A systematic review of glomerular hyperfiltration assessment and definition in the medical literature

New insights on glomerular hyperfiltration: a Japanese autopsy study

It has been suggested that low nephron number contributes to glomerular hypertension and hyperperfusion injury in progressive chronic kidney disease (CKD). The incidence of CKD in Japan is among the highest in the world, but the reasons remain unclear. We estimated total nephron (glomerular) number (NglomTOTAL) as well as numbers of nonsclerosed (NglomNSG) and globally sclerosed glomeruli (NglomGSG), and the mean volume of nonsclerosed glomeruli (VglomNSG) in Japanese normotensive, hypertensive, and CKD subjects and investigated associations between these parameters and estimated glomerular filtration rate (eGFR). Autopsy kidneys from age-matched Japanese men (9 normotensives, 9 hypertensives, 9 CKD) had nephron number and VglomNSG estimated using disector/fractionator stereology. Subject eGFR, single-nephron eGFR (SNeGFR), and the ratio SNeGFR/VglomNSG were calculated. NglomNSG in Japanese with hypertension (392,108 ± 87,605; P < 0.001) and CKD (268,043 ± 106,968; P < 0.001) was less than in normotensives (640,399 ± 160,016). eGFR was directly correlated with NglomNSG (r = 0.70, P < 0.001) and inversely correlated with VglomNSG (r = -0.53, P < 0.01). SNeGFR was higher in hypertensives than normotensives (P = 0.03), but was similar in normotensives and CKD, while the ratio SNeGFR/VglomNSG was similar in normotensives and hypertensives but markedly reduced in CKD. Nephron number in Japanese with hypertension or CKD was low. This results in a higher SNeGFR in hypertensives compared with normotensive and CKD subjects, but lowered SNeGFR/VglomNSG in CKD subjects, suggesting that changes in GFR are accommodated by glomerular hypertrophy rather than glomerular hypertension. These findings suggest glomerular hypertrophy is a dominant factor in maintenance of GFR under conditions of low nephron number.

Establishing the presence or absence of chronic kidney disease: Uses and limitations of formulas estimating the glomerular filtration rate

The development of formulas estimating glomerular filtration rate (eGFR) from serum creatinine and cystatin C and accounting for certain variables affecting the production rate of these biomarkers, including ethnicity, gender and age, has led to the current scheme of diagnosing and staging chronic kidney disease (CKD), which is based on eGFR values and albuminuria. This scheme has been applied extensively in various populations and has led to the current estimates of prevalence of CKD. In addition, this scheme is applied in clinical studies evaluating the risks of CKD and the efficacy of various interventions directed towards improving its course. Disagreements between creatinine-based and cystatin-based eGFR values and between eGFR values and measured GFR have been reported in various cohorts. These disagreements are the consequence of variations in the rate of production and in factors, other than GFR, affecting the rate of removal of creatinine and cystatin C. The disagreements create limitations for all eGFR formulas developed so far. The main limitations are low sensitivity in detecting early CKD in several subjects, e.g., those with hyperfiltration, and poor prediction of the course of CKD. Research efforts in CKD are currently directed towards identification of biomarkers that are better indices of GFR than the current biomarkers and, particularly, biomarkers of early renal tissue injury.

Combining new tools to assess renal function and morphology: a holistic approach to study the effects of aging and a congenital nephron deficit

Recently, new methods for assessing renal function in conscious mice (transcutaneous assessment) and for counting and sizing all glomeruli in whole kidneys (MRI) have been described. In the present study, these methods were used to assess renal structure and function in aging mice, and in mice born with a congenital low-nephron endowment. Age-related nephron loss was analyzed in adult C57BL/6 mice (10-50 wk of age), and congenital nephron deficit was assessed in glial cell line-derived neurotrophic factor heterozygous (GDNF HET)-null mutant mice. Renal function was measured through the transcutaneous quantitation of fluorescein isothiocyanate-sinistrin half-life (t_1/2) in conscious mice. MRI was used to image, count, and size cationic-ferritin labeled glomeruli in whole kidneys ex vivo. Design-based stereology was used to validate the MRI measurements of glomerular number and mean volume. In adult C57BL/6 mice, older age was associated with fewer and larger glomeruli, and a rightward shift in the glomerular size distribution. These changes coincided with a decrease in renal function. GNDF HET mice had a congenital nephron deficit that was associated with glomerular hypertrophy and exacerbated by aging. These findings suggest that glomerular hypertrophy and hyperfiltration are compensatory processes that can occur in conjunction with both age-related nephron loss and congenital nephron deficiency. The combination of measurement of renal function in conscious animals and quantitation of glomerular number, volume, and volume distribution provides a powerful new tool for investigating aspects of renal aging and functional changes.

