respectively. The P30 for Tc-DTPA GFR was significantly higher with the CKD-EPI_noBSA (80%) than with the CKD-EPI equation (63%, P = 0.0001). In those with body mass index (BMI) > 30 kg/m(2) , the P30 values for the CKD-EPI_noBSA and CKD-EPI were 74% and 42% respectively (P < 0.0001). Carboplatin dosing concordance for the cancer patients using the CKD-EPI and CKD-EPI_noBSA equation was 71% and 56% respectively (P = 0.07). In 78 individuals with BMI > 30 kg/m(2) , concordance in relation to carboplatin dosing using CKD-EPI_noBSA was 65% compared with 26% with the CKD-EPI (P < 0.0001).

CONCLUSION

The CKD-EPI without normalisation (CKD-EPI_noBSA) equation was superior to the CKD-EPI equation in estimating raw-measured Tc-DTPA GFR (mL/min).

Structural Predictors of Loss of Renal Function in American Indians with Type 2 Diabetes

BACKGROUND AND OBJECTIVES

Diabetes is the leading cause of kidney failure in the United States, but early structural determinants of renal function loss in type 2 diabetes are poorly defined. We examined the association between morphometrically determined renal structural variables and loss of renal function in 111 American Indians with type 2 diabetes who volunteered for a research kidney biopsy at the end of a 6-year clinical trial designed to test the renoprotective efficacy of losartan versus placebo. Participants were subsequently followed in an observational study, in which annual measurements of GFR (iothalamate) initiated during the clinical trial were continued.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Renal function loss was defined as ≥40% loss of GFR from the research examination performed at the time of kidney biopsy. Associations with renal function loss were evaluated by Cox proportional hazards regression. Hazard ratios (HRs) were reported per 1-SD increment for each morphometric variable.

RESULTS

Of 111 participants (82% women; baseline mean [±SD] age, 46 years old [±10]; diabetes duration, 16 years [±6]; hemoglobin A1c =9.4% [±2.2]; GFR=147 ml/min [±56]; median albumin-to-creatinine ratio, 41 mg/g [interquartile range, 13-158]), 51 (46%) developed renal function loss during a median follow-up of 6.6 years (interquartile range, 3.1-9.0). Fourteen had baseline GFR <90 ml/min, and three had baseline GFR <60 ml/min. Higher mesangial fractional volume (HR, 2.27; 95% confidence interval [95% CI], 1.58 to 3.26), percentage of global glomerular sclerosis (HR, 1.63; 95% CI, 1.21 to 2.21), nonpodocyte cell number per glomerulus (HR, 1.50; 95% CI, 1.10 to 2.05), glomerular basement membrane width (HR, 1.48; 95% CI, 1.05 to 2.08), mean glomerular volume (HR, 1.42; 95% CI, 1.02 to 1.96), and podocyte foot process width (HR, 1.28; 95% CI, 1.03 to 1.60); lower glomerular filtration surface density (HR, 0.62; 95% CI, 0.41 to 0.94); and fewer endothelial fenestrations (HR, 0.68; 95% CI, 0.48 to 0.95) were each associated with GFR decline after adjustment for baseline age, sex, duration of diabetes, hemoglobin A1c, GFR, and treatment assignment during the clinical trial.

CONCLUSIONS

Quantitative measures of glomerular structure predict loss of renal function in type 2 diabetes.

Creatinine-based equations for the adjustment of drug dosage in an obese population

AIM

For drug dosing adaptation, the Kidney Disease: Improving Global Outcomes (KDIGO) guidelines recommend using estimated glomerular filtration rate (eGFR) by the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation, after 'de-indexation' by body surface area (BSA). In pharmacology, the Cockcroft-Gault (CG) equation is still recommended to adapt drug dosage. In the context of obesity, adjusted ideal body weight (AIBW) is sometimes preferred to actual body weight (ABW) for the CG equation. The aim of the present study was to compare the performance of the different GFR-estimating equations, non-indexed or de-indexed by BSA for the purpose of drug-dosage adaptation in obese patients.

METHODS

We analysed data from patients with a body mass index (BMI) higher than 30 kg m(-2) who underwent a GFR measurement. eGFR was calculated using the CKD-EPI and Modification of Diet in Renal Disease (MDRD) equations, de-indexed by BSA, and the CG equation, using either ABW, AIBW or lean body weight (LBW) for the weight variable and compared with measured GFR, expressed in ml min(-1).

RESULTS

In our population of obese patients, use of the AIBW instead of the ABW in the CG equation, markedly improved the overall accuracy of this equation [57% for CGABW and 79% for CGAIBW (P < 0.05)]. For high BMI (over 40 kg m(-2)), the accuracy of the CG equations is no different when using LBW than when using AIBW. The MDRD and CKD-EPI equations de-indexed by the BSA also performed well, with an overall higher accuracy for the MDRD de-indexed equation [(80% and 76%, respectively (P < 0.05)].

CONCLUSIONS

The de-indexed MDRD equation appeared to be the most suitable for estimating the non-indexed GFR for the purpose of drug dosage adaptation in obese patients.

Influence of Weight-Age Normalization on Glomerular Filtration Rate Values of Renal Patients: A STROBE-Compliant Article

To explore whether weight-age (W-A) could be applied in clinical practice, this study was designed to verify the normalization ability of W-A by the data from another medical center, and to access the influence of the normalization on glomerular filtration rate (GFR) values in renal patients.Both plasma clearance (pGFR) and camera-based (gGFR), which were separately scaled to W-A and body surface area (BSA), were measured for patients with diffuse renal diseases. The patients (n = 298) were stratified according to the Chinese body mass index (BMI) criteria and were staged according to the Kidney Disease Outcome Quality Initiatives guideline based on gGFR and pGFR separately.The indices of intraclass correlation coefficient (ICC), concordance correlation coefficient (CCC), and ratio of residual standard deviation to pooled standard deviation (RSD/PSD) suggested that, for all patients and each BMI stratum, W-A was obviously better than BSA in scaling GFR. Both under pGFR or gGFR renal stages, only small amount of the patients encountered stage migrations from BSA to W-A scaled stages. The differences between any 2 of the unscaled, BSA scaled, and W-A scaled gGFR (or pGFR) were not obviously changed. Additionally, in some strata, W-A normalization is better than BSA normalization in decreasing the median bias between pGFR and gGFR.W-A is better than BSA in scaling GFR without obvious modifying GFR values and can be applied in routine clinical practice.

Lean mass modulates glomerular filtration rate in males of normal and extreme body composition

BACKGROUND

Understanding determinants of glomerular filtration rate (GFR) is important in aiding prediction and interpretation of kidney function. Body composition is known to affect GFR but is not included in current screening of kidney disease. We investigated the association between GFR and body composition in healthy young men with differing body mass but without known diabetes or kidney injury.

METHODS

Three groups were recruited: normal BMI (n = 22) with a body mass index (BMI) <25 kg/m(2) , muscular (n = 23) with BMI ≥30 kg/m(2) and bioelectrical impedance body fat ≤20% and obese (n = 22) with BMI ≥30 kg/m(2) and bioelectrical impedance body fat ≥30%. Dietary analyses, GFR clearance by (99m) Tc-DTPA, urine protein and body composition by dual-energy X-ray absorptiometry were measured in all participants. Linear and nonlinear associations of constituents of body composition with GFR were assessed.

