Predictive performance of renal function equations for patients with chronic kidney disease and normal serum creatinine levels

Age and gender differences in the relationship between hepatitis C infection and all stages of Chronic kidney disease

Chronic kidney disease (CKD) is a worldwide health issue with heavy economic burden. Chronic hepatitis C virus (HCV) infection is a common cause of CKD, which can significantly impact the progression and mortality among patients with CKD. The prevalence of both illnesses is high in Taiwan. A multicentre and population-based cross-sectional study including 24 642 subjects was conducted to explore the association of HCV infection with the prevalence and severity of CKD. The measurements of metabolic parameters, eGFR and CKD stages were compared between subjects with HCV seropositivity and seronegativity. The analyses of association between HCV infection with CKD stages and evaluation of potential risk factors of CKD were performed by gender and age (≤ and >45 years). HCV-seropositive subjects accounted for 6.9% and had a significantly older age. The prevalence of CKD increased in those with HCV seropositivity (16.5%). Significantly higher prevalence of CKD stages ≥3 in HCV-seropositive subjects was noticed (7.8%). Age (>45 year), male gender, alcohol drinking, hypertension, creatinine and HCV infection were the significant factors associated with the presence of CKD. HCV seropositivity was an independent risk factor of developing CKD and associated with an increased risk of having CKD of all stages. The higher prevalence of earlier stage of CKD warrants longitudinal studies with frequent testing on renal function and sufficient duration to determine the changes of eGFR over time. Implementation of effective treatment intervention is also required for these subjects to prevent the progression of CKD to late stages.

Weekly nab-paclitaxel in combination with carboplatin as first-line therapy in patients with advanced non-small-cell lung cancer: analysis of safety and efficacy in patients with renal impairment

INTRODUCTION

Renal impairment in cancer patients can affect treatment tolerability and outcomes. This analysis evaluated the safety and efficacy of nab-paclitaxel (nab-P) versus solvent-based paclitaxel (sb-P), both in combination with carboplatin (C), in patients with advanced non-small-cell lung cancer (NSCLC) and renal impairment.

METHODS

Untreated patients with stage IIIB/IV disease with NSCLC and a performance status of 0/1 were randomly assigned (1:1) to receive 100 mg/m(2)nab-P weekly plus C (under the curve = 6, every 3 weeks) or 200 mg/m(2) sb-P plus C (under the curve = 6) every 3 weeks. The primary end point was overall response rate.

RESULTS

Of 1038 treated patients in the phase III trial, 38% had mild renal impairment (creatinine clearance > 50 to ≤ 80 mL/min; n = 198 for nab-P/C and n = 206 for sb-P/C) and 5% had moderate renal impairment (creatinine clearance ≤ 50 mL/min: n = 26 for nab-P/C and n = 27 for sb-P/C). For nab-P/C versus sb-P/C, the treatment difference in efficacy in patients with either level of renal impairment was comparable to the overall population but did not reach statistical significance, with an overall response rate of 35% versus 27% (response rate ratio, 1.324; P = .060) in patients with mild renal impairment, and 31% versus 19% (response rate ratio, 1.662; P = .300) in patients with moderate renal impairment. Overall survival and progression-free survival were nonsignificantly longer for nab-P/C versus sb-P/C in these subsets. Patients with renal impairment experienced less grade 3 or higher neutropenia and sensory neuropathy, but more thrombocytopenia and anemia with nab-P/C versus sb-P/C.

CONCLUSION

nab-P/C proved beneficial and tolerable in patients with advanced NSCLC and mild and moderate renal impairment.