Metabolic risk factors in nondiabetic adolescents with glomerular hyperfiltration

BACKGROUND

In adults, glomerular hyperfiltration is associated with abnormalities related to metabolic syndrome (MetS). We investigated if glomerular hyperfiltration was associated with metabolic abnormalities in US adolescents without diabetes.

METHODS

We analyzed data from the National Health and Nutrition Examination Survey, a nationally representative sample of US adolescents ages 12-17 years. Estimated glomerular filtration rate (eGFR) was determined using the bedside Schwartz equation; adolescents with hyperfiltration (eGFR >120 mL/min/1.73 m 2 ) were compared to those with normal eGFR (90-120 mL/min/1.73 m 2 ). We calculated mean levels of factors related to MetS, insulin resistance and diabetes risk, adjusting for age, race/ethnicity, sex, socioeconomic status, and BMI z -score.

RESULTS

Overall, 11.8% of US adolescents had hyperfiltration [95% confidence interval (CI) 10.6-13.0]. Hyperfiltration prevalence varied by race (20.2% in Hispanics versus 9.8% non-Hispanic whites and 7.4% non-Hispanic blacks; P< 0.001). Compared to those with normal eGFR, adolescents with hyperfiltration had higher adjusted mean levels of triglyceride (83 versus 77 mg/dL; P = 0.05), fasting insulin (15.1 versus 12.9; P< 0.001) and homeostatic model assessment of insulin resistance (3.52 versus 3.01; P = 0.001). These differences persisted after adjusting for BMI z- score. Adolescents with hyperfiltration had increased odds for hypertriglyceridemia [odds ratio 1.58 (95% CI 1.11-2.23)]. These relationships varied by racial/ethnic group.

CONCLUSIONS

Glomerular hyperfiltration is associated with hypertriglyceridemia and increased insulin resistance independent of BMI z- score in a nationally representative sample of US adolescents. Hispanic adolescents are more likely to have hyperfiltration than other racial/ethnic groups. These findings could have significance in evaluations of renal function and MetS in adolescents to identify related risks and target interventions.

Association of pre-operative estimated GFR on post-operative pulmonary complications in laparoscopic surgeries

Despite a large body of evidence showing the pandemic of chronic kidney disease, the impact of pre-operative kidney function on the risk of post-operative pulmonary complications (PPCs) is not well known. We used multivariable logistic regression analyses with 3-level hierarchical adjustments to identify the association of pre-operative estimated glomerular filtration rate (eGFR) with PPCs in laparoscopic surgeries. Among 452,213 patients between 2005 and 2013 in the American College of Surgeons National Surgical Quality Improvement Program (ACS-NSQIP) Database, a total of 3,727 patients (0.9%) experienced PPCs. We found a gradient association between lower eGFR and higher likelihood of PPCs in the unadjusted model. In the case-mix adjusted model, a reverse-J-shaped association was observed; a small albeit significant association with the highest eGFR category emerged. Further adjustment slightly attenuated these associations, but the PPCs risk in the eGFR groups of <30, 30-60, and ≥120 mL/min/1.73 m2 remained significant: odds ratios (95% confidence intervals) of 1.82 (1.54-2.16), 1.38 (1.24-1.54), and 1.28 (1.07-1.53), respectively (reference: 90-120 mL/min/1.73 m2). Our findings propose a need for careful pre-operative evaluation of cardiovascular and pulmonary functions and post-operative fluid management among patients with not only lower but also very high eGFR.

