Errors induced by indexing glomerular filtration rate for body surface area: reductio ad absurdum

Central Body Fat Distribution and Kidney Function after Living Kidney Donation

BACKGROUND

In most screening guidelines, high body mass index (BMI) is considered a contraindication for kidney donation. New insights suggest that central body fat distribution might provide greater power in assessing kidney risk. This study aimed to determine whether BMI and central body fat distribution measures are associated with long-term kidney function after donor nephrectomy. We hypothesized that higher BMI, waist circumference (WC), and waist-to-height ratio (WHtR) were associated with lower kidney function long term after donation.

METHODS

The study population consisted of living kidney donors. BMI, WC, and WHtR were measured during donor screening. The outcome postdonation kidney function was assessed using measured GFR (mGFR) (mGFR, 125 I-iothalamate infusion) at 3 months ( n =1042), 5 years ( n =556), and 10 years ( n =210) of follow-up. Primary multivariable linear regression analyses were performed with BMI and WC and secondary analyses with WHtR. Linear mixed models were performed to investigate change in postdonation eGFR.

RESULTS

The donor age was 52±11 years, and 48% were male. The mean BMI was 26.1±3.6 kg/m 2 , and WC was 91±11 cm. Higher predonation BMI was associated with lower mGFR throughout follow-up: -1.35 (95% confidence interval [CI], -1.95 to -0.80), -1.55 (95% CI, -2.50 to -0.65), and -2.35 (95% CI, -4.10 to -0.60) ml/min per m 2 per 5 kg/m 2 higher BMI at 3 months, 5, and 10 years after donation, respectively, adjusted for sex, age, and predonation GFR. For WC, differences in mGFR were -1.30 (95% CI, -1.70 to -0.90), -1.50 (95% CI, -2.20 to -0.80), and -1.70 (95% CI, -3.00 to -0.50) ml/min per m 2 per 10 cm higher WC at 3 months, 5, and 10 years after donation, respectively. In male donors, BMI and WC were significantly associated with a negative postdonation change in eGFR.

CONCLUSIONS

Higher BMI and WC were independently associated with lower GFR (long term) after living kidney donation.

The error of estimated GFR in predialysis care

The error of estimated glomerular filtration rate (eGFR) and its consequences in predialysis are unknown. In this prospective multicentre study, 315 predialysis patients underwent measured GFR (mGFR) by the clearance of iohexol and eGFR by 52 formulas. Agreement between eGFR and mGFR was evaluated by concordance correlation coefficient (CCC), total deviation index (TDI) and coverage probability (CP). In a sub-analysis we assessed the impact of eGFR error on decision-making as (i) initiating dialysis, (ii) preparation for renal replacement therapy (RRT) and (iii) continuing clinical follow-up. For this sub-analysis, patients who started RRT due to clinical indications (uremia, fluid overload, etc.) were excluded. eGFR had scarce precision and accuracy in reflecting mGFR (average CCC 0.6, TDI 70% and cp 22%) both in creatinine- and cystatin-based formulas. Variations -larger than 10 ml/min- between mGFR and eGFR were frequent. The error of formulas would have suggested (a) premature preparation for RTT in 14% of stable patients evaluated by mGFR; (b) to continue clinical follow-up in 59% of subjects with indication for RTT preparation due to low GFRm and (c) to delay dialysis in all asymptomatic patients (n = 6) in whom RRT was indicated based on very low mGFR. The error of formulas in predialysis was frequent and large and may have consequences in clinical care.

Absolute and relative GFR and contrast medium dose/GFR ratio: cornerstones when predicting the risk of acute kidney injury

Glomerular filtration rate (GFR) is considered the best overall index of kidney function in health and disease and its use is recommended to evaluate the risk of iodine contrast medium-induced acute kidney injury (CI-AKI) either as a single parameter or as a ratio between the total contrast medium dose (gram iodine) and GFR. GFR may be expressed in absolute terms (mL/min) or adjusted/indexed to body surface area, relative GFR (mL/min/1.73 m2). Absolute and relative GFR have been used interchangeably to evaluate the risk of CI-AKI, which may be confusing and a potential source of errors. Relative GFR should be used to assess the GFR category of renal function as a sign of the degree of kidney damage and sensitivity for CI-AKI. Absolute GFR represents the excretion capacity of the individual and may be used to calculate the gram-iodine/absolute GFR ratio, an index of systemic drug exposure (amount of contrast medium in the body) that relates to toxicity. It has been found to be an independent predictor of AKI following percutaneous coronary angiography and interventions but has not yet been fully validated for computed tomography (CT). Prospective studies are warranted to evaluate the optimal gram-iodine/absolute GFR ratio to predict AKI at various stages of renal function at CT. Only GFR estimation (eGFR) equations based on standardized creatinine and/or cystatin C assays should be used. eGFRcystatin C/eGFRcreatinine ratio < 0.6 indicating selective glomerular hypofiltration syndrome may have a stronger predictive power for postcontrast AKI than creatinine-based eGFR. CLINICAL RELEVANCE STATEMENT: Once the degree of kidney damage is established by estimating relative GFR (mL/min/1.73 m2), contrast dose in relation to renal excretion capacity [gram-iodine/absolute GFR (mL/min)] may be the best index to evaluate the risk of contrast-induced kidney injury. KEY POINTS: • Relative glomerular filtration rate (GFR; mL/min/1.73 m2) should be used to assess the GFR category as a sign of the degree of kidney damage and sensitivity to contrast medium-induced acute kidney injury (CI-AKI). • Absolute GFR (mL/min) is the individual's actual excretion capacity and the contrast-dose/absolute GFR ratio is a measure of systemic exposure (amount of contrast medium in the body), relates to toxicity and should be expressed in gram-iodine/absolute GFR (mL/min). • Prospective studies are warranted to evaluate the optimal contrast medium dose/GFR ratio predicting the risk of CI-AKI at CT and intra-arterial examinations.

The Impact of Early-Stage Chronic Kidney Disease on Weight Loss Outcomes After Gastric Bypass

PURPOSE

Weight loss achieved through bariatric metabolic surgery was demonstrated to be effective at reversing chronic kidney dysfunction associated with obesity-related glomerulopathy. However, robust data on how pre-operative kidney status impacts on bariatric metabolic surgery weight loss outcomes is still lacking. The aim of this study was to evaluate the impact of kidney dysfunction on weight loss outcomes after bariatric metabolic surgery.