RESULTS

Muscular men had a higher GFR (mean 186.4 mL/min; 95% CI 171.7-201.1) than normal BMI and obese groups (P = 0.0007). Urine protein and albumin excretion were not elevated in any participants. On multiple regression analysis (r(2) = 0.60), the variables with strong associations with GFR were age (P = 0.0009) and lean mass (P = 0.0001). Fat mass, protein intake and smoking status were not associated. Skeletal muscle mass correlated significantly with GFR in all subgroups.

CONCLUSION

Age and lean mass were strong determinants of GFR. Estimates of GFR should therefore be indexed to an estimate of lean mass.

The appropriate whole-body index on which to base standardized uptake value in 2-deoxy-2-[(18)F]fludeoxyglucose PET

OBJECTIVE

Tissue uptake of 2-deoxy-2-fluorine-18 fludeoxyglucose ((18)F-FDG) is routinely quantified as standardized uptake value (SUV), which in general is the fraction (F) of administered activity per millilitre of tissue multiplied by an index of body size, usually weight (W), i.e. F/ml × W = SUV or F/ml = SUV × (1/W). Other indices have been suggested as preferable to W, especially lean body mass (LBM) and body surface area (BSA). The second equation mentioned above shows that the reciprocal of the ideal index should correlate closely with F/ml and give a regression line through the origin. The purpose of this study was to determine which of these three indices best meets these criteria.

METHODS

Data were evaluated from 49 males and 51 females undergoing routine (18)F-FDG positron emission tomography/CT. A 3 cm diameter region of interest was drawn over the liver and F/ml recorded. LBM and BSA were estimated from height and weight.

RESULTS

Based on all patients, the reciprocals of the three indices gave similar correlation coefficients with F/ml, but only 1/LBM gave regressions close to the origin. Intercepts were significantly higher for females for 1/W and 1/BSA, consistent with females having more body fat, but there was no significant difference with 1/LBM.

CONCLUSION

LBM is the best index on which to base SUV because adipose tissue accumulates less (18)F-FDG than other soft tissues.

ADVANCES IN KNOWLEDGE

The value of this study lies in its use of a novel, more rational approach than previously to confirm that SUV should be based on LBM.

The effects of weight change on glomerular filtration rate

BACKGROUND

Little is known about the effect of weight loss/gain on kidney function. Analyses are complicated by uncertainty about optimal body surface indexing strategies for measured glomerular filtration rate (mGFR).

METHODS

Using data from the African-American Study of Kidney Disease and Hypertension (AASK), we determined the association of change in weight with three different estimates of change in kidney function: (i) unindexed mGFR estimated by renal clearance of iodine-125-iothalamate, (ii) mGFR indexed to concurrently measured BSA and (iii) GFR estimated from serum creatinine (eGFR). All models were adjusted for baseline weight, time, randomization group and time-varying diuretic use. We also examined whether these relationships were consistent across a number of subgroups, including tertiles of baseline 24-h urine sodium excretion.

RESULTS

In 1094 participants followed over an average of 3.6 years, a 5-kg weight gain was associated with a 1.10 mL/min/1.73 m(2) (95% CI: 0.87 to 1.33; P < 0.001) increase in unindexed mGFR. There was no association between weight change and mGFR indexed for concurrent BSA (per 5 kg weight gain, 0.21; 95% CI: -0.02 to 0.44; P = 0.1) or between weight change and eGFR (-0.09; 95% CI: -0.32 to 0.14; P = 0.4). The effect of weight change on unindexed mGFR was less pronounced in individuals with higher baseline sodium excretion (P = 0.08 for interaction).

CONCLUSION

The association between weight change and kidney function varies depending on the method of assessment. Future clinical trials should examine the effect of intentional weight change on measured GFR or filtration markers robust to changes in muscle mass.

Association between obesity and glomerular hyperfiltration: the confounding effect of smoking and sodium and protein intakes

PURPOSE

Glomerular hyperfiltration has been suggested as a possible mechanism linking obesity and chronic kidney disease (CKD), independently of classical risk factors. We explored the association of overweight and obesity with glomerular hyperfiltration in a large sample of the Swiss adult population, accounting for several confounders including dietary factors.

METHODS

Data from a 2010 to 2012 cross-sectional population-based survey in Switzerland were used. Creatinine clearance (CrCl) was determined from 24-h urine collection; CrCl > 140 ml/min was used to define glomerular hyperfiltration. Participants were categorized into lean (<25 kg/m(2)), overweight (25-29.9 kg/m(2)) and obese (≥30 kg/m(2)) according to body mass index (BMI).

RESULTS

A total of 1339 participants were included in the analysis [median (IQR) age 49.4 (34.3-63.5) years, 48.9 % men]. The prevalences of overweight and obesity were 32.2 and 14.2 %, respectively. Median CrCl was 102[84-121] ml/min in lean, 110 [87-136] ml/min in overweight and 124 [97-150] ml/min in obese participants (p < 0.001). The prevalence of glomerular hyperfiltration increased across BMI categories (10.4, 20.8 and 34.7 %, respectively; p < 0.001). This positive association remained significant after adjusting for age, sex, hypertension, diabetes, smoking and dietary factors (sodium and protein intakes): odds ratio [95 %CI] 2.39 [1.52-3.76] (p < 0.001) for overweight versus lean and 4.10[2.31-7.27] (p < 0.001) for obesity versus lean.

CONCLUSIONS

BMI categories and glomerular hyperfiltration are positively associated, independently of other known CKD risk factors and dietary confounders, suggesting that glomerular hyperfiltration may represent an early renal phenotype in obesity. Our observations confirm the significant association of glomerular hyperfiltration with sodium and protein intakes and identify sodium intake as an important modifying factor of the association between hyperfiltration and obesity.

Long-Term Normal Renal Function after Drastic Weight Reduction in Patients with Obesity-Related Glomerulopathy

AIMS

No long-term studies of renal function evolution in morbidly obese (MO) patients after weight loss are available. The aim of our work was to ascertain the long-term influence of drastic weight reduction on renal function in MO patients with obesity-related glomerular lesions.

METHODS

92 MO patients with normal renal function and biopsy evidence of mild obesity-related glomerulopathy underwent bariatric surgery (BS) and subsequent drastic weight loss. A long-term prospective follow-up (mean duration: 76 ± 42 months) was carried out. Basal renal biopsies and basal and long-term metabolic and renal function studies were performed in all cases. Linear mixed models were applied.

RESULTS

Blood pressure dropped early after BS and remained stable thereafter. Creatinine clearance and BMI fell in the first 2 years, rose slightly after 5 years and then remained stable. Serum creatinine and albuminuria decreased throughout the follow-up period. Renal function and albuminuria evolution showed non-significant differences in relation to the number of glomerular lesions.

CONCLUSIONS

Drastic weight loss in BS-treated MO patients with pre-surgical normal renal function and mild obesity-related glomerular lesions is associated with short- and long-term maintenance of normal renal function and improvement in both arterial hypertension and albuminuria.

Evaluation of the estimated variables for scaling glomerular filtration rate of renal patients: a repeated measures-based method

OBJECTIVE

Using a best variable to scale glomerular filtration rate (GFR) is important for clinical practice. The variables, estimated by equations regressed from a healthy population, are usually used in scaling GFR of renal patients. However, because the predicted variables may deviate in renal patients, it is necessary to verify whether these variables can be used to reduce the variability of GFR of renal patients. This study was designed to use repeated measures analyses to identify the best variable for scaling GFR of renal patients.