How to use… serum creatinine, cystatin C and GFR

Glomerular filtration rate (GFR) is the best overall measure of kidney function. The GFR is relatively low at birth but increases through infancy and early childhood to reach adult levels of approximately 120 mL/min/1.73 m² by age 2. While GFR can be measured most accurately by the urinary clearance of an exogenous ideal filtration marker such as inulin, it is more clinically useful to estimate GFR using a single serum measurement of an endogenous biomarker such as creatinine or cystatin C. When in steady state, there is an inverse relationship between creatinine/cystatin C and GFR, allowing GFR to be estimated from either using simple equations. Because of the non-linear relationship between creatinine/cystatin C and GFR, relatively small initial increases in these markers represent significant decreases in GFR. While cystatin C is produced by all nucleated cells, creatinine is a waste product of muscle metabolism and is therefore influenced by diet and muscle mass/body habitus. Decreased GFR is used to diagnose and stage chronic kidney disease (CKD) using the Kidney Disease: Improving Global Outcomes system. A diagnosis of CKD requires GFR <60 mL/min/1.73 m² for more than 3 months; higher GFR also represents CKD if evidence of kidney damage (such as albuminuria or abnormal imaging) is present. Changes in serum creatinine and urine output are used to diagnose acute kidney injury. It is possible to calculate a kinetic GFR when the creatinine is changing rapidly, though more complex calculations are required.

Glomerular Hyperfiltration in Diabetes: Mechanisms, Clinical Significance, and Treatment

An absolute, supraphysiologic elevation in GFR is observed early in the natural history in 10%-67% and 6%-73% of patients with type 1 and type 2 diabetes, respectively. Moreover, at the single-nephron level, diabetes-related renal hemodynamic alterations-as an adaptation to reduction in functional nephron mass and/or in response to prevailing metabolic and (neuro)hormonal stimuli-increase glomerular hydraulic pressure and transcapillary convective flux of ultrafiltrate and macromolecules. This phenomenon, known as glomerular hyperfiltration, classically has been hypothesized to predispose to irreversible nephron damage, thereby contributing to initiation and progression of kidney disease in diabetes. However, dedicated studies with appropriate diagnostic measures and clinically relevant end points are warranted to confirm this assumption. In this review, we summarize the hitherto proposed mechanisms involved in diabetic hyperfiltration, focusing on ultrastructural, vascular, and tubular factors. Furthermore, we review available evidence on the clinical significance of hyperfiltration in diabetes and discuss currently available and emerging interventions that may attenuate this renal hemodynamic abnormality. The revived interest in glomerular hyperfiltration as a prognostic and pathophysiologic factor in diabetes may lead to improved and timely detection of (progressive) kidney disease, and could provide new therapeutic opportunities in alleviating the renal burden in this population.

Hyperfiltration-associated biomechanical forces in glomerular injury and response: Potential role for eicosanoids

Hyperfiltration is a well-known risk factor in progressive loss of renal function in chronic kidney disease (CKD) secondary to various diseases. A reduced number of functional nephrons due to congenital or acquired cause(s) results in hyperfiltration in the remnant kidney. Hyperfiltration-associated increase in biomechanical forces, namely pressure-induced tensile stress and fluid flow-induced shear stress (FFSS) determine cellular injury and response. We believe the current treatment of CKD yields limited success because it largely attenuates pressure-induced tensile stress changes but not the effect of FFSS on podocytes. Studies on glomerular podocytes, tubular epithelial cells and bone osteocytes provide evidence for a significant role of COX-2 generated PGE₂ and its receptors in response to tensile stress and FFSS. Preliminary observations show increased urinary PGE₂ in children born with a solitary kidney. FFSS-induced COX2-PGE₂-EP₂ signaling provides an opportunity to identify targets and, for developing novel agents to complement currently available treatment.

Association of Increasing GFR with Change in Albuminuria in the General Population

BACKGROUND AND OBJECTIVES

Hyperfiltration at the single-nephron level has been proposed as an early stage of kidney dysfunction of different origins. Evidence supporting this hypothesis in humans is lacking, because there is no method of measuring single-nephron GFR in humans. However, increased whole-kidney GFR in the same individual implies an increased single-nephron GFR, because the number of nephrons does not increase with age. We hypothesized that an increase in GFR would be associated with an increased albumin-to-creatinine ratio in a cohort of the general population.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We measured GFR by iohexol clearance at baseline in 2007-2009 and follow-up after 5.6 years in a representative sample of 1246 persons (aged 50-62 years) who were nondiabetic from the general population of Tromso, northern Norway. Participants were without cardiovascular disease, kidney disease, or diabetes at baseline. We investigated the association between change in GFR and change in albumin-to-creatinine ratio. Increased GFR was defined as a positive change in GFR (change in GFR>0 ml/min) from baseline to follow-up. An albumin-to-creatinine ratio >30 mg/g was classified as albuminuria.