METHODS

Patients with obesity to be submitted to gastric bypass surgery underwent a pre-operative evaluation of creatinine clearance, estimated glomerular filtration rate (eGFR), proteinuria, and albuminuria in 24-hour urine. Body mass index (BMI), % total weight loss (%TWL), and % excess BMI loss (%EBMIL) were assessed at 6 and 12 months after surgery.

RESULTS

Before surgery, patients (N=127) had a mean BMI of 39.6 ± 3.0 kg/m2, and 56.7% (n=72) had a creatinine clearance > 130 mL/min, 23.6% (n= 30) presented proteinuria > 150 mg/24h, and 15.0% (n= 19) presented albuminuria > 30 mg/24h. After surgery, the mean BMI was 27.7 kg/m2 and 25.0 kg/m2 at 6 and 12 months, respectively (p<0.0001). The %TWL was lower in patients with pre-operative eGFR < percentile 25 (34.4 ± 5.8% vs 39.4 ± 4.9%, p=0.0007, at 12 months). There were no significant correlations between weight loss metrics and pre-operative creatinine clearance rate, proteinuria, or albuminuria.

CONCLUSION

Early-stage chronic kidney disease (G2) has a negative impact on short-term weight loss outcomes after bariatric metabolic surgery, albeit in a magnitude inferior to the clinically relevant threshold.

The Effect of Elective Ligation of the Arteriovenous Fistula on Cardiac and Renal Functions in Kidney Transplant Recipients

Key Points

Surgical AVF ligation in KTRs is associated with a significant increase in diastolic BP while systolic BP remains stable. AVF closure in KTRs leads to an improvement of LV and LA morphology and a decrease in serum NT-proBNP levels. There is no significant effect of AVF ligation on kidney allograft function: The eGFR remains stable over time.

Background

Kidney transplantation is considered as the best kidney replacement therapy, and arteriovenous fistula (AVF) is the preferred vascular access for hemodialysis. The systematic ligation of a functioning AVF in stable kidney transplant recipients (KTRs) remains debatable.

Methods

In this prospective study, we investigated the hemodynamic effect of the surgical closure of AVF in KTRs. Forty-three KTRs underwent an ambulatory BP monitoring before surgical closure of AVF (T0) and 12 months later (M12), as well as measurement of serum cardiac biomarkers (i.e. , soluble suppression of tumorigenicity 2, N-terminal pro b-type natriuretic peptide [NT-proBNP], and galectin-3). Serum tests were also performed 6 months after AVF closure (M6). An echocardiographic examination was performed at each time point. All serum creatinine values were collected to compare the individual eGFR slopes before versus after AVF closure. The latest measure of the AVF flow before kidney transplantation was recorded.

Results

Diastolic BP significantly rose from T0 to M12: +4.4±7.3 mm Hg (P = 0.0003) for 24h, +3.8±7.4 mm Hg (P = 0.0018) during the day, and +6.3±9.9 mm Hg (P = 0.0002) during the night, leading to an increased proportion of KTRs with European Society of Hypertension (ESH)-defined arterial hypertension after AVF ligation. No change was observed for systolic BP. NT-proBNP significantly dropped between T0 and M6 (345 [190; 553] to 230 [118; 458] pg/ml, P = 0.0001) and then remained stable from M6 to M12 while suppression of tumorigenicity 2 and galectin-3 levels did not change from T0 to M12. We observed a significant decrease in left ventricular (LV) end-diastolic volume, LV end-systolic volume, LV mass, interventricular septum diameter, left atrial volume, and tricuspid annular plane systolic excursion from T0 to M6 and then a stability from M6 to M12. LV ejection fraction and eGFR slope remained stable during the whole study. These observations remained unchanged after adjustment for AVF flow.

Conclusion

The closure of a patent AVF in KTRs is associated with elevation of diastolic BP, drop in serum NT-proBNP levels, reduction of left ventricular and atrial dimensions, and stability of eGFR slope.

Renal Dysfunction Phenotypes in Patients Undergoing Obesity Surgery

Obesity surgery candidates are at an increased risk of kidney injury, but pre-operative evaluation usually neglects kidney function assessment. This study aimed to identify renal dysfunction in candidates for bariatric surgery. To reduce the sources of bias, subjects with diabetes, prediabetes under metformin treatment, neoplastic or inflammatory diseases were excluded. Patients' (n = 192) average body mass index was 41.7 ± 5.4 kg/m². Among these, 51% (n = 94) had creatinine clearance over 140 mL/min, 22.4% (n = 43) had proteinuria over 150 mg/day and 14.6% (n = 28) albuminuria over 30 mg/day. A creatinine clearance higher than 140 mL/min was associated with higher levels of proteinuria and albuminuria. Univariate analysis identified sex, glycated hemoglobin, uric acid, HDL and VLDL cholesterol as being associated with albuminuria, but not with proteinuria. On multivariate analysis, glycated hemoglobin and creatinine clearance as continuous variables were significantly associated with albuminuria. In summary, in our patient population prediabetes, lipid abnormalities and hyperuricemia were associated with albuminuria, but not with proteinuria, suggesting different disease mechanisms might be implicated. Data suggest that in obesity-associated kidney disease, tubulointerstitial injury precedes glomerulopathy. A significant proportion of obesity surgery candidates present clinically relevant albuminuria and proteinuria along with renal hyperfiltration, suggesting that routine pre-operative assessment of these parameters should be considered.

Extracellular fluid volume: A suitable indexation variable to assess impact of bariatric surgery on glomerular filtration rate in patients with chronic kidney disease

BACKGROUND

Bariatric surgery (BS) might be a nephroprotective treatment in obese patients with chronic kidney disease (CKD), and the non-linear relation between body surface area (BSA) and extracellular fluid volume (ECFV) in obese people raises the question of the most relevant way to scale glomerular filtration rate (GFR) for assessing renal function changes after BS.