METHODS

Patients with non-obstructive renal diseases were enrolled in this study. The absolute GFRs of (99m)Tc-DTPA renography (gGFR) and plasma clearance (pGFR) were measured. The indices relating to between-subjects variability, such as Passing and Bablok regression, intraclass correlation coefficient (ICC) and concordance correlation coefficient (CCC) were used to identify the best variable from body surface area (BSA), extracellular fluid volume (ECV), lean body mass (LBM), total body water (TBW), body mass index (BMI), and metabolic rate (MR).

RESULTS

For the scaled indices related to between-subjects variability, ICC and CCC identified the same ranking sequence (BMI < LBMB(B; Boer) < LBMJ(J; James) < TBW < ECVB(B; Bird) < ECVS(S; Silva) < BSA < MR). In the Passing and Bablok regression, the ratio of residual standard deviation to pooled standard deviation (RSD/PSD) produced the same ranking sequence as that identified by ICC and CCC.

CONCLUSION

The estimated metabolic rate can explain most between-subjects variability of GFR, and seems to be the best variable for scaling GFR of renal patients.

Plasma exogenous creatinine clearance in clinically healthy cats: comparison with urinary exogenous creatinine clearance, tentative reference intervals and indexation to bodyweight

Glomerular filtration rate (GFR) is considered to be the best indicator of overall kidney function. The major objectives of this study were to compare plasma exogenous creatinine clearance (PECC) with a reference method, to establish reference intervals (RIs) for PECC and to assess the effects of indexation of GFR to bodyweight (BW) in cats. PECC was compared with urinary clearance of exogenous creatinine (UECC) in six clinically healthy domestic shorthair cats (experiment 1). Tentative RIs were determined according to current guidelines and the effects of indexation to BW and of covariables on GFR were assessed in 43 clinically healthy cats of various breeds (experiment 2). PECC was 15% higher than UECC (P <0.01), but the two estimates were strongly correlated (r(2)=0.97, P = 0.001). RIs for PECC were 6.4-21.3 mL/min or 1.2-4.9 mL/min/kg. The absolute (i.e. non-indexed) GFR value was not dependent on BW. Thus, indexation of GFR to BW in cats would not standardize the GFR value, but could introduce bias in clinical interpretation. Significant effects of breed, plasma protein concentration and plasma albumin concentration on GFR were demonstrated. Plasma concentrations of urea and creatinine, when assessed separately, were also weakly correlated with GFR in healthy cats. These combined findings contribute to a better understanding of renal function assessment in cats.

Regressing an optimal variable to scale glomerular filtration rate: more variations in glomerular filtration rate are explained

BACKGROUND

To compare glomerular filtration rate (GFR) among individuals, GFR is usually scaled to body surface area (BSA) based on the ratio method, which has been debated for its accuracy in recent years. Reference to the BSA as a normalization standard is the most common method currently in use but has limitations. This study was designed to a better variable to scale GFR.

METHODS

We measured 99mTc- diethylene triamine pentaacetic acid plasma clearance (uncorrected GFR, uGFR) for 322 healthy adults who were enrolled according to the SENIEUR protocol. The individuals were randomly grouped into A and B for regressing and validating the optimal variable, respectively. Nonlinear regression was performed against uGFR, and the selected independent variables were body weight, height, age, and sex.

RESULTS

Among several tested models, the regression coefficients of weight-age formula (W-A) were in narrower 95% confidence interval (CI). The coefficient of determination of the regression line between W-A and uGFR, as an indicator to explain the percentage of variations of GFR, was higher than that of other variables in both groups. The coefficient of determination of the regression line between W-A and uGFR was 0.571, which was higher than that of BSA (0.203) or TBW (0.241).

CONCLUSION

The index variable, based on both body weight and age, has a better statistical relationship to uGFR and is a better variable to scale GFR in adults.

Creatinine or cystatin C - which is a better index of renal function in morbid obesity?

PURPOSE

The most important index of renal function is estimated glomerular filtration rate (eGFR) which can be calculated from creatinine or cystatin C concentration in serum. There is uncertainty, which formula is best suited to assess renal function in morbidly obese patients. The aim of this study was to evaluate eGFR in patients with morbid obesity using formulas: Modification of Diet in Renal Disease (MDRD), Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI), Grubb, Le Bricon, Hoek, Larsson, and to compare the obtained results.

MATERIAL AND METHODS

In 40 morbidly obese patients, serum concentration of cystatin C and creatinine were assayed. Values of eGFR were calculated using the above-mentioned formulas.

RESULTS

The mean value of eGFR ranged from 85.9 to 111.1 ml/min/1.73 m², depending on the formula. The biggest difference between the obtained values was 29% (Grubb vs. Hoek p<0.01). After calculation of eGFR from creatinine concentration (MDRD), 7 patients were qualified to the 2nd and 3rd stage of chronic renal disease, while application of Hoek's formula, based on cystatin C concentration, allotted 27 patients to 2nd and 3rd stage of chronic renal disease. Le Bricon formula gave eGFR values, that correlated best with albuminuria.

CONCLUSION

eGFR calculated using Le Bricon formula based on the cystatin C concentration was significantly lower than eGFR calculated from creatinine concentration and was more closely associated with albuminuria. Relying only on creatinine concentration to estimate glomerular filtration rate can lead to underestimation of renal malfunction in obese patients.

The body composition and excretory burden of lean, obese, and severely obese individuals has implications for the assessment of chronic kidney disease

Obesity could affect associations between creatinine generation, estimated body surface area, and excretory burden, with effects on chronic kidney disease assessment. We therefore examined the impact of obesity on the performances of estimated glomerular filtration rate (eGFR), the urine albumin:creatinine ratio (ACR), and excretory burden in 3611 participants of the Chronic Renal Insufficiency Cohort. Urine creatinine excretion significantly increased with body mass index (BMI) (34 and 31% greater at 40 kg/m(2) or more versus the normal of 18.5-25 kg/m(2)) in men and women, respectively, such that patients with a normal BMI and an ACR of 30 mg/g had the same 24-h albuminuria as severely obese patients with ACR 23 mg/g. The bias of eGFR (referenced to body surface area-indexed iothalamate (i-)GFR) had a U-shaped relationship to obesity in men but progressively increased in women. Nevertheless, obesity-associated body surface area increases were accompanied by a greater absolute (non-indexed) iGFR for a given eGFR, particularly in men. Two men with eGFRs of 45 ml/min per 1.73 m(2), height 1.76 m, and BMI 22 or 45 kg/m(2) had absolute iGFRs of 46 and 62 ml/min, respectively. The excretory burden, assessed as urine urea nitrogen and estimated dietary phosphorus, sodium, and potassium intakes, also increased in obesity. However, obese men had lower odds of anemia, hyperkalemia, and hyperphosphatemia. Thus, for a given ACR and eGFR, obese individuals have greater albuminuria, absolute GFR, and excretory burden. This has implications for chronic kidney disease management, screening, and research.

Influence of dietary protein on glomerular filtration before and after bariatric surgery: a cohort study

BACKGROUND

Obesity-associated elevations in glomerular filtration rate (GFR) are common and may play a role in the development of kidney disease, so identifying the underlying mechanism is important. We therefore studied whether reductions in dietary protein intake, which is known to modulate GFR, explain why GFR decreases after bariatric surgery-induced weight loss.

STUDY DESIGN

Cohort study with participants as their own controls.

SETTING & PARTICIPANTS

8 severely obese patients with normal kidney function were recruited from bariatric surgery centers in Indianapolis, IN. All participants were placed on a fixed-protein (50-g/d) diet for 1 week before and after a minimum of a 20-kg weight loss by bariatric surgery and were followed up closely by dieticians for adherence.

PREDICTOR

Ad lib versus low-protein diet before versus after bariatric surgery.