RESULTS

Change in GFR was positively associated with a change in albumin-to-creatinine ratio in the entire cohort in the multiple linear regression. The albumin-to-creatinine ratiofollow-up-to-albumin-to-creatinine ratiobaseline ratio increased by 8.0% (95% confidence interval, 1.4 to 15.0) per SD increase in change in GFR. When participants with increased GFR (n=343) were compared with those with a reduced GFR (n=903), the ratio increased by 16.3% (95% confidence interval, 1.1 to 33.7). The multivariable adjusted odds ratio for incident albuminuria (n=14) was 4.98 (95% confidence interval, 1.49 to 16.13) for those with an increased GFR (yes/no).

CONCLUSIONS

Increasing GFR is associated with an increase in albumin-to-creatinine ratio and incident albuminuria in the general nondiabetic population. These findings support single-nephron hyperfiltration as a risk factor for albuminuria in the general population.

Chronic kidney disease and high eGFR according to body composition phenotype in adults with normal BMI

BACKGROUND AND AIMS

Body composition contributes to the risk of chronic kidney disease (CKD) and glomerular hyperfiltration. In adults with normal body mass index (BMI), the relationships of body composition with CKD and high estimated glomerular filtration rate (eGFR) are largely unknown.

METHODS AND RESULTS

We analyzed 10,734 adults from the Korean National Health and Nutrition Examination Survey (KNHANES), whose body mass index (BMI) was within the normal range (18.5-24.9 kg/m²). Body composition was categorized into four phenotypes (normal, sarcopenia alone, obesity alone, and sarcopenic obesity) based on appendicular lean mass index (ALMI) and total body fat percentage (TBF%) measured by dual-energy X-ray absorptiometry (DXA). We examined the relationship of CKD and high eGFR (eGFR ≥ 120 ml/min per 1.73 m²) with body composition phenotypes. Sarcopenia alone (14.3%), obesity alone (16.0%), and sarcopenic obesity (10.7%) were prevalent. The association between sarcopenia alone and eGFR was J-shaped, while that between sarcopenic obesity and eGFR was U-shaped. In multivariate logistic regression analysis compared with the normal phenotype, sarcopenic obesity had an elevated odds ratio (OR) for CKD (OR: 1.59, 95% CI: 1.16-2.19). Sarcopenia alone (OR: 1.87; 95% CI: 1.41-2.47) and sarcopenic obesity (OR: 2.37, 95% CI: 1.68-3.36) had elevated OR for high eGFR.

CONCLUSION

These findings suggest that decreased muscle mass and coexistence with excess adiposity show associations with CKD and high eGFR even in adults with normal BMI. Body composition measured by DXA could provide information on the relationship of body composition with CKD and high eGFR.

The Association between Renal Hyperfiltration and the Sources of Habitual Protein Intake and Dietary Acid Load in a General Population with Preserved Renal Function: The KoGES Study

Although the differential response of the kidney to the acute load of various sources of dietary protein in subjects with normal renal function is well known, the influence of habitual dietary protein intake and dietary acid load on renal function has not been tested well. The association between renal hyperfiltration (RHF), the earlier and possibly reversible stage of chronic kidney disease, and the sources of habitual dietary protein and dietary acid load was analyzed with the baseline data of 123,169 middle-aged healthy Koreans of a large prospective cohort study, who had a baseline estimated glomerular filtration rate (eGFR) >60 mL/min/m2 and no known history of diabetes and/or hypertension. eGFR was calculated with the Chronic Kidney Disease Epidemiology Collaboration equation using serum creatinine and RHF was defined as eGFR >95th percentile after adjustment for age, sex, height, and body weight. Dietary acid load was calculated with estimated net endogenous acid production (eNEAP). Although the level of habitual intake of animal protein was positively and vegetable protein was negatively associated with RHF, this association was significant only in women and younger participants (younger than sex-specific median age). The odds for RHF increased as the percentile rank of eNEAP increased until about the 50th percentile and then leveled off. The positive association between eNEAP and RHF was significant in both sexes and age groups. Dietary acid load was associated with RHF regardless of sex and age and rather than the amount of the total or the individual sources of habitual dietary protein, may be a better target for the dietary intervention of chronic kidney disease.