Competitive interaction between fibroblast growth factor 23 and asymmetric dimethylarginine in patients with CKD

Both fibroblast growth factor 23 (FGF-23) and asymmetric dimethylarginine (ADMA) are associated with progression of CKD. We tested the hypothesis that ADMA and FGF23 are interactive factors for CKD progression in a cohort of 758 patients with CKD in Southern Europe (mean eGFR±SD, 36±13 ml/min per 1.73 m(2)) and in a central European cohort of 173 patients with CKD (MMKD study, mean eGFR, 64±39 ml/min per 1.73 m(2)). In the first cohort, 214 patients had renal events (decrease in eGFR of >30%, dialysis, or kidney transplantation) during a 3-year follow-up. Both intact FGF-23 and ADMA predicted the incidence rate of renal events in unadjusted and adjusted analyses (P<0.001). There was a strong competitive interaction between FGF-23 and ADMA in the risk of renal events (P<0.01 in adjusted analyses); the risk associated with raised ADMA levels was highest in patients with low FGF-23 levels. These results were confirmed in the MMKD cohort, in which FGF-23 level was again an effect modifier of the relationship between plasma ADMA level and renal events (doubling of baseline serum creatinine, dialysis, or kidney transplantation) in the adjusted analyses (P<0.01). Furthermore, in the MMKD cohort there was a parallel, independent competitive interaction between symmetric dimethylarginine level and c-terminal FGF-23 level for the risk for renal events (P=0.001). These findings indicate that the association of ADMA level with the risk of CKD progression is modified by FGF-23 level and provide further evidence that dysregulation of the nitric oxide system is involved in CKD progression.

Estimation of renal function in the intensive care unit: the covert concepts brought to light

Frantic efforts have been made up to this date to derive consensus for estimating renal function in critically ill patients, only to open the Pandora's box. This article tries to explore the various methods available to date, the newer concepts, and the uncared issues that may still prove to be useful in estimating renal function in intensive care unit patients. The concept of augmented renal clearance, which is frequently encountered in critically ill patients, should always be taken into account, as correct therapeutic dosage of drugs sounds vital which in turn depends on correctly calculated glomerular filtration rate. Serum creatinine and creatinine-based formulae have their own demerits that are well known and established. While Cockcroft-Gault and 4-variable modification of diet in renal diseases formulae are highly inadequate in the intensive care setup for estimating glomerular filtration rate, employing isotopic methods is impractical and cumbersome. The 6-variable modification of diet in renal diseases formula fairs better as it takes into account the serum albumin and blood urea nitrogen, too. Jelliffe's and modified Jelliffe's equations take into account the rate of creatinine production and volume of distribution which in turn fluctuates heavily in a critically ill patient. Twenty-four-hour and timed creatinine clearances offer values close to reality although not accurate and cannot provide immediate results. Cystatin C is a novel agent that offers a sure promise as it is least influenced by factors that affect serum creatinine to a major extent. Aminoglycoside clearance, although still in the dark area, may prove a simple yet precise way of estimating glomerular filtration rate in those patients in whom these drugs are therapeutically employed. Optic ratiometric method has emerged as the most sophisticated one in glomerular filtration rate estimation in critically ill patients.

Chronic kidney disease in patients with cancer and its association with occurrence of venous thromboembolism and mortality

INTRODUCTION

The risk for occurrence of venous thromboembolism (VTE) in cancer patients has been the aim of numerous investigations. Chronic kidney disease (CKD) is a frequent comorbidity in cancer patients and has been found to be a risk factor for VTE in the general population. We investigated the association of CKD with VTE and mortality in cancer patients.

METHODS

Patients were recruited into the prospective cohort study, Vienna Cancer and Thrombosis Study (CATS). CKD was estimated with equations for glomerular filtration rate (eGFR) based on serum creatinine by Modification of Diet in Renal Disease (MDRD), CKD Epidemiology collaboration (CKD-EPI) and Cockcroft-Gault equation (C-G). Patients were subsequently classified to stages of CKD according to the Kidney Diseases Outcomes Quality Initiative. Primary endpoint was occurrence of VTE and secondary endpoint was death.