OUTCOME

Measured GFR, using repeated-measures analysis, was used to estimate the independent effects of diet and surgery.

MEASUREMENT

GFR was measured using plasma iohexol clearance.

RESULTS

A median of 32.9 (range, 19.5-54.4)kg was lost between the first presurgery visit and first postsurgery visit. Dietetic evaluations and urinary urea excretion confirmed that patients generally adhered to the study diet. GFRs on an ad lib diet were significantly higher before compared to after surgery (GFR medians were 144 (range, 114-178) and 107 (range, 85-147) mL/min, respectively; P=0.01). Although bariatric surgery (-26mL/min; P=0.005) and dietary sodium intake (+7.5mL/min per 100mg of dietary sodium; P=0.001) both influenced GFR, consuming a low-protein diet did not (P=0.7).

LIMITATIONS

Small sample size; mostly white women; possible lack of generalizability.

CONCLUSIONS

The decrease in GFR observed after bariatric surgery is explained at least in part by the effects of surgery and/or dietary sodium intake, but not by low dietary protein consumption.

Development of a definition for Rapid Progression (RP) of renal function in HIV-positive persons: the D:A:D study

Background

No consensus exists on how to define abnormally rapid deterioration in renal function (Rapid Progression, RP). We developed an operational definition of RP in HIV-positive persons with baseline estimated glomerular filtration rate (eGFR) >90 ml/min/1.73 m² (using Cockcroft Gault) in the Data Collection on Adverse Events of Anti-HIV Drugs (D:A:D) study from 2004 to 2011.

Methods

Two definitions were evaluated; RP definition A: An average eGFR decline (slope) ≥5 ml/min/1.73 m²/year over four years of follow-up with ≥3 eGFR measurements/year, last eGFR <90 ml/min/1.73 m² and an absolute decline ≥5 ml/min/1.73 m²/year in two consecutive years. RP definition B: An absolute annual decline ≥5 ml/min/1.73 m²/year in each year and last eGFR <90 ml/min/1.73 m². Sensitivity analyses were performed considering two and three years’ follow-up. The percentage with and without RP who went on to subsequently develop incident chronic kidney disease (CKD; 2 consecutive eGFRs <60 ml/min/1.73 m² and 3 months apart) was calculated.

Results

22,603 individuals had baseline eGFR ≥90 ml/min/1.73 m². 108/3655 (3.0%) individuals with ≥4 years’ follow-up and ≥3 measurements/year experienced RP under definition A; similar proportions were observed when considering follow-up periods of three (n=195/6375; 3.1%) and two years (n=355/10756; 3.3%). In contrast under RP definition B, greater proportions experienced RP when considering two years (n=476/10756; 4.4%) instead of three (n=48/6375; 0.8%) or four (n=15/3655; 0.4%) years’ follow-up. For RP definition A, 13 (12%) individuals who experienced RP progressed to CKD, and only (21) 0.6% of those without RP progressed to CKD (sensitivity 38.2% and specificity 97.4%); whereas for RP definition B, fewer RP individuals progressed to CKD.

Conclusions

Our results suggest using three years’ follow-up and at least two eGFR measurements per year is most appropriate for a RP definition, as it allows inclusion of a reasonable number of individuals and is associated with the known risk factors. The definition does not necessarily identify all those that progress to incident CKD, however, it can be used alongside other renal measurements to early identify and assess those at risk of developing CKD. Future analyses will use this definition to identify other risk factors for RP, including the role of antiretrovirals.

Accuracy of GFR estimation in obese patients

BACKGROUND AND OBJECTIVES

Adequate estimation of renal function in obese patients is essential for the classification of patients in CKD category as well as the dose adjustment of drugs. However, the body size descriptor for GFR indexation is still debatable, and formulas are not validated in patients with extreme variations of weight.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This study included 209 stages 1-5 CKD obese patients referred to the Department of Renal Function Study at the University Hospital in Lyon between 2010 and 2013 because of suspected renal dysfunction. GFR was estimated with the Chronic Kidney Disease and Epidemiology equation (CKD-EPI) and measured with a gold standard method (inulin or iohexol) not indexed (mGFR) or indexed to body surface area determined by the Dubois and Dubois formula with either real (mGFRr) or ideal (mGFRi) body weight. Mean bias (eGFR-mGFR), precision, and accuracy of mGFR were compared with the results obtained for nonobese participants (body mass index between 18.5 and 24.9) who had a GFR measurement during the same period of time.

RESULTS

Mean mGFRr (51.6 ± 24.2 ml/min per 1.73 m(2)) was significantly lower than mGFR, mGFRi, and eGFRCKD-EPI. eGFRCKD-EPI had less bias with mGFR (0.29; -1.7 to 2.3) and mGFRi (-1.62; -3.1 to 0.45) compared with mGFRr (8.7; 7 to 10). This result was confirmed with better accuracy for the whole cohort (78% for mGFR, 84% for mGFRi, and 72% for mGFRr) and participants with CKD stages 3-5. Moreover, the Bland Altman plot showed better agreement between mGFR and eGFRCKD-EPI. The bias between eGFRCKD-EPI and mGFRr was greater in obese than nonobese participants (8.7 versus 0.58, P<0.001).

CONCLUSIONS

This study shows that, in obese CKD patients, the performance of eGFRCKD-EPI is good for GFR ≤ 60 ml/min per 1.73 m(2). Indexation of mGFR with body surface area using ideal body weight gives less bias than mGFR scaled with body surface area using real body weight.

Plasma exogenous creatinine excretion for the assessment of renal function in avian medicine--pharmacokinetic modeling in racing pigeons (Columba livia)

The diagnostic evaluation of the glomerular filtration rate by urinary clearance has significant practical limitations in birds because urine is excreted together with feces. Thus, pharmacokinetic modeling of an exogenous plasma creatinine clearance could be useful for assessing renal creatinine excretion in birds. For this study, creatinine (50 mg/kg) was administered to 2 groups of 15 pigeons (Columba livia) each; in one group by the intravenous (IV) route and in the second by the intramuscular (IM) route. The time series of the plasma creatinine concentrations were analyzed by pharmacokinetic models. Body mass-specific creatinine excretion was determined for IV and IM administration to be between 6.30 and 6.44 mL/min per kg, respectively. Body surface area-specific creatinine clearance, which is related to the metabolic rate, was calculated between 0.506 and 0.523 mL/min per dm2, respectively. The results showed that IV as well as IM administration can be used for assessing renal creatinine excretion in pigeons. For practical reasons, IM administration is recommended, with the use of the Bateman function to calculate creatinine elimination.

Indexing glomerular filtration rate to body surface area: clinical consequences

BACKGROUND

Kidney function is mostly expressed in terms of glomerular filtration rate (GFR). A common feature is the expression as ml/min per 1.73 m(2) , which represents the adjustment of the individual kidney function to a standard body surface area (BSA) to allow comparison between individuals. We investigated the impact of indexing GFR to BSA in cancer patients, as this BSA indexation might affect the reported individual kidney function.

METHODS

Cross-sectional study of 895 adults who had their kidney function measured with (51) chrome ethylene diamine tetraacetic acid. Mean values of BSA-indexed GFR vs. mean absolute GFR were analyzed with a t-test for paired data. Bland-Altman plot was used to analyze agreement between the indexed and absolute GFR values.

RESULTS AND CONCLUSION

BSA-GFR in patients with a BSA <1.60 m(2) overestimated GFR with a bias of 10.08 ml/min (11.46%) and underestimated GFR in those with a BSA >2 m(2) with a bias up to -20.76 ml/min (-23.59%). BSA is not a good normalization index (NI) in patients with extreme body sizes. Therefore, until a better NI is found, we recommend clinicians to use the absolute GFR to calculate individual drug chemotherapy dosage as well as express individual kidney function.