Central obesity associates with renal hyperfiltration in the non-diabetic general population: a cross-sectional study

Background

Obesity is a risk factor for end-stage renal disease. Renal hyperfiltration, defined as an abnormally high glomerular filtration rate (GFR), is a link in the causal chain between diabetes and chronic kidney disease. Whether obesity is associated with hyperfiltration in the non-diabetic general population, remains unresolved due to a lack of consensus regarding the definition of hyperfiltration and the limited precision of high-range GFR estimations with creatinine and/or cystatin C.

Methods

1555 middle-aged participants without diabetes, renal or cardiovascular disease were enrolled from the general population in the Renal Iohexol Clearance Survey from the 6th Tromsø Study (RENIS-T6) between 2007 and 2009. Obesity was assessed using the body mass index (BMI), waist circumference (WC) and the waist-hip ratio (WHR). GFR was measured by iohexol clearance. Dichotomous variables for hyperfiltration were based on two alternative definitions using unadjusted GFR (mL/min) above the 90th percentile. The 90th percentile was age-, sex- and height-specific in one definition and age-, sex-, height- and weight-specific in the other.

Results

In multivariable adjusted logistic regression models, only WHR was consistently associated with hyperfiltration based on both definitions. For the definition based on the age-, sex-, height- and weight-specific 90th percentile, the association with the WHR (odds ratios (95 % confidence intervals)) for hyperfiltration was 1.48 (1.08–2.02) per 0.10 WHR increase.

Conclusions

Central obesity is associated with hyperfiltration in the general population. The WHR may serve as a better indicator of the renal effects of obesity than BMI or WC.

Electronic supplementary material

The online version of this article (doi:10.1186/s12882-016-0386-4) contains supplementary material, which is available to authorized users.

Impact of low-carbohydrate diet on renal function: a meta-analysis of over 1000 individuals from nine randomised controlled trials

We aimed to clarify the effect of low-carbohydrate diet (LCD) on renal function in overweight and obese individuals without chronic kidney disease (CKD). Literature searches were performed using EMBASE, MEDLINE and Cochrane Library until December 2015. We selected articles that reported human studies from their inception until December 2015 in English using the following searching terms: ‘Low carbohydrate diet’ AND (‘Clinical trial’ OR ‘Clinical study’ OR ‘Clinical investigation’ OR ‘Observational study’ OR ‘Cohort study’). We compared the effects of LCD on renal function, defined as change in estimated glomerular filtration rate (eGFR), assessed in randomised-controlled trials. We calculated the mean change in eGFR and the mean change in standard deviations by eGFR or creatinine clearance, and compared the mean change in eGFR and standard deviations in LCD with those in the control diet using fixed-effects models. We selected nine randomised controlled trials including 1687 participants (861 were fed LCD and 826 were fed the control diet). The mean change in eGFR in the LCD group was −4·7 to 24·0 ml/min per 1·73 m2 and that in the control diet group was −4·1 to 10·8 ml/min per 1·73 m2. The mean change in eGFR in the LCD group was greater than that in the control diet (0·13 ml/min per 1·73 m2; 95 % CI 0·00, 0·26). In the present meta-analysis, we identified that the increase in eGFR was greater in LCD compared with the control diet in overweight and obese individuals without CKD.

Clinical predictive factors in diabetic kidney disease progression

Diabetic kidney disease (DKD) represents a major component of the health burden associated with type 1 and type 2 diabetes. Recent advances have produced an explosion of ‘novel’ assay‐based risk markers for DKD, though clinical use remains restricted. Although many patients with progressive DKD follow a classical albuminuria‐based pathway, non‐albuminuric DKD progression is now well recognized. In general, the following clinical and biochemical characteristics have been associated with progressive DKD in both type 1 and type 2 diabetes: increased hemoglobin A1c, systolic blood pressure, albuminuria grade, early glomerular filtration rate decline, duration of diabetes, age (including pubertal onset) and serum uric acid; the presence of concomitant microvascular complications; and positive family history. The same is true in type 2 diabetes for male sex category, in patients following an albuminuric pathway to DKD, and also true for the presence of increased pulse wave velocity. The following baseline clinical characteristics have been proposed as risk factors for DKD progression, but with further research required to assess the nature of any relationship: dyslipidemia (including low‐density lipoprotein, total and high‐density lipoprotein cholesterol); elevated body mass index; smoking status; hyperfiltration; decreases in vitamin D, hemoglobin and uric acid excretion (all known consequences of advanced DKD); and patient test result visit‐to‐visit variability (hemoglobin A1c, blood pressure and high‐density lipoprotein cholesterol). The development of multifactorial ‘renal risk equations’ for type 2 diabetes has the potential to simplify the task of DKD prognostication; however, there are currently none for type 1 diabetes‐specific populations. Significant progress has been made in the prediction of DKD progression using readily available clinical data, though further work is required to elicit the role of several variables, and to consolidate data to facilitate clinical implementation.