RESULTS

The cohort of 1100 patients was prospectively followed over a median of 723 days. CKD with an eGFR of under 90 ml/min was common with a prevalence of 71.1%, 67.0% or 51.5% of patients calculated with MDRD, CKD-EPI and C-G equations, respectively, but severe CKD (eGFR<30 ml/min) was rare. Patients with a moderately decreased eGFR (90-60 ml/min/1.73 m(2)) based on CKD-EPI had a subdistribution hazard ratio of 0.68 (95% confidence interval 0.43-1.06). An association between CKD and occurrence of VTE or mortality could also not be shown with the other equations.

CONCLUSIONS

In our investigation of a large cohort of cancer patients with a high prevalence of CKD, a reduced eGFR was not an independent risk factor for occurrence of VTE or death.

Ankle-brachial index, toe-brachial index, and cardiovascular mortality in persons with and without diabetes mellitus

BACKGROUND

The prognostic utility of the ankle-brachial index (ABI) may be hampered in persons with diabetes due to peripheral arterial stiffening in the ankles. Stiffening of toe arteries occurs infrequently in diabetes. We aimed to determine the nature of the relationship of the toe-brachial index (TBI) and ABI with cardiovascular disease (CVD) mortality and to determine whether the associations are modified in individuals with diabetes.

METHODS

Individuals with clinically suspected atherosclerotic peripheral arterial disease who underwent ABI and TBI measurements in a vascular laboratory were monitored longitudinally for CVD mortality.

RESULTS

Among 469 participants (89% men), the mean age was 68 ± 9 years, and 36% had diabetes. The mean ABI was 0.83 ± 0.28 and the mean TBI was 0.60 ± 0.24. During median 7.0 years of follow-up, there were 158 CVD deaths. The association of the ABI categories with CVD deaths differed in diabetic vs nondiabetic participants (P = .002 for interaction). In contrast, the association of the TBI categories with CVD deaths was similar, irrespective of diabetes status (P = .17 for interaction). Among diabetic patients, a U-shaped relationship was observed between ABI categories and CVD death: those with low (<0.90) and high (>1.30) ABIs were both at higher risk than those with normal ABIs (range, 0.90-1.30). In nondiabetic patients, association of ABI categories with CVD death was linear, such that those with an ABI >1.30 were at the lowest risk, whereas those with an ABI <0.90 were at higher risk. In contrast, the association of TBI categories with CVD death was linear irrespective of diabetes status. High TBI categories consistently predicted low risk, whereas risk was higher with progressively lower TBI categories.

CONCLUSIONS

Among diabetic individuals with clinically suspected peripheral arterial disease, those with low and high ABIs are both at higher risk of CVD death. In contrast, a linear relationship was observed between TBI categories and CVD death irrespective of diabetes status. These findings suggest that stiffened ankle arteries may limit the predictive value of the ABI in individuals with diabetes, a limitation that may be overcome by measurement of the TBI.

Vitamin D insufficiency is associated with lower physical function in patients with heart failure and diabetes

Vitamin D deficiency is frequent among patients with heart failure (HF) and diabetes, disorders associated with exercise intolerance and muscle weakness. This study aims to search for associations between vitamin D sufficiency and physical function indexes in patients with HF and diabetes. A cross-sectional study of 146 HF patients, 39.7% with diabetes, at a Brazilian tertiary outpatient clinic was performed. Patients underwent clinical evaluation, 6-minute walk test (6 MWT), handgrip strength, physical activity level (IPAQ), and biochemical evaluations including serum 25-hydroxyvitamin D. Classification was done according to vitamin D status (≥ 30 ng/dL, sufficient) and presence/absence of diabetes in vitamin sufficient, no diabetes (DS-C, n = 25), vitamin sufficient, diabetes (DS-DM, n = 18), vitamin deficient, no diabetes (DD-C, n = 63), and vitamin deficient, diabetes (DD-DM, n = 40). Patients age was 55.4 ± 8 yrs; 70.5% had vitamin D deficiency. Clinical characteristics were similar among groups. Total time expended in physical activity was similar among groups (P = 0.26). DS-C covered higher distances in the 6 MWT (392 ± 60 m) versus DD-DM (309 ± 116 m); P = 0.024. Handgrip strength was similar among groups but tended to lower levels in DD-DM (P = 0.074) even after being adjusted to physical activity (P = 0.069). Vitamin D deficiency can influence physical function in HF diabetic patients.