Predicting the glomerular filtration rate in bariatric surgery patients

BACKGROUND/AIMS

Identifying the best method to estimate the glomerular filtration rate (GFR) in bariatric surgery patients has important implications for the clinical care of obese patients and research into the impact of obesity and weight reduction on kidney health. We therefore performed such an analysis in patients before and after surgical weight loss.

METHODS

Fasting measured GFR (mGFR) by plasma iohexol clearance before and after bariatric surgery was obtained in 36 severely obese individuals. Estimated GFR was calculated using the Modification of Diet in Renal Disease equation, the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation using serum creatinine only, the CKD-EPI equation using serum cystatin C only and a recently derived equation that uses both serum creatinine and cystatin C (CKD-EPIcreat-cystC) and then compared to mGFR.

RESULTS

Participants were primarily middle-aged white females with a mean baseline body mass index of 46 ± 9, serum creatinine of 0.81 ± 0.24 mg/dl and mGFR of 117 ± 40 ml/min. mGFR had a stronger linear relationship with inverse cystatin C before (r = 0.28, p = 0.09) and after (r = 0.38, p = 0.02) surgery compared to the inverse of creatinine (before: r = 0.26, p = 0.13; after: r = 0.11, p = 0.51). mGFR fell by 17 ± 35 ml/min (p = 0.007) following surgery. The CKD-EPIcreat-cystC was unquestionably the best overall performing estimating equation before and after surgery, revealing very little bias and a capacity to estimate mGFR within 30% of its true value over 80% of the time. This was true whether or not mGFR was indexed for body surface area.

CONCLUSIONS

In severely obese bariatric surgery patients with normal kidney function, cystatin C is more strongly associated with mGFR than is serum creatinine. The CKD-EPIcreat-cystC equation best predicted mGFR both before and after surgery.

The use of absolute values improves performance of estimation formulae: a retrospective cross sectional study

BACKGROUND

Estimation of Glomerular Filtration Rate (GFR) by equations such as Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) or Modification of Diet in Renal Disease (MDRD) is usually expressed as a Body Surface Area (BSA) indexed value (ml/min per 1.73 m²). This can have severe clinical consequences in patients with extreme body sizes, resulting in an underestimation in the case of obesity or an overestimation of GFR in the case of underweight patients. The aim of this study was to compare the performance of both estimation formula expressed in ml/min, instead of ml/min per 1.73 m², with a reference method.

METHODS

Retrospective single centre cross sectional study of 185 patients. GFR was measured with 51Cr-EDTA and estimated with CKD-EPI and MDRD. Bias, precision and accuracy of absolute estimated GFR was calculated.

RESULTS

Bias of CKD-EPI and MDRD formulae expressed as an absolute value was 0.49 and 0.27 ml/min respectively, which is lower than previously reported. Precision was 12.95 and 16.33 and accuracy expressed as P30 was over 92.43% for CKD-EPI. There were no significant differences in GFR between the reference method and the estimation formulae.

CONCLUSIONS

The performance of CKD-EPI and MDRD formulae can be significantly improved in the individual patient if the absolute values are used by removing the BSA normalization factor. Absolute estimated GFR by CKD-EPI is comparable to measured GFR, improving the performance of this formula in the assessment of individual kidney function, thus providing clinicians with an alternative to reference methods.

Subclinical cardiovascular disease is associated with a high glomerular filtration rate in the nondiabetic general population

A reduced glomerular filtration rate (GFR) in chronic kidney disease is a risk factor for cardiovascular disease. However, evidence indicates that a high GFR may also be a cardiovascular risk factor. This issue remains unresolved due to a lack of longitudinal studies of manifest cardiovascular disease with precise GFR measurements. Here, we performed a cross-sectional study of the relationship between high GFR measured as iohexol clearance and subclinical cardiovascular disease in the Renal Iohexol Clearance Survey in Tromsø 6 (RENIS-T6), a representative sample of the middle-aged general population. A total of 1521 persons without cardiovascular disease, chronic kidney disease, diabetes, or micro- or macroalbuminuria were examined with carotid ultrasonography and electrocardiography. The GFR in the highest quartile was associated with an increased odds ratio of having total carotid plaque area greater than the median of non-zero values (odds ratio 1.56, 95% confidence interval 1.02-2.39) or electrocardiographic signs of left ventricular hypertrophy (odds ratio 1.62, 95% confidence interval 1.10-2.38) compared to the lowest quartile. The analyses were adjusted for cardiovascular risk factors, urinary albumin excretion, and fasting serum glucose. Thus, high GFR is associated with carotid atherosclerosis and left ventricular hypertrophy and should be investigated as a possible risk factor for manifest cardiovascular disease in longitudinal studies.

A comparison of estimated glomerular filtration rates using Cockcroft-Gault and the Chronic Kidney Disease Epidemiology Collaboration estimating equations in HIV infection

OBJECTIVES

The aim of this study was to determine whether the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI)- or Cockcroft-Gault (CG)-based estimated glomerular filtration rates (eGFRs) performs better in the cohort setting for predicting moderate/advanced chronic kidney disease (CKD) or end-stage renal disease (ESRD).

METHODS

A total of 9521 persons in the EuroSIDA study contributed 133 873 eGFRs. Poisson regression was used to model the incidence of moderate and advanced CKD (confirmed eGFR < 60 and < 30 mL/min/1.73 m(2) , respectively) or ESRD (fatal/nonfatal) using CG and CKD-EPI eGFRs.

RESULTS

Of 133 873 eGFR values, the ratio of CG to CKD-EPI was ≥ 1.1 in 22 092 (16.5%) and the difference between them (CG minus CKD-EPI) was ≥ 10 mL/min/1.73 m(2) in 20 867 (15.6%). Differences between CKD-EPI and CG were much greater when CG was not standardized for body surface area (BSA). A total of 403 persons developed moderate CKD using CG [incidence 8.9/1000 person-years of follow-up (PYFU); 95% confidence interval (CI) 8.0-9.8] and 364 using CKD-EPI (incidence 7.3/1000 PYFU; 95% CI 6.5-8.0). CG-derived eGFRs were equal to CKD-EPI-derived eGFRs at predicting ESRD (n = 36) and death (n = 565), as measured by the Akaike information criterion. CG-based moderate and advanced CKDs were associated with ESRD [adjusted incidence rate ratio (aIRR) 7.17; 95% CI 2.65-19.36 and aIRR 23.46; 95% CI 8.54-64.48, respectively], as were CKD-EPI-based moderate and advanced CKDs (aIRR 12.41; 95% CI 4.74-32.51 and aIRR 12.44; 95% CI 4.83-32.03, respectively).

CONCLUSIONS

Differences between eGFRs using CG adjusted for BSA or CKD-EPI were modest. In the absence of a gold standard, the two formulae predicted clinical outcomes with equal precision and can be used to estimate GFR in HIV-positive persons.

Higher extracellular fluid volume in women is concealed by scaling to body surface area

OBJECTIVE

The objective was to assess body surface area (BSA) for scaling extracellular fluid volume (ECV) in comparison with estimated lean body mass (LBM) and total body water (TBW) across a range of body mass indices (BMI).