METHODS

We screened 1774 BS candidates and analysed 10 consecutive participants with CKD stage 3. True GFR (mGFR), measured by the renal clearance of 51Cr-ethylenediaminetetraacetic acid (EDTA), was scaled either to BSA (mGFRBSA) or to ECFV measured by 51Cr-EDTA distribution volume (mGFRECFV) before and one year after BS.

RESULTS

The 10 candidates for BS had a mean body mass index of 43.3 ± 3.6 kg/m2 and a mean GFR of 48 ± 8 mL/min/1.73 m2. Six participants had a sleeve gastrectomy and four had a Roux-en-Y gastric bypass. One year after BS, ECFV decreased (23.2 ± 6.2 to 17.9 ± 4.3 L, p = 0.001), absolute mGFR was not significantly modified (74 ± 23 versus 68 ±19 mL/min), mGFRBSA did not change significantly (53 ± 18 versus 56 ± 17 mL/min/1.73 m2) whereas mGFRECFV significantly increased (42 ± 13 versus 50 ± 14 mL/min/12.9 L, p = 0.037). The relation between mGFRECFV and mGFRBSA was different from the identity line before (p = 0.014) but not after BS (p = 0.09).

CONCLUSION

There is a difference between mGFRBSA and mGFRECFV following BS and the latter might better reflect the adequacy between renal function and corpulence.

Assessment of kidney function: clinical indications for measured GFR

In the vast majority of cases, glomerular filtration rate (GFR) is estimated using serum creatinine, which is highly influenced by age, sex, muscle mass, body composition, severe chronic illness and many other factors. This often leads to misclassification of patients or potentially puts patients at risk for inappropriate clinical decisions. Possible solutions are the use of cystatin C as an alternative endogenous marker or performing direct measurement of GFR using an exogenous marker such as iohexol. The purpose of this review is to highlight clinical scenarios and conditions such as extreme body composition, Black race, disagreement between creatinine- and cystatin C-based estimated GFR (eGFR), drug dosing, liver cirrhosis, advanced chronic kidney disease and the transition to kidney replacement therapy, non-kidney solid organ transplant recipients and living kidney donors where creatinine-based GFR estimation may be invalid. In contrast to the majority of literature on measured GFR (mGFR), this review does not include aspects of mGFR for research or public health settings but aims to reach practicing clinicians and raise their understanding of the substantial limitations of creatinine. While including cystatin C as a renal biomarker in GFR estimating equations has been shown to increase the accuracy of the GFR estimate, there are also limitations to eGFR based on cystatin C alone or the combination of creatinine and cystatin C in the clinical scenarios described above that can be overcome by measuring GFR with an exogenous marker. We acknowledge that mGFR is not readily available in many centres but hope that this review will highlight and promote the expansion of kidney function diagnostics using standardized mGFR procedures as an important milestone towards more accurate and personalized medicine.

Evaluation of the diagnostic performance of the creatinine-based Chronic Kidney Disease Epidemiology Collaboration equation in people with diabetes: A systematic review

AIMS

GFR estimated with the creatinine-based Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI_Cr ) equation is used to screen for diabetic kidney disease and assess its severity. We systematically reviewed the process and outcome of evaluating CKD-EPI_Cr in estimating point GFR or GFR decline over time in adults with type 1 or type 2 diabetes.

METHODS

In this systematic review, MEDLINE, Embase and Cochrane Central Register of Controlled Trials were searched up to August 2019. Observational studies comparing CKD-EPI_Cr with measured GFR (mGFR) in adults with diabetes were included. Studies on people with kidney transplant, non-diabetes related kidney disease, pregnancy, potential kidney donors, and those with critical or other systematic illnesses were excluded. Two independent reviewers extracted data from published papers and disagreements were resolved by consensus. Risk-of-bias was assessed using the Quality Assessment of Diagnostic Accuracy Studies-2 tool. (PROSPERO registration number: CRD42018108776).

RESULTS

From the 2820 records identified, 29 studies (14 704 participants) were included. All studies were at risk of bias. Bias (eight different forms) ranged from -26 to 35 ml min^-1  1.73 m^-2 ; precision (five different forms) ranged between 9 and 63 ml min^-1  1.73 m^-2 ; accuracy (five different forms) ranged between 16% and 96%; the correlation coefficient between CKD-EPI_Cr and mGFR (four different forms) ranged between 0.38 and 0.86; and the reduced major axis regression slope ranged between 0.8 and 1.8.

CONCLUSIONS

Qualitative synthesis of data suggested CKD-EPI_Cr was inaccurate in estimating point GFR or GFR decline over time. Furthermore, a lack of consistency in the methods and processes of evaluating the diagnostic performance of CKD-EPI_Cr limits reliable quantitative assessment. The equation needs to be improved in adults with diabetes.

The failure of glomerular filtration rate estimating equations among obese population

BACKGROUND

Obesity is a major public health with increasing numbers of obese individuals are at risk for kidney disease. However, the validity of serum creatinine-based glomerular filtration rate (GFR) estimating equations in obese population is yet to be determined.

METHODS

We evaluated the performance of the reexpressed Modification of Diet in Renal Disease (MDRD), reexpressed MDRD with Thai racial factor, Thai estimated GFR (eGFR) as well as Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations among obese patients, defined as body mass index (BMI) ≥25 kg/m2 with the reference measured GFR (mGFR) determined by 99mTc-diethylene triamine penta-acetic acid (99mTc-DTPA) plasma clearance method. Serum creatinine levels were measured using standardized enzymatic method simultaneously with GFR measurement. The statistical methods in assessing agreement for continuous data including total deviation index (TDI), concordance correlation coefficient (CCC), and coverage probability (CP) for each estimating equation were compared with the reference mGFR. Accuracy within 10% representing the percentage of estimations falling within the range of ±10% of mGFR values for all equations were also tested.