Dyspepsia among patients with chronic kidney disease: a cross sectional study

Backgrounds

Dyspepsia is a condition that affects 25% of the U.S. population, and, when associated with pyrosis, its prevalence reaches 40%. Patients with chronic renal insufficiency not only present higher circulating levels of gastrin and gastric dysmotilty, but also make use of a great amount of drugs for the treatment of their comorbidities. This situation increases the chances of developing gastrointestinal symptoms. The aim of the current study is to evaluate the dyspeptic disease profile in patients undergoing hemodialysis, comparing them with chronic renal disease patients in conservative treatment and non-renal injury patients.

Methods

This is a cross sectional study performed at the Gastroenterology department at Faculdade de Medicina do ABC in São Paulo, Brazil. Three groups were set aside according to the renal function levels calculated using the simplified MDRD formula. They answered three questionnaires that evaluated the presence of dyspepsia, functional dyspepsia and gastroesophageal reflux disease (GERD) associated with the performance of high digestive endoscopy.

Results

A significant difference between the groups was observed concerning the renal function evaluated by the rates of creatinine clearance, creatinine and urea (p < 0.001). The rate of dyspepsia in the control group was higher than in patients with renal function alterations (p = 0.014). There was no difference between groups when it came to the presence of functional dyspepsia and GERD. However, there was a higher use of proton pump inhibitors in the hemodialysis group than in the other groups (p < 0.001).

Conclusion

In the proposed model, there was no positive correlation between the worsening of the renal function and the presence of dyspepsia, functional dyspepsia and GERD. The longitudinal evaluation of hemodialysis patients is hampered by the high mortality rates in this group. There was a higher use of proton pump inhibitors, and it is believed that the dyspeptic symptoms are not acid-related.

Comparison of Cockcroft-Gault and Modification of Diet in Renal Disease Formulas as Predictors of Cardiovascular Outcomes in Patients With Myocardial Infarction Treated With Primary Percutaneous Coronary Intervention

We prospectively assessed the value of estimated glomerular filtration rate (eGFR) by the Modification of Diet in Renal Disease (MDRD) and Cockcroft-Gault (C-G) equations in predicting inhospital adverse outcomes after primary coronary intervention for acute ST-segment elevation myocardial infarction. We classified 647 patients into 3 categories according to eGFR, <60, 60 to 90, and >90 mL/min/1.73 m2. The eGFRC-G classified 17 patients in the >90 mL/min/1.73 m2 subgroup and 6 and 11 patients in the 60 to 90 and <60 mL/min/1.73 m2 subgroups, respectively. In multivariate analysis, patients with eGFRC-G < 60 mL/min/1.73 m2 had 19.5-fold (95% confidence interval [CI] 1.55-178) higher mortality risk and 5.48-fold (95% CI 1.75-24.21) higher major adverse cardiac events risk compared to patients with eGFRC-G >90 mL/min/1.73 m2 ( P = .01 and P = .01, respectively); the eGFRMDRD was not predictive. Although the MDRD equation more accurately estimates GFR in certain populations, the CG formula may be a better predictor of adverse events.

Homoarginine and progression of chronic kidney disease: results from the Mild to Moderate Kidney Disease Study

Background

Homoarginine is an amino acid derivative mainly synthesized in the kidney. It is suggested to increase nitric oxide availability, enhance endothelial function and to protect against cardiovascular diseases. We aimed to investigate the relation between homoarginine, kidney function and progression of chronic kidney disease (CKD).