Renal Stress Testing in the Assessment of Kidney Disease

As part of human evolutionary development, many human organ systems have innate mechanisms to adapt to increased "work demand" or stress. This reserve capacity can be informative and is used commonly in cardiology to assess cardiac function (e.g., treadmill test). Similarly, the kidney possesses reserve capacity, which can be demonstrated in at least 2 of the following renal domains: glomerular and tubular. When appropriate stimulants are used, healthy patients with intact kidneys can significantly increase their glomerular filtration rate and their tubular secretion. This approach has been used to develop diagnostics for the assessment of renal function. This article reviews both glomerular and tubular kidney stress tests and their respective diagnostic utility.

Renal abnormalities in a cohort of HIV-infected children and adolescents

BACKGROUND

This study aimed to identify the prevalence of renal abnormalities and the evolution of glomerular filtration rate (GFR) among human immunodeficiency virus (HIV)- infected children and adolescents followed up in an infectious disease outpatient pediatric clinic.

METHODS

We performed a cohort study of 115 children and adolescents. Outcomes of two evaluations for urinalysis, microalbuminuria/urinary creatinine ratio, urinary retinol-binding protein (uRBP) concentration, and estimated GFR (eGFR) were obtained for each patient, with an average interval of 6 months between evaluations. These changes were correlated with gender, age, race, body mass index (BMI), height-for-age (H/A) percentile, clinical and immunological classification of HIV infection, use of antiretroviral therapy (ART), HIV viral load (VL), and CD4+ T-lymphocyte count.

RESULTS

Mean patient age at the time of inclusion in the study was 12.6 ± 3.2 years; 50.4 % were male, 81.7 % had acquired immune defeciency syndrome (AIDS), 80.9 % had CD4+ < 500 cells/mm(3), and 87.8 % were on ART. Urinary changes included hematuria (11.3 %), proteinuria (7 %), and microalbuminuria (11.6 %); uRBP was present in 3.8 %; and mean eGFR was 163 ± 32 ml/min/1.73 m(2).

CONCLUSIONS

The subclinical renal abnormalities found in this study may indicate early manifestations of a broad spectrum of renal dysfunction associated with HIV and involves the decision to initiate or modify ART.

Elevated baseline glomerular filtration rate (GFR) is independently associated with a more rapid decline in renal function of patients with type 1 diabetes

AIMS

Renal hyperfiltration is observed prior to the development of diabetic kidney disease (DKD) in patients with type 1 diabetes (T1DM); however its significance remains uncertain. Longitudinal data were used to investigate the association between measured baseline glomerular filtration rate (GFR) and renal function decline in patients with T1DM.

METHODS

This study included 142 adult patients with T1DM and ≥2 measurements of glomerular filtration rate (mGFR; determined by diethylene-triamine-penta-acetic acid plasma clearance). Median follow up was 19 years. Patients were stratified by baseline mGFR quartile. The relationship between baseline mGFR and rate of renal function decline was assessed using random-effect generalized least squares regression, adjusted for age, duration of diabetes, HbA1c, blood pressure, renin-angiotensin-aldosterone system inhibitor therapy, LDL and BMI.