RESULTS

A total of 240 Thai obese patients were finally recruited with mean BMI of 31.5 ± 5.8 kg/m2. In the total population, all eGFR equations underestimated the reference mGFR. The average TDI values were 55% indicating that 90% of the estimates falling within the range of -55 to +55% of the reference mGFR. The CP values averaged 0.23 and CCC scores ranged from 0.75 to 0.81, reflecting the low to moderate levels of agreement between each eGFR equation and the reference mGFR. The proportions of patients achieving accuracy 10% ranged from 23% for the reexpressed MDRD equation to 33% for the Thai eGFR formula. Among participants with BMI more than 35 kg/m2 (n = 48), the mean error of all equations was extremely wide and significantly higher for all equations compared with the lower BMI category. Also, the strength of agreement evaluated by TDI, CCC, and CP were low in the subset of patients with BMI ≥35 kg/m2.

CONCLUSION

Estimating equations generally underestimated the reference mGFR in subjects with obesity. The overall performance of GFR estimating equations demonstrated poor concordance with the reference mGFR among individuals with high BMI levels. In certain clinical settings such as decision for dialysis initiation, the direct measurements of GFR are required to establish real renal function among obese population.

Cystatin C: A Primer for Pharmacists

Pharmacists are at the forefront of dosing and monitoring medications eliminated by or toxic to the kidney. To evaluate the effectiveness and safety of these medications, accurate measurement of kidney function is paramount. The mainstay of kidney assessment for drug dosing and monitoring is serum creatinine (SCr)-based estimation equations. Yet, SCr has known limitations including its insensitivity to underlying changes in kidney function and the numerous non-kidney factors that are incompletely accounted for in equations to estimate glomerular filtration rate (eGFR). Serum cystatin C (cysC) is a biomarker that can serve as an adjunct or alternative to SCr to evaluate kidney function for drug dosing. Pharmacists must be educated about the strengths and limitations of cysC prior to applying it to medication management. Not all patient populations have been studied and some evaluations demonstrated large variations in the relationship between cysC and GFR. Use of eGFR equations incorporating cysC should be reserved for drug management in scenarios with demonstrated outcomes, including to improve pharmacodynamic target attainment for antibiotics or reduce drug toxicity. This article provides an overview of cysC, discusses evidence around its use in medication dosing and in special populations, and describes practical considerations for application and implementation.

Severe obesity and the impact of medical weight loss on estimated glomerular filtration rate

OBJECTIVE

To assess the impact of obesity, glucose tolerance, and weight loss on renal function, we measured serum creatinine and cystatin C and estimated glomerular filtration rate (GFR) indexed to 1.73m2 body surface area (BSA) and GFR indexed to actual BSA in subjects with normal and abnormal glucose tolerance before and up to 2 years after medical weight loss.

METHODS

We studied 146 subjects at baseline and 3-to-6 months after 18% reduction in weight; 43 were also studied at 2-years. GFR was estimated using the MDRD, CKD-EPICr, CKD-EPICysCr, and the CKD-EPICys equations.

RESULTS

eGFR was consistently lower when creatinine-based rather than cystatin C-based estimating equations were used. eGFR was lower when creatinine-based or cystatin C-based equations were indexed to 1.73m2 BSA than when they were indexed to actual BSA. eGFR indexed to actual BSA was more likely to demonstrate hyperfiltration (eGFR ≥135 ml/min) than eGFR indexed to 1.73m2 BSA and decreased into the normal range with weight loss. eGFR was highest in subjects with impaired fasting glucose but there was little difference in the patterns of change in eGFR across groups by glucose tolerance status.

CONCLUSIONS

With severe obesity, high fat-free mass and BSA result in low estimates of eGFR indexed to 1.73m2 BSA, especially when creatinine-based estimating equations are used. GFR indexed to actual BSA is approximately 50% higher. When eGFR is indexed to actual BSA, many subjects display evidence of renal hyperfiltration which improves with weight loss. In subjects with severe obesity undergoing medical weight loss, estimating equations that use cystatin C and are indexed to actual BSA may provide a more accurate assessment of renal function.

The Ratio Fallacy, with Special Reference to the Cardiac Index

When comparing cardiac outputs in children of different sizes, or deciding on the normality of these outputs, we often convert the absolute output to the output per m² body surface area-the cardiac index. For small infants, this leads to potentially large errors. The best way to evaluate these outputs is to determine their z values.

The closure of arteriovenous fistula in kidney transplant recipients is associated with an acceleration of kidney function decline

Background

The creation of arteriovenous fistula (AVF) may retard chronic kidney disease progression in the general population. Conversely, the impact of AVF closure on renal function in kidney transplant recipients (KTRs) remains unknown.

Methods

From 2007 to 2013, we retrospectively categorized 285 KTRs into three groups: no AVF (Group 0, n = 90), closed AVF (Group 1, n = 114) and left-open AVF (Group 2, n = 81). AVF closure occurred at 653 ± 441 days after kidney transplantation (KTx), with a thrombosis:ligation ratio of 19:95. Estimated glomerular filtration rate (eGFR) was determined using the Modification of Diet in Renal Disease equation. Linear mixed models calculated the slope and intercept of eGFR decline versus time, starting at 3 months post-KTx, with a median follow-up of 1807 days (95% confidence interval 1665-2028).

Results

The eGFR slope was less in Group 1 (-0.081 mL/min/month) compared with Group 0 (-0.183 mL/min/month; P = 0.03) or Group 2 (-0.164 mL/min/month; P = 0.09). Still, the eGFR slope significantly deteriorated after (-0.159 mL/min/month) versus before (0.038 mL/min/month) AVF closure (P = 0.03). Study periods before versus after AVF closure were balanced to a mean of 13.5 and 12.5 months, respectively, with at least 10 observations per patient ( n = 99).

Conclusions

In conclusion, a significant acceleration of eGFR decline is observed over the 12 months following the closure of a functioning AVF in KTRs.