METHODS

This was a multi-centre study from 15 centres that submitted raw data from routine measurement of GFR in potential kidney transplant donors. There were 819 men and 1059 women in total. ECV was calculated from slope-intercept and slope-only measurements of GFR. ECV was scaled using two methods: Firstly, division of ECV by the scaling variable (ratio method), and secondly the regression method of Turner and Reilly. Subjects were placed into five BMI groups: < 20, 20-24.9, 25-29.9, 30-34.9, and 35 + kg/m(2). LBM and TBW were estimated from previously published, gender-specific prediction equations.

RESULTS

Ratio and regression scaling gave almost identical results. ECV scaled to BSA by either method was higher in men in all BMI groups but ECV scaled to LBM and TBW was higher in women. There was, however, little difference between men and women in respect to ECV per unit weight in any BMI group, even though women have 10% more adipose tissue. The relations between TBW and BSA and between LBM and BSA, but not between LBM and TBW, were different between men and women.

CONCLUSION

Lean tissue in women contains more extracellular water than in men, a difference that is obscured by scaling to BSA. The likely problem with BSA is its insensitivity to body composition.

Central body fat distribution associates with unfavorable renal hemodynamics independent of body mass index

Central distribution of body fat is associated with a higher risk of renal disease, but whether it is the distribution pattern or the overall excess weight that underlies this association is not well understood. Here, we studied the association between waist-to-hip ratio (WHR), which reflects central adiposity, and renal hemodynamics in 315 healthy persons with a mean body mass index (BMI) of 24.9 kg/m(2) and a mean (125)I-iothalamate GFR of 109 ml/min per 1.73 m(2). In multivariate analyses, WHR was associated with lower GFR, lower effective renal plasma flow, and higher filtration fraction, even after adjustment for sex, age, mean arterial pressure, and BMI. Multivariate models produced similar results regardless of whether the hemodynamic measures were indexed to body surface area. Thus, these results suggest that central body fat distribution, independent of BMI, is associated with an unfavorable pattern of renal hemodynamic measures that could underlie the increased renal risk reported in observational studies.

Using mathematical algorithms to modify glomerular filtration rate estimation equations

BACKGROUND

The equations provide a rapid and low-cost method of evaluating glomerular filtration rate (GFR). Previous studies indicated that the Modification of Diet in Renal Disease (MDRD), Chronic Kidney Disease-Epidemiology (CKD-EPI) and MacIsaac equations need further modification for application in Chinese population. Thus, this study was designed to modify the three equations, and compare the diagnostic accuracy of the equations modified before and after.

METHODOLOGY

With the use of (99 m)Tc-DTPA renal dynamic imaging as the reference GFR (rGFR), the MDRD, CKD-EPI and MacIsaac equations were modified by two mathematical algorithms: the hill-climbing and the simulated-annealing algorithms.

RESULTS

A total of 703 Chinese subjects were recruited, with the average rGFR 77.14±25.93 ml/min. The entire modification process was based on a random sample of 80% of subjects in each GFR level as a training sample set, the rest of 20% of subjects as a validation sample set. After modification, the three equations performed significant improvement in slop, intercept, correlated coefficient, root mean square error (RMSE), total deviation index (TDI), and the proportion of estimated GFR (eGFR) within 10% and 30% deviation of rGFR (P10 and P30). Of the three modified equations, the modified CKD-EPI equation showed the best accuracy.

CONCLUSIONS

Mathematical algorithms could be a considerable tool to modify the GFR equations. Accuracy of all the three modified equations was significantly improved in which the modified CKD-EPI equation could be the optimal one.

The GFR and GFR decline cannot be accurately estimated in type 2 diabetics

There are no adequate studies that have formally tested the performance of different estimating formulas in patients with type 2 diabetes both with and without overt nephropathy. Here we evaluated the agreement between baseline GFRs, GFR changes at month 6, and long-term GFR decline measured by iohexol plasma clearance or estimated by 15 creatinine-based formulas in 600 type 2 diabetics followed for a median of 4.0 years. Ninety patients were hyperfiltering. The number of those identified by estimation formulas ranged from 0 to 24:58 were not identified by any formula. Baseline GFR was significantly underestimated and a 6-month GFR reduction was missed in hyperfiltering patients. Long-term GFR decline was also underestimated by all formulas in the whole study group and in hyper-, normo-, and hypofiltering patients considered separately. Five formulas generated positive slopes in hyperfiltering patients. Baseline concordance correlation coefficients and total deviation indexes ranged from 32.1% to 92.6% and from 0.21 to 0.53, respectively. Concordance correlation coefficients between estimated and measured long-term GFR decline ranged from -0.21 to 0.35. The agreement between estimated and measured values was also poor within each subgroup considered separately. Thus, our study questions the use of any estimation formula to identify hyperfiltering patients and monitor renal disease progression and response to treatment in type 2 diabetics without overt nephropathy.

Comparison of serum cystatin C, serum creatinine, measured GFR, and estimated GFR to assess the risk of kidney failure in American Indians with diabetic nephropathy

BACKGROUND

We compared values of baseline serum cystatin C (SCysC), serum creatinine (SCr), and measured glomerular filtration rate (mGFR) for predicting end-stage renal disease (ESRD) in patients with type 2 diabetes and elevated albuminuria.

STUDY DESIGN

Observational longitudinal study.

SETTING & PARTICIPANTS

Pima Indians with type 2 diabetes and elevated albumin-creatinine ratio (ACR ≥30 mg/g).

PREDICTORS

Baseline SCysC, SCr, and mGFR.

OUTCOMES & MEASUREMENTS

Individuals were followed up from their first examination with diabetes and ACR ≥30 mg/g until December 2010, onset of ESRD, or death, whichever came first. Incidence rates adjusted for age and sex were computed by Mantel-Haenszel stratification. The abilities of SCysC, SCr, and mGFR values to predict ESRD were compared with receiver operating characteristic curves.

RESULTS

Of 234 Pima Indians with a mean age of 42.8 years who were followed up for a median of 10.7 (range, 0.6-21.3) years, 68 (29%) developed ESRD. The incidence of ESRD was significantly higher in patients in the lowest versus highest tertile of 1/SCysC (incidence rate ratio, 2.43; 95% CI, 1.31-4.50). By contrast, mGFR and 1/SCr had J-shaped associations with ESRD. In unadjusted analyses, 1/SCysC had the highest area under the receiver operating characteristic curve (AUROC; 0.719 ± 0.035) and mGFR had the lowest (0.585 ± 0.042; P < 0.001); the AUROC for 1/SCr was intermediate (0.672 ± 0.040; P = 0.1 and P = 0.03 vs 1/SCysC and mGFR, respectively). In analyses adjusted for age, sex, diabetes duration, height, weight, hemoglobin A1c level, and ACR, 1/SCysC had the highest AUROC (0.845 ± 0.026). Models with mGFR or 1/SCr alone had similar AUROCs (P = 0.9) and both were lower than the model with 1/SCysC alone (P = 0.02 and P = 0.03, respectively).

LIMITATIONS

The predictive values of the filtration markers are limited to the extent that their precision is based on a single measurement.

CONCLUSIONS

SCysC level was a better predictor of ESRD than mGFR or SCr level in Pima Indians with type 2 diabetes and elevated albuminuria.