RESULTS

The average rates of decline in renal function for the 2nd (baseline mGFR: 96.4-112.6 ml min-(1) 1.73 m-(2)), 3(rd) (baseline mGFR: 112.6-125.5 ml min- (1) 1.73 m-(2)) and 4th quartiles (baseline mGFR >125.5 ml min-(1) 1.73 m-(2)) were significantly faster than the first quartile (baseline mGFR: 60.9-96.4 ml min-(1) 1.73 m-(2)). In further detail, the average rates of decline in the 2nd (rate of decline 1.25 ml min- (1) 1.73 m-(2) per year, 95% CI: 0.97; 1.52, p=0.008), 3rd (rate of decline 1.35 ml min-(1) 1.73 m-(2) per year, 95% CI: 1.08; 1.62, p= 0.001) and 4th quartiles (rate of decline 1.6 ml min-(1) 1.73 m-(2) per year, 95% CI: 1.34, 1.88, <0.0001) were significantly faster when compared to the first quartile (rate of decline 0.67 ml min-(1) 1.73 m-(2) per year, 95% CI: 0.37; 0.96). Sub-analysis of quartile 4 revealed higher HbA1c measurements throughout follow-up in those with rapid mGFR decline (>3.0 ml min(-1)1.73 m(-2)/year).

CONCLUSIONS

In patients with T1DM, higher baseline mGFR is associate ed with more rapid mGFR decline. Patients with high baseline mGFR who developed rapid mGFR decline had higher HbA1c measurements throughout the study. These findings are consistent with the concept that poor glycaemic control over time may be a determining factor for the rapid renal function decline observed in some hyperfiltering patients.

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.

Prehypertension Tsunami: A Decade Follow-Up of an Iranian Adult Population

OBJECTIVE

Prehypertension is associated with cardiovascular disease (CVD). There is no study to examine the incidence and risk factors of prehypertension in a sex stratified setting. The aim of this study was to examine the effect modification of sex for different risk factors which predicts the progression from normotension to prehypertension in a Middle East population-based cohort, during a median follow-up of 9.2 years.

METHODS

A multivariate Cox analysis was performed among 1466 and 2131 Iranian men and women, respectively, who were free of prehypertension, hypertension, CVD and diabetes at baseline and free of incident hypertension without preceding prehypertension at follow-up. Incident prehypertension at follow-up was defined as systolic blood pressure (SBP) of 120-139 mmHg and/or diastolic blood pressure (DBP) of 80-89 mmHg.

RESULTS

Overall, 1440 new cases of prehypertension were identified resulting in an incidence rate of 593/10000 person-years; the corresponding values for women and men were 489/10000 and 764/10000person-years, respectively. There were significant interactions between gender with age, DBP, waist-to-hip-ratio (WHpR) and estimated glomerular filtration rate (eGFR) (all P-values <0.05) in multivariate analysis. Strong associations were found between age, body mass index (BMI) and SBP with incident prehypertension in both genders. However, the effect of DBP and WHpR was significant among women and 2-hour post challenge plasma glucose (2h-PCPG)was an independent risk factor for men. In the sex-adjusted analysis, glomerular hyperfiltration [Hazard ratio (HR) and 95%CI: 1.01 (1.00-1.01), P-value = 0.02], age, BMI, WHpR, SBP and DBP had higher risks while being female [HR (95%CI): 0.81(0.69-0.94), P-value = 0.01] had a lower risk for incident prehypertension.

CONCLUSION

According to this study results, among Iranian population with high incidence of prehypertension, general adiposity and glomerular hyperfiltration in total, 2h-PCPG in men and central adiposity in women should be emphasized as risk factors for prehypertension.

Can the height-independent Pottel eGFR equation be used as a screening tool for chronic kidney disease in children?

Determination of plasma creatinine (Pcr) should be associated to an estimation of glomerular filtration rate (eGFR). Pottel et al. established a height-independent equation, eGFR = 107.3/(Pcr/Q) where Q is the median of Pcr (Pottel-Belgium). The aims were to 1) determine a local height-independent equation (Pottel-Lyon), 2) evaluate the performance of these equations compared to the Schwartz 2009 and Schwartz-Lyon equations, and 3) evaluate the height-independent equations in laboratory routine. Therefore, 1) all first pediatric Pcr determination (December 2009-June 2011) were collected, and median of Pcr was determined for each 1-year age interval (Q-Lyon), 2) GFR was measured (mGFR) in 359 children (438 measures) and compared to eGFR, and 3) all first Pcr determination (January 2012-June 2013) were used to calculate eGFR with the Pottel-Lyon and the Pottel-Belgium equations. Pcr was determined by an IDMS-standardized enzymatic assay. In the population with a mGFR, the Pottel-Lyon and the Schwartz-Lyon showed the best performance (bias, P10 and P30). However, the performance in identifying patients with a mGFR < 75 mL/min/1.73 m(2) was similar for all the studied equations.