Prevalence of and factors associated with renal dysfunction in rheumatoid arthritis patients: a cross-sectional study in community hospitals

This study was designed to determine the prevalence of renal dysfunction in rheumatoid arthritis (RA) patients and to identify factors associated with this complication. Between October 2014 and May 2015, we consecutively recruited RA patients at rheumatology sections of community hospitals in Japan. Each patient's absolute and body surface area (BSA)-indexed estimated glomerular filtration rate (eGFR) values were measured twice over a 3-month interval. Renal dysfunction was defined as absolute eGFR or BSA-indexed eGFR < 60. Albuminuria and hematuria were also recorded. Associations between renal dysfunction and possible risk factors were examined by multivariate logistic regression analyses. A total of 1908 outpatients with RA were included in this study. The prevalence of renal dysfunction based on absolute eGFR and BSA-indexed eGFR was 33.8 and 18.6%, respectively. Albuminuria was observed in 8.1% of this patient cohort, and the prevalence of hematuria was 7.5%. Advanced age (odds ratio [OR] 7.24, p < 0.001), female sex (OR 3.12, p < 0.001), hypertension (OR 2.22, p < 0.001), and obesity (OR 0.59, p < 0.001) were independently associated with the risk of absolute eGFR-based renal dysfunction. Advanced age (OR 5.19, p < 0.001) and hypertension (OR 3.05, p < 0.001) also had associations with BSA-indexed eGFR-based renal dysfunction. RA duration, stages, severity, and cumulative steroid dose were considered significant risk factors in univariate analyses, but their associations were less potent after adjustment for other covariates. Renal dysfunction is relatively common in RA patients and is mainly associated with advanced age and hypertension but not with RA-related factors.

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.

Short- and long-term results of radial artery and saphenous vein grafts in the right coronary system: a propensity-matched study

PURPOSE

The selection of optimal grafts for the right coronary artery remains controversial. This study aims to evaluate the short- and long-term results of radial artery (RA) grafts and saphenous vein grafts (SVGs) to the right coronary artery.

METHODS

We reviewed, retrospectively, isolated coronary artery bypass grafts, placed between 1997 and 2007, and compared the long-term results of patients who received RA (n = 110) grafts with those of patients who received SVGs (n = 264) using propensity-score matching for risk. The preoperative predictors of graft occlusion were investigated on a per case basis.

RESULTS

Superior survival was noted in the unmatched RA group, but late outcomes after propensity-score matching yielded 91 patient pairs that were similar in the two groups. Graft failure was not correlated with mortality, but showed strong correlation with cardiac events in all patients. The predictors of graft occlusion in the RA group were mild proximal stenosis and low indexing glomerular filtration rates for body surface area, whereas those in the SVG were female gender and off-pump coronary artery bypass grafting.

CONCLUSIONS

There were no significant differences in long-term outcomes between the RA and SVG groups. Predictors of graft occlusion differed between the groups. Notably, renal dysfunction impaired radial patency, emphasizing the importance of careful graft selection.

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.

Obesity-related glomerulopathy: clinical and pathologic characteristics and pathogenesis

The prevalence of obesity-related glomerulopathy is increasing in parallel with the worldwide obesity epidemic. Glomerular hypertrophy and adaptive focal segmental glomerulosclerosis define the condition pathologically. The glomerulus enlarges in response to obesity-induced increases in glomerular filtration rate, renal plasma flow, filtration fraction and tubular sodium reabsorption. Normal insulin/phosphatidylinositol 3-kinase/Akt and mTOR signalling are critical for podocyte hypertrophy and adaptation. Adipokines and ectopic lipid accumulation in the kidney promote insulin resistance of podocytes and maladaptive responses to cope with the mechanical forces of renal hyperfiltration. Although most patients have stable or slowly progressive proteinuria, up to one-third develop progressive renal failure and end-stage renal disease. Renin-angiotensin-aldosterone blockade is effective in the short-term but weight loss by hypocaloric diet or bariatric surgery has induced more consistent and dramatic antiproteinuric effects and reversal of hyperfiltration. Altered fatty acid and cholesterol metabolism are increasingly recognized as key mediators of renal lipid accumulation, inflammation, oxidative stress and fibrosis. Newer therapies directed to lipid metabolism, including SREBP antagonists, PPARα agonists, FXR and TGR5 agonists, and LXR agonists, hold therapeutic promise.

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.

[Dosing adjustment and renal function: Which equation(s)?]

While the CKD-EPI (for Chronic Kidney Disease Epidemiology) equation is now implemented worldwide, utilization of the Cockcroft formula is still advocated by some physicians for drug dosage adjustment. Justifications for this recommendation are that the Cockcroft formula was preferentially used to determine dose adjustments according to renal function during the development of many drugs, better predicts drugs-related adverse events and decreases the risk of drug overexposure in the elderly. In this opinion paper, we discuss the weaknesses of the rationale supporting the Cockcroft formula and endorse the French HAS (Haute Autorité de santé) recommendation regarding the preferential use of the CKD-EPI equation. When glomerular filtration rate (GFR) is estimated in order to adjust drug dosage, the CKD-EPI value should be re-expressed for the individual body surface area (BSA). Given the difficulty to accurately estimate GFR in the elderly and in individuals with extra-normal BSA, we recommend to prescribe in priority monitorable drugs in those populations or to determine their "true" GFR using a direct measurement method.

The performance of contemporary cystatin C-based GFR equations in predicting gentamicin clearance

AIMS

We aimed to compare the performances of contemporary cystatin C (Cys)-based GFR equations, and the creatinine only Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation for predicting gentamicin clearance.

METHODS

The bias and imprecision of the CKD-EPI, CKD-EPI_Cys and creatinine-cystatin C CKD-EPI (CKD-EPI_CrCys) equations for predicting gentamicin clearances, were assessed in 260 patients treated with gentamicin during 2012-2013. The creatinine-cystatin C Berlin Initiative Study equation (BIS_CrCys) was examined in the ≥70 year subgroup. The reference gentamicin clearance was calculated using post-dose plasma concentrations.

RESULTS

The CKD-EPI_CrCys equation had the highest percentage of estimates within 30% of the reference gentamicin clearance (70%, P = 0.003) and lowest root mean square error (95% CI) of 29 (25, 23) ml min(-1) of the three equations for the entire cohort. There was no significant improvement in the performances of the equations with the exclusion of 41 patients with abnormal thyroid function tests or steroid co-prescription at the time of the index gentamicin dose. Of the remaining 219 patients, adjustment for individual BSA improved the performances of all GFR equations (P ≤ 0.003) in those with body mass indices (BMI) <18.5 or ≥30 kg m(-2) , but not those with BMI 18.5-29.9 kg m(-2) . There was no advantage of the BIS_CrCys over the CKD-EPI_CrCys equation in the ≥70 year subgroup.