The effect of very low-calorie diets on renal and hepatic outcomes: a systematic review

Very low-calorie diets (VLCDs) are an effective means by which to induce clinically significant weight loss. However, their acceptance by health care practitioners and the public is generally lower than that for other nonsurgical weight loss methods. Whilst there is currently little evidence to suggest they have any detrimental effect on hepatic and renal health, data assessing these factors remain limited. We carried out a systematic review of the literature on randomized controlled trials that had a VLCD component and that reported outcomes for hepatic and renal health, published between January 1980 and December 2012. Cochrane criteria were followed, and eight out of 196 potential articles met the inclusion criteria. A total of 548 participants were recruited across the eight studies. All eight studies reported significant weight loss following the VLCD. Changes in hepatic and renal outcomes were variable but generally led to either no change or improvements in either of these. Due to the heterogeneity in the quality and methodology of the studies included, the effect of VLCDs on hepatic and renal outcomes remains unclear at this stage. Further standardized research is therefore required to fully assess the impact of VLCDs on these outcome measures, to better guide clinical practice.

Compliance with a structured weight loss program is associated with reduced systolic blood pressure in obese patients with chronic kidney disease

BACKGROUND

The effectiveness of lifestyle-based weight loss programs in obese patients with chronic disease has not been widely studied. This study examined the effectiveness of a weight management program (WMP), and sought to determine factors associated with successful weight loss in obese patients with chronic kidney disease (CKD).

METHODS

In this prospective cohort study, all patients with a body mass index (BMI) of >30 kg/m(2) referred to our clinic from January 2005 to December 2008 and who commenced a structured WMP of an energy-reduced renal diet, exercise, and pharmacotherapy were included in the analyses. Changes in body weight and associated variables up to 24 months were assessed with intention-to-treat mixed linear models and predictors of weight loss were identified with multiple linear regression.

RESULTS

One hundred and thirty-five patients (56% male), of mean age 52.2 years and BMI 36.4 kg/m(2) commenced the WMP. Significant weight loss was achieved for all patients at 6, 12, 18, and 24 months. Weight loss at 12 months was predicted by compliance and age, but not by baseline BMI, blood pressure (BP), stage of CKD or pharmacotherapy use. Greater compliance was associated with decreased systolic BP, with no change in mean antihypertensive medication dose.

CONCLUSIONS

Significant weight loss was achieved, demonstrating the effectiveness of the WMP, and compliance with a structured program improved weight loss and systolic BP.

Podocyte detachment and reduced glomerular capillary endothelial fenestration promote kidney disease in type 2 diabetic nephropathy

Podocyte detachment and reduced endothelial cell fenestration and relationships between these features and the classic structural changes of diabetic nephropathy have not been described in patients with type 2 diabetes. Here we studied these relationships in 37 Pima Indians with type 2 diabetes of whom 11 had normal albuminuria, 16 had microalbuminuria, and 10 had macroalbuminuria. Biopsies from 10 kidney donors (not American Indians) showed almost undetectable (0.03%) podocyte detachment and 43.5% endothelial cell fenestration. In patients with type 2 diabetes, by comparison, the mean percentage of podocyte detachment was significantly higher in macroalbuminuria (1.48%) than in normal albuminuria (0.41%) or microalbuminuria (0.37%). Podocyte detachment correlated significantly with podocyte number per glomerulus and albuminuria. The mean percentage of endothelial cell fenestration was significantly lower in macroalbuminuria (19.3%) than in normal albuminuria (27.4%) or microalbuminuria (27.2%) and correlated significantly with glomerular basement membrane thickness, albuminuria, fractional mesangial area, and the glomerular filtration rate (iothalamate clearance). Podocyte detachment and diminished endothelial cell fenestration were not correlated, but were related to classic lesions of diabetic nephropathy. Thus, our findings confirm the important role these injuries play in the development and progression of kidney disease in type 2 diabetes, just as they do in type 1 diabetes. Whether podocyte detachment creates conduits for proteins to escape the glomerular circulation and reduced endothelial fenestration lowers glomerular hydraulic permeability requires further study.

Anorexia nervosa and the kidney

Anorexia nervosa is a common psychiatric disorder that disproportionately affects adolescents and young adults and is associated with high rates of morbidity and mortality. Anorexia nervosa can affect the kidney in numerous ways, including increased rates of acute kidney injury and chronic kidney disease, electrolyte abnormalities, and nephrolithiasis. Additionally, the diagnosis and treatment of anorexia nervosa-associated kidney diseases are challenging, reflecting complications such as refeeding syndrome, as well as the limitations of serum creatinine level in this population to estimate kidney function and the psychosocial challenges inherent with treating systemic manifestations of psychiatric conditions. In this review, we discuss kidney diseases and kidney-associated conditions that occur in individuals with anorexia nervosa, summarizing many of the challenges in treating patients with this disease.

The impact of renal function on outcomes of bariatric surgery

The effect of CKD on the risks of bariatric surgery is not well understood. Using the American College of Surgeons National Surgical Quality Improvement Program Participant Use File, we analyzed 27,736 patients who underwent bariatric surgery from 2006 through 2008. Before surgery, 34 (0.12%) patients were undergoing long-term dialysis. Among those not undergoing dialysis, 20,806 patients (75.0%) had a normal estimated GFR or stage 1 CKD, 5011 (18.07%) had stage 2 CKD, 1734 (6.25%) had stage 3 CKD, 94 (0.34%) had stage 4 CKD, and 91 (0.33%) had stage 5 CKD. In an unadjusted analysis, CKD stage was directly associated with complication rate, ranging from 4.6% for those with stage 1 CKD or normal estimated GFR to 9.9% for those with stage 5 CKD (test for trend, P<0.001). Multivariable logistic regression demonstrated that CKD stage predicts higher complication rates (odds ratio for each higher CKD stage, 1.30) after adjustment for diabetes and hypertension. Although patients with higher CKD stage had higher complication rates, the absolute incidence of complications remained <10%. In conclusion, these data demonstrate higher risks of bariatric surgery among patients with worse renal function, but whether the potential benefits outweigh the risks in this population requires further study.

Indexing of renal function parameters by body surface area: intelligence or folly?

Indexation of glomerular filtration rate (GFR) by body surface area (BSA) is often done without raising any questions. In this article, we will shortly review the limitations of such indexation and illustrate potential errors in clinical practice due to this indexation. Adjusting the GFR by BSA is particularly misleading in patients with abnormal body size (obese and anorectic). We will also insist on the fact that indexation by BSA is not required for the GFR longitudinal follow-up. Additionally, we will discuss the implications and consequences of BSA indexation on the creatinine-based equations, such as the Cockcroft-Gault and the MDRD study equations.

Extracellular fluid volume and glomerular filtration rate in 1878 healthy potential renal transplant donors: effects of age, gender, obesity and scaling

Aim. The aim of this study was to investigate the influence of age, gender, obesity and scaling on glomerular filtration rate (GFR) and extracellular fluid volume (ECV) in healthy subjects.

METHODS

This is a retrospective multi-centre study of 1878 healthy prospective kidney transplant donors (819 men) from 15 centres. Age and body mass index (BMI) were not significantly different between men and women. Slope-intercept GFR was measured (using Cr-51-EDTA in 14 centres; Tc-99m-DTPA in one) and scaled to body surface area (BSA) and lean body mass (LBM), both estimated from height and weight. GFR was also expressed as the slope rate constant, with one-compartment correction (GFR/ECV). ECV was measured as the ratio, GFR to GFR/ECV.

RESULTS

ECV was age independent but GFR declined with age, at a significantly faster rate in women than men. GFR/BSA was higher in men but GFR/ECV and GFR/LBM were higher in women. Young women (<30 years) had higher GFR than young men but the reverse was recorded in the elderly (>65 years). There was no difference in GFR between obese (BMI>30 kg/m2) and non-obese men. Obese women, however, had lower GFR than non-obese women and negative correlations were observed between GFR and both BMI and %fat. The decline in GFR with age was no faster in obese versus non-obese subjects. ECV/BSA was higher in men but ECV/LBM was higher in women. ECV/weight was almost gender independent, suggesting that fat-free mass in women contains more extracellular water. BSA is therefore a misleading scaling variable.