CONCLUSION

The performance of the height-independent and dependent equations to identify mild renal dysfunction is similar. The height-independent Pottel equation could be proposed as an excellent screening tool for kidney disease when height information is not available. "

WHAT IS KNOWN

" • Determination of plasma creatinine in children is rarely associated to an estimation of glomerular filtration rate due to the lack of height information. • Pottel et al. developed a height-independent equation (eGFR = 107.3/(Pcr/Q) where Q is the median of Pcr for each age class. "

WHAT IS NEW

" • The performance of the height-independent (Pottel) or height-dependent (Schwartz) equations is similar to identify renal dysfunction (GFR < 75 mL/min/1.73 m (2) ) in children. • The height-independent Pottel equation could be an excellent screening tool for kidney disease in a general pediatric laboratory when height information is not available.

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.

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.

Association between high-density lipoprotein cholesterol and renal function in elderly hypertension: a cross-sectional study in Chinese population

Few studies have yet investigated the possible association between high-density lipoprotein cholesterol (HDL-C) and kidney function in elderly patients with primary hypertension. Accordingly, the aim of the present study was to evaluate the relationship between HDL-C and kidney function in elderly hypertension. A total of 14,644 elderly hypertensive subjects were enrolled in our cross-sectional study. The patients were categorized based on serum HDL-C level and glomerular filtration rate (GFR) value, respectively. One-way analysis of variance was used to compare the parameters among different groups. Bonferroni correction was performed for multiple comparisons. Analysis of covariance was used to control for confounding factors. The significance of difference between 3 groups and more was determined by chi-square test for categorical variables. Serum creatinine and uric acid were negatively related to HDL-C level, whereas GFR was positively related to HDL-C level in elderly hypertensive patients according to tertiles of HDL-C and tertiles of HDL-C/total cholesterol ratio (all P for trends <0.05). The male elderly hypertensive patients showed stronger relationship between HDL-C and renal function than the female elderly hypertensive subjects. Low HDL-C was associated with renal insufficiency and proteinuria in the hypertensive elderly (P < 0.05). The elderly "renal-hyperfiltrator" appeared to have lower HDL-C level, compared with the "normal renal-filtrator" (P < 0.05). There was an inverse "V" shape between HDL-C and GFR by GFR strata. Our results point out that there is an association of low HDL-C level with impaired kidney function in elderly hypertensive patients. Glomerular hyperfiltration may also affect HDL-C level and sex might be an influential factor for the association of HDL-C with kidney function in elderly hypertension.

A systematic review of glomerular hyperfiltration assessment and definition in the medical literature

BACKGROUND AND OBJECTIVES

Evaluation of glomerular hyperfiltration (GH) is difficult; the variable reported definitions impede comparisons between studies. A clear and universal definition of GH would help in comparing results of trials aimed at reducing GH. This study assessed how GH is measured and defined in the literature.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Three databases (Embase, MEDLINE, CINAHL) were systematically searched using the terms "hyperfiltration" or "glomerular hyperfiltration". All studies reporting a GH threshold or studying the effect of a high GFR in a continuous manner against another outcome of interest were included.

RESULTS

The literature search was performed from November 2012 to February 2013 and updated in August 2014. From 2013 retrieved studies, 405 studies were included. Threshold use to define GH was reported in 55.6% of studies. Of these, 88.4% used a single threshold and 11.6% used numerous thresholds adapted to participant sex or age. In 29.8% of the studies, the choice of a GH threshold was not based on a control group or literature references. After 2004, the use of GH threshold use increased (P<0.001), but the use of a control group to precisely define that GH threshold decreased significantly (P<0.001); the threshold did not differ among pediatric, adult, or mixed-age studies. The GH threshold ranged from 90.7 to 175 ml/min per 1.73 m(2) (median, 135 ml/min per 1.73 m(2)).

CONCLUSION

Thirty percent of studies did not justify the choice of threshold values. The decrease of GFR in the elderly was rarely considered in defining GH. From a methodologic point of view, an age- and sex-matched control group should be used to define a GH threshold.