CONCLUSIONS

The CKD-EPI_CrCys equation provided the best estimate of gentamicin clearance. If used for guiding gentamicin dosing, the results from GFR equations should be adjusted for individual BSA at the extremes of body size.

Smoking and renal function in people living with human immunodeficiency virus: a Danish nationwide cohort study

INTRODUCTION

Smoking is a main risk factor for morbidity and mortality in people living with human immunodeficiency virus (PLHIV), but its potential association with renal impairment remains to be established.

METHODS

We did a nationwide population-based cohort study in Danish PLHIV to evaluate the association between smoking status and 1) overall renal function and risk of chronic kidney disease (CKD), 2) risk of any renal replacement therapy (aRRT), and 3) mortality following aRRT. We calculated estimated creatinine clearance using the Cockcroft-Gault equation (CG-CrCl), and evaluated renal function graphically. We calculated cumulative incidence of CKD (defined as two consecutive CG-CrCls of ≤60 mL/min, ≥3 months apart) and aRRT and used Cox regression models to calculate incidence rate ratios (IRRs) for risk of CKD, aRRT, and mortality rate ratios (MRRs) following aRRT.

RESULTS

From the Danish HIV Cohort Study, we identified 1,475 never smokers, 768 previous smokers, and 2,272 current smokers. During study period, we observed no association of smoking status with overall renal function. Previous and current smoking was not associated with increased risk of CKD (adjusted IRR: 1.1, 95% confidence interval [CI]: 0.7-1.7; adjusted IRR: 1.3, 95% CI: 0.9-1.8) or aRRT (adjusted IRR: 0.8, 95% CI: 0.4-1.7; adjusted IRR: 0.9, 95% CI: 0.5-1.7). Mortality following aRRT was high in PLHIV and increased in smokers vs never smokers (adjusted MRR: 3.8, 95% CI: 1.3-11.2).

CONCLUSION

In Danish PLHIV, we observed no strong association between smoking status and renal function, risk of CKD, or risk of aRRT, but mortality was increased in smokers following aRRT.

Hyperfiltration in Indigenous Australians with and without diabetes

BACKGROUND

Hyperfiltration (HF) has been linked to the development of diabetic kidney disease (DKD), but the causative or predictive role of HF in the pathogenesis of DKD still remains unclear. To date, there have been no studies of HF in Indigenous Australians, a population with high rates of both diabetes and end-stage kidney disease. We aimed to compare the characteristics and frequency of HF in Indigenous Australians with and without type 2 diabetes.

METHODS

Indigenous Australian participants, recruited across five pre-defined strata of health, diabetes status and kidney function, had a reference glomerular filtration rate (GFR) measured using plasma disappearance of iohexol [measured GFR(mGFR)] over 4 h. HF was defined in various ways: (i) mGFR > 144 mL/min/1.73 m(2), which is mGFR > 1.96 × SD above the mean of the mGFR in non-diabetic participants with normal albuminuria and normal renal function (mGFR > 90 mL/min/1.73 m(2)); (ii) age-corrected mGFR (>144 mL/min/1.73 m(2)) to account for the effect of ageing on GFR in subjects over 40 years of age with cut-off 1 mL/min/1.73 m(2) lower for every year; (iii) mGFR > 144 mL/min, without correction for body surface area or age, as well as (iv) mGFR > 125 mL/min/1.73 m(2), without adjustment for age.

RESULTS

A total of 383 Indigenous participants, 125 with and 258 without diabetes, with mGFR > 90 mL/min/1.73 m(2) were studied. The proportion of participants with HF was 7% using mGFR > 144 mL/min/1.73 m(2), 11% using the age-adjusted definition, 19% using mGFR > 144 mL/min and 27% using mGFR > 125 mL/min/1.73 m(2). Diabetes was more common in participants with HF (40-74%) compared with normofiltering participants (28-31%), regardless of the definition of HF.

CONCLUSIONS

HF exists in Indigenous Australians with and without diabetes. A greater proportion of participants had diabetes in HF group compared with normofiltration group. Long-term follow-up of this cohort is necessary to determine if HF plays a role in the development of DKD and non-DKD.

Prevalence of Renal Impairment in Palliative Care Inpatients: A Retrospective Analysis

BACKGROUND AND OBJECTIVE

Multiple drugs used in palliative care, including most opioids or their active metabolites may accumulate in patients with abnormal renal function, leading to serious adverse effects. The incidence and severity of renal impairment in palliative care inpatients has not been evaluated. The aim of the study was to investigate the incidence and severity of renal impairment in palliative care inpatients.

METHODS

A retrospective analysis of medical records of patients admitted to the palliative care ward was performed. Estimated glomerular filtration rate (eGFR) was derived using the Cockcroft-Gault (C-G) and abbreviated Modification of Diet in Renal Disease (aMDRD) equations.

RESULTS

Serum creatinine levels (SCr) were determined in 332 subjects aged 66.4±11.80 years (194 women; mean body mass index [BMI] 22.7±5.21 kg/m(2)). Mean SCr was 107.7±112.31 μmol/L. Elevated SCr (>115 μmol/L) was found in 20.2% of patients. Mean eGFR calculated with C-G and aMDRD equations was 66.6±38.52 mL/min and 78.7±43.55 mL/min/1.73 m(2), respectively. Between 35.2% and 51.8% of patients had eGFR <60 mL/min/1.73 m(2) (depending on the equation used). More than 10% of patients had eGFR <30 mL/min/1.73 m(2). In patients with normal SCr, between 18.9% and 39.2% had eGFR <60 mL/min/1.73 m(2).

CONCLUSION

Renal impairment is common in palliative care inpatients, including considerable number of subjects with moderately to severely reduced kidney function.

Differential scaling of glomerular filtration rate and ingested metabolic burden: implications for gender differences in chronic kidney disease outcomes

BACKGROUND

Men commence dialysis with a higher estimated glomerular filtration rate (eGFR) than women and are more likely to transition from chronic kidney disease (CKD) to end-stage renal disease. We hypothesized that for a given estimated body surface area (BSA) men have a greater metabolic burden, and that consequently, the practice of indexing GFR to BSA results in gender differences in the degree of biochemical uraemia.