CONCLUSION

There are several significant differences in GFR and ECV between healthy men and women.

Early renal function decline in type 2 diabetes

BACKGROUND AND OBJECTIVES

Early decline in GFR may reflect progressive kidney disease in type 1 diabetes, but its predictive value in type 2 diabetes is uncertain.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

In this longitudinal study, GFR was measured serially over approximately 4.0 years in 195 Pima Indians with type 2 diabetes. Renal function decline (RFD) was defined during this initial period by an average GFR loss ≥3.3%/yr, as defined previously in type 1 diabetes. Subsequently, participants were followed for up to 17.8 years to ESRD onset, death, or December 31, 2010, whichever came first.

RESULTS

RFD prevalence during the initial period was 32% in 68 participants with normal baseline albuminuria (albumin/creatinine ratio [ACR] < 30 mg/g), 42% in 88 with microalbuminuria (ACR 30 to <300 mg/g), and 74% in 39 with macroalbuminuria (ACR ≥300 mg/g; P<0.001). The cumulative incidence of ESRD 10 years after the initial period was 41% in those with RFD and 15% in those without (P<0.001); 41 of the 49 ESRD cases (83.7%) occurred in participants who had or developed macroalbuminuria during the initial period. When adjusted for age, sex, diabetes duration, and hemoglobin A1c, the ESRD hazard rate was 4.78 times (95% confidence interval, 2.39-9.58) as high in those with RFD as in those without; further adjustment for albuminuria attenuated this association (hazard ratio, 1.79; 95% confidence interval, 0.82-3.91).

CONCLUSIONS

In type 2 diabetes, loss of GFR often occurs before the onset of macroalbuminuria, but a decline predictive of ESRD is strongly dependent on progression to macroalbuminuria.

Cigarette smoking and the association with glomerular hyperfiltration and proteinuria in healthy middle-aged men

BACKGROUND AND OBJECTIVES

Glomerular hyperfiltration and albuminuria accompanied by early-stage diabetic kidney disease predict future renal failure. Cigarette smoking has reported to be associated with elevated GFR in cross-sectional studies and with renal deterioration in longitudinal studies. The degree of glomerular hyperfiltration and proteinuria associated with smoking, which presumably is a phenomenon of early renal damage, has not been investigated in a satisfying manner so far.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This study included 10,118 Japanese men aged 40 to 55 years without proteinuria or renal dysfunction at entry. Estimated GFR was calculated using the Modification of Diet in Renal Disease equation for Japanese. Glomerular hyperfiltration was defined as estimated GFR ≥117.0 ml/min per 1.73 m(2), which was the upper 2.5th percentile value of estimated GFR in the total population. Proteinuria was detected using standard dipstick.

RESULTS

During the 6-year observation period, there were 449 incident cases of glomerular hyperfiltration and 1653 cases of proteinuria. Current smokers had a 1.32-time higher risk for the development of glomerular hyperfiltration and a 1.51-time higher risk for proteinuria than nonsmokers after adjustment for baseline age, body mass index, systolic and diastolic BP, antihypertensive medication, diabetes, alcohol consumption, regular leisure-time physical activity, and estimated GFR. Both daily and cumulative cigarette consumption were associated with an increased risk for glomerular hyperfiltration and proteinuria in a dose-response manner.

CONCLUSIONS

In middle-aged Japanese men, smoking was associated with an increased risk of glomerular hyperfiltration and dipstick proteinuria. Of importance, past smokers did not exhibit any increased risk for these conditions.

Predictive performance of 12 equations for estimating glomerular filtration rate in severely obese patients

ABSTRACT Objective: Considering that the Cockcroft-Gault formula and the equation of diet modification in renal disease are amply used in clinical practice to estimate the glomerular filtration rate, although they seem to have low accuracy in obese patients, the present study intends to evaluate the predictive performance of 12 equations used to estimate the glomerular filtration rate in obese patients. Methods: This is a cross-sectional retrospective study, conducted between 2007 and 2008 and carried out at a university, of 140 patients with severe obesity (mean body mass index 44 ± 4.4 kg/m2). The glomerular filtration rate was determined by means of 24-hour urine samples. Patients were classified into one or more of the four subgroups: impaired glucose tolerance (n = 43), diabetic (n = 24), metabolic syndrome (n = 76), and/or hypertension (n = 66). We used bias, precision, and accuracy to assess the predictive performance of each equation in the entire group and in the subgroups. Results: In renal disease, Cockcroft-Gault's formula and the diet modification equation are not precise in severely obese patients (precision: 40.9 and 33.4, respectively). Sobh's equation showed no bias in the general group or in two subgroups. Salazar-Corcoran's and Sobh's equations showed no bias for the entire group (Bias: −5.2, 95% confidence interval (CI) = −11.4, 1.0, and 6. 2; 95%CI = −0.3, 12.7, respectively). All the other equations were imprecise for the entire group. Conclusion: Of the equations studied, those of Sobh and Salazar-Corcoran seem to be the best for estimating the glomerular filtration rate in severely obese patients analyzed in our study.

GFR normalized to total body water allows comparisons across genders and body sizes

The normalization of GFR to a standardized body-surface area of 1.73 m(2) impedes comparison of GFR across individuals of different genders, heights, or weights. Ideally, GFR should be normalized to a parameter that best explains variation in GFR. Here, we measured true GFR by iohexol clearance in a representative sample of 1627 individuals from the general population who did not have diabetes, cardiovascular disease, or kidney disease. We also estimated total body water (TBW), extracellular fluid volume, lean body mass, liver volume, metabolic rate, and body-surface area. We compared two methods of normalizing GFR to these physiologic variables: (1) the conventional method of scaling GFR to each physiologic variable by simple division and (2) a method based on regression of the GFR on each variable. TBW explained a higher proportion of the variation in GFR than the other physiologic variables. GFR adjusted for TBW by the regression method exhibited less dependence on gender, height, and weight compared with the other physiologic variables. Thus, adjusting GFR for TBW by the regression method allows direct comparisons between individuals of different genders, weights, and heights. We propose that regression-based normalization of GFR to a standardized TBW of 40 L should replace the current practice of normalizing GFR to 1.73 m(2) of body-surface area.

The four-variable modification of diet in renal disease formula underestimates glomerular filtration rate in obese type 2 diabetic individuals with chronic kidney disease

AIMS/HYPOTHESIS

GFR is commonly estimated using the four-variable Modification of Diet in Renal Disease (MDRD) formula and this forms the basis for classification of chronic kidney disease (CKD). We investigated the effect of obesity on the estimation of glomerular filtration rate in type 2 diabetic participants with CKD.

METHODS

We enrolled 111 patients with type 2 diabetes mellitus in different stages of CKD. GFR was measured using (51)Cr-labelled EDTA plasma clearance and was estimated using the four-variable MDRD formula.

RESULTS

The bias between estimated and measured GFR was -22.4 (-33.8 to -11.0) p < 0.001 in the obese group compared with -6.04 (-17.6 to -5.5) p = 0.299 in the non-obese group. When GFR was indexed to body surface area of 1.73 m(2), the bias remained significant at -9.4 (-13.4 to -5.4) p < 0.001 in the obese participants.

CONCLUSIONS/INTERPRETATION

This study suggests that the four-variable MDRD formula significantly underestimates GFR in obese type 2 diabetic participants with CKD.