METHODS

Metabolic burden was assessed as estimated dietary protein, calorie, phosphorus, sodium and potassium intakes and urinary urea nitrogen excretion in the Chronic Renal Insufficiency Cohort, Modification of Diet in Renal Disease study, and National Health and Nutrition Examinations Surveys (NHANES) 1999-2010. Uraemia was characterized by serum biochemistry.

RESULTS

Per m(2) BSA, men had greater urea nitrogen excretion and intakes of all dietary parameters (P < 0.001 for all). For a given BSA-indexed iothalamate GFR or eGFR, male gender was associated with a 10-15% greater serum urea nitrogen (P < 0.001), giving men with a BSA-indexed GFR of 70-75 mL/min/1.73 m(2) the same serum urea nitrogen concentration as women with a GFR of 60 mL/min/1.73 m(2). However, indexing metabolic burden and GFR to alternative body size measures (estimated total body water, lean body mass or resting energy expenditure) abolished/reversed the gender associations. In NHANES, BSA-indexed eGFR distribution was very similar for men and women, so that adjusting for eGFR had little effect on the gender difference in serum urea.

CONCLUSIONS

Indexing GFR to BSA across genders may approximate nature's indexing approach, but gives men a greater ingested burden of protein, calories, sodium, phosphorus and potassium per mL/min GFR. This has implications for gender differences in CKD outcomes.

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.

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.

Predictors of advanced chronic kidney disease and end-stage renal disease in HIV-positive persons

OBJECTIVES

Whilst several antiretroviral drugs have been associated with moderate chronic kidney disease (CKD), their contribution to advanced CKD and end-stage renal disease (ESRD) remain unknown.

DESIGN

D:A:D participants with at least three estimated glomerular filtration rates (eGFR) after February 2004 were followed until the first of advanced CKD (confirmed eGFR ≤ 30 ml/min, ≥3 months apart), ESRD (dialysis ≥3 months/ transplantation), 6 months after last visit or February 2012.

METHODS

Poisson regression was used to assess risk factors for advanced CKD/ESRD including exposure to potential nephrotoxic antiretroviral drugs and antiretroviral drug discontinuation rates according to latest eGFR.

RESULTS

Among 35 192 persons contributing 200 119 person years of follow-up (PYFU), 135 (0.4%) developed advanced CKD (n = 114)/ESRD (n = 21); incidence rate = 0.67 [95% confidence interval (CI), 0.56-0.79]/1000 PYFU. Tenofovir (TDF) was particularly frequently discontinued as eGFR declined. After adjustment, those previously exposed but currently off TDF had similar advanced CKD/ESRD rate ratios compared with those unexposed [1.00 (95% CI, 0.66-1.51)], while those currently on TDF had reduced rates [0.23 (95% CI, 0.13-0.41)]. No consistent associations with other antiretroviral drugs were seen. Results were robust after time-lagging antiretroviral drug exposure, stratifying by baseline eGFR, and allowing for competing risks. Other predictors were diabetes, hypertension, baseline eGFR, smoking and current CD4 cell count. The incidence rate in nonsmokers with baseline eGFR > 60 and no diabetes or hypertension was 0.16 (95% CI 0.09-0.26)/1000 PYFU.

CONCLUSION

Neither current nor recent antiretroviral drug use predicted advanced CKD/ESRD during 6 years median follow-up in a large, heterogenenous and primarily white cohort. TDF discontinuation rates increased with decreasing eGFR, leaving a selected group still on TDF at lower advanced CKD/ESRD risk. Traditional renal risk factors and current CD4 cell count were the strongest advanced CKD/ESRD predictors.

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.

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.

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.

Modification of Diet in Renal Disease versus Chronic Kidney Disease Epidemiology Collaboration equation to estimate glomerular filtration rate in obese patients

BACKGROUND

Obesity is a recognized risk factor for both the development and progression of chronic kidney disease (CKD). Accurate estimation of glomerular filtration rate (GFR) is thus important in these patients. We tested the performances of two creatinine-based GFR estimates, the Modification of Diet in Renal Disease (MDRD) and the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations, in an obese population.

METHODS

Patients with body mass index (BMI) > 30 kg/m(2) were included. The reference method for measured GFR (mGFR) was (51)Cr-EDTA (single-injection method, two blood samples at 120 and 240 min). Both indexed and non-indexed results were considered. Serum creatinine was measured using the IDMS-traceable compensated Jaffe method. Mean bias (eGFR-mGFR), precision (SD around the bias) and accuracy within 30% (percentage of estimations within 30% of mGFR) were calculated for both equations.

RESULTS

The population included 366 patients (185 women) from two different areas. Mean age was 55 ± 14 years, and mean BMI was 36 ± 7 kg/m(2). Mean mGFR was 56 ± 26 mL/min/1.73 m(2) (71 ± 35 mL/min without indexation). In the total population, mean bias was +1.9 ± 14.3 and +4.6 ± 14.7 mL/min/1.73 m(2) (P < 0.05), and accuracy 30% was 80 and 76% for the MDRD and CKD-EPI equations (P < 0.05), respectively. In patients with mGFR > 60 mL/min/1.73 m(2), mean bias was +4.6 ± 18.4 and +9.3 ± 17.2 mL/min/1.73 m(2) (P < 0.05), and accuracy 30% was 81 and 79% (NS) for the MDRD and CKD-EPI equations, respectively.

CONCLUSIONS

The CKD-EPI equation did not outperform the MDRD study equation in this population of obese patients.

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.

Normal reference values for glomerular filtration rate: what do we really know?

In nephrology, chronic kidney disease is defined by both proteinuria and measurement of glomerular filtration rate (GFR). This article focuses on GFR and different ways to define its normal reference values. In this context, we compare two perspectives: first the reference values defined by measuring GFR in normal individuals (the 'classical way') and secondly a fixed cut-off value at 60 mL/min/1.73 m2 according to the associated mortality risk (the 'prognostic way'). Following the classical way, we can assert that normal GFR values are largely over 60 mL/min/1.73 m2 in healthy subjects, at least before the age of 70 years. However, we know that GFR physiologically decreases with age, and in adults older than 70 years, values below 60 mL/min/1.73 m2 could be considered normal. Following the 'prognostic way', the fixed cut-off of 60 mL/min/1.73 m2 has been retained in the K-DIGO guidelines. However, we challenge this concept and the fact that the variable 'age' is poorly taken into account in these data. There is an obvious discrepancy between the reference values defined either by the 'classical way' or by the 'prognostic way' which we think could be largely reduced, if age was better taken into consideration in these definitions.

Body mass index and acute kidney injury in the acute respiratory distress syndrome

OBJECTIVES

Obesity is increasingly encountered in intensive care units but the relationship between obesity and acute kidney injury is unclear. We aimed to evaluate whether body mass index was associated with acute kidney injury in the acute respiratory distress syndrome and to examine the association between acute kidney injury and mortality in patients with and without obesity.

DESIGN

Retrospective study.

SETTING

Massachusetts General Hospital and Beth Israel Deaconess Medical Center.

PATIENTS

Seven hundred fifty-one patients with acute respiratory distress syndrome.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Acute kidney injury was defined as meeting the "Risk" category according to modified Risk, Injury, Failure, Loss, End-stage criteria based on creatinine and glomerular filtration rate because urine output was only available on the day of intensive care unit admission. Body mass index was calculated from height and weight at intensive care unit admission. The prevalence of acute kidney injury increased significantly with increasing weight (p = .01). The odds of acute kidney injury were twice in obese and severely obese patients compared to patients with normal body mass index, after adjusting for predictors of acute kidney injury (age, diabetes, Acute Physiology and Chronic Health Evaluation III, aspiration, vasopressor use, and thrombocytopenia [platelets ≤ 80,000/mm]). After adjusting for the same predictors, body mass index was significantly associated with acute kidney injury (odds ratio(adj) 1.20 per 5 kg/m increase in body mass index, 95% confidence interval 1.07-1.33). On multivariate analysis, acute kidney injury was associated with increased acute respiratory distress syndrome mortality (odds ratio(adj) 2.76, 95% confidence interval 1.72-4.42) whereas body mass index was associated with decreased mortality (odds ratio(adj) 0.81 per 5 kg/m increase in body mass index, 95% confidence interval 0.71-0.93) after adjusting for mortality predictors.

CONCLUSIONS

In acute respiratory distress syndrome patients, obesity is associated with increased development of acute kidney injury, which is not completely explained by severity of illness or shock. Although increased body mass index is associated with decreased mortality, acute kidney injury remained associated with higher mortality even after adjusting for body mass index.

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 Influence of Body Size Descriptors on the Estimation of Kidney Function in Normal Weight, Overweight, Obese, and Morbidly Obese Adults

Background:

Dosing adjustments for patients with impaired kidney function are often based on estimated creatinine clearance (eCrCI) because measuring kidney (unction is not always possible for dose adjustment. However, there is no consensus on the body size descriptor that should be used in the estimation equations.

Objective:

To compare the use of alternative body size descriptors (ABSDs) on the performance of kidney function estimation equations compared with measured CrCI (mCrCI).

Methods:

We combined 2 data sources with mCrCI: a Food and Drug Administration clinical trial database that includes subjects with body mass index (BMI) less than 40 kg/m2 and published data from those 40 kg/m2 or more. The 3 parent equations (Cockcroft-Gault [CG], Modification of Diet in Renal Disease [MDRD], Chronic Kidney Disease-Epidemiology Collaboration [CKDEPI]), and 14 ABSD-modilied equations were compared with mCrCI for accuracy, bias, agreement, goodness of (it (R2). and prediction error. These equations were also compared across mCrCI and BMI strata.

Results:

Subjects (n = 590) were aged 19–80 years; 33.9% were female and BMI ranged from 17.2 to 95.6 kg/m2. Compared with mCrCI, the use of total weight in the CG equation yielded low accuracy (12.5%) and significant bias (–107 mL/min) in the morbidly obese group. In contrast, the use of lean body weights (BMI ≥40 kg/m2) and total ± adjusted weights (BMI <40 kg/m2) with the CG equation yielded higher accuracy, greater than or equal to 60.7% across all BMI strata, and was unbiased. Transforming the MDRD or CKDEPI equations with body surface area improved accuracy only at mCrCI of 30–80 mL/min and increased the overall prediction error.

Conclusions:

No kidney function equation was consistently accurate and unbiased across weight, mCrCI. and estimate ranges. The accuracy and over-estimation bias of the CG equation in obese subjects was improved through the selective use of total, adjusted, and lean body weight by BMI strata.

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.

The Cockcroft-Gault: a better predictor of renal function in an overweight and obese diabetic population

BACKGROUND

The performance of the Cockcroft-Gault (CG) equation, the Modification of Diet in Renal Disease (MDRD) formula, and the Chronic Kidney Disease Epidemiology Collaboration equation (CKD-EPI) was evaluated in body mass index (BMI) categories.

MATERIAL AND METHODS

In this retrospective cohort study in diabetic patients, creatinine clearance was measured by collecting 24-hour urines. Renal function was estimated using the CG, MDRD, and CKD-EPI. The performance of the equations was evaluated using correlation, Krippendorff's coefficient, bias, precision, and accuracy.

RESULTS

The bias of the MDRD and CKD-EPI increased from -13.9 ml/min/1.73 m(2) and -14.0 ml/min/1.73 m(2) (BMI < 25 kg/m(2)), respectively, to -31.7 ml/min/1.73 m(2) and -29.6 ml/min/1.73 m(2) (BMI > 30 kg/m(2)), respectively. Bias of the CG decreased from -13.4 ml/min (BMI < 25 kg/m(2)) to -3.2 ml/min (BMI > 30 kg/m(2)). With an accepted 30% dispersion, CG had the largest accuracy in the overweight and obese group (76.9 and 76.8%, respectively). The MDRD and CKD-EPI had an accuracy of 45.8 and 34.0% (overweight group), respectively,and 51.9 and 37.3% (obese group), respectively.

CONCLUSIONS

All renal function prediction equations are biased when used in overweight or obese diabetic populations with preserved renal function. The CG provides the best estimate of kidney function. The limitations of renal function prediction equations should be kept in mind when making clinical decisions.

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.