Methods

We measured plasma homoarginine concentrations in baseline samples of the Mild to Moderate Kidney Disease (MMKD) Study, a prospective cohort study of 227 patients with CKD in Europe. Homoarginine concentrations were available in 182 of the baseline samples and in 139 of the prospectively-followed patients. We correlated homoarginine concentrations to parameters of kidney function. The association between homoarginine and progression of CKD was assessed during a follow-up of up to seven years (median 4.45 years, interquartile range 2.54–5.19) using Cox regression analysis. Progression of CKD was defined as doubling of baseline serum creatinine and/or end-stage renal disease.

Results

Study participants were at baseline on average 47±13 years old and 65% were male. Mean±standard deviation of homoarginine concentrations were 2.5±1.1 µmol/L and concentrations were incrementally lower at lower levels of GFR with mean concentrations of 2.90±1.02 µmol/L (GFR>90 ml/min), 2.64±1.06 µmol/L (GFR 60–90 ml/min), 2.52±1.24 µmol/L (GFR 30–60 ml/min) and 2.05±0.78 µmol/L (GFR<30 ml/min), respectively (p = 0.002). The age- and sex-adjusted risk to reach the renal endpoint was significantly higher by 62% with each decrease by one standard deviation (1.1 µmol/L) of homoarginine (HR 1.62, 95% CI 1.16–2.27, p = 0.005). This association was independent of proteinuria (HR 1.56, 95% CI 1.11–2.20, p = 0.01), and was slightly attenuated when adjusting for GFR (HR 1.40 (95% CI 0.98–1.98, p = 0.06).

Conclusions

Homoarginine concentrations are directly correlated with kidney function and are significantly associated with the progression of CKD. Low homoarginine concentrations might be an early indicator of kidney failure and a potential target for the prevention of disease progression which needs further investigations.

Kinetics of intravenous radiographic contrast medium injections as used on CT: simulation with time delay differential equations in a basic human cardiovascular multicompartment model

OBJECTIVES

To develop a multicompartment model of only essential human body components that predicts the contrast medium concentration vs time curve in a chosen compartment after an intravenous injection. Also to show that the model can be used to time adequately contrast-enhanced CT series.

METHODS

A system of linked time delay instead of ordinary differential equations described the model and was solved with a Matlab program (Matlab v. 6.5; The Mathworks, Inc., Natick, MA). All the injection and physiological parameters were modified to cope with normal or pathological situations. In vivo time-concentration curves from the literature were recalculated to validate the model.

RESULTS

The recalculated contrast medium time-concentration curves and parameters are given. The results of the statistical analysis of the study findings are expressed as the median prediction error and the median absolute prediction error values for both the time delay and ordinary differential equation systems; these are situated well below the generally accepted maximum 20% limit.

CONCLUSION

The presented program correctly predicts the time-concentration curve of an intravenous contrast medium injection and, consequently, allows an individually tailored approach of CT examinations with optimised use of the injected contrast medium volume, as long as time delay instead of ordinary differential equations are used.

ADVANCES IN KNOWLEDGE

The presented program offers good preliminary knowledge of the time-contrast medium concentration curve after any intravenous injection, allowing adequate timing of a CT examination, required by the short scan time of present-day scanners. The injected volume of contrast medium can be tailored to the individual patient with no more contrast medium than is strictly needed.

SLC22A2 is associated with tubular creatinine secretion and bias of estimated GFR in renal transplantation

Genome-wide association studies reported SLC22A2 variants to be associated with serum creatinine. As SLC22A2 encodes the organic cation transporter 2 (OCT2), the association might be due to an effect on tubular creatinine handling. To test this hypothesis we studied the association of SLC22A2 polymorphisms with phenotypes of net tubular creatinine secretion: fractional creatinine excretion (FEcreat) and bias of estimated glomerular filtration rate (eGFR). We also studied the association with end-stage renal disease (ESRD) and graft failure (GF) in renal transplant recipients. SLC22A2 single nucleotide polymorphisms (SNPs), rs3127573 and rs316009, were genotyped in 1,142 ESRD patients receiving renal transplantation and 1,186 kidney donors as controls. GFR was measured with (125)I-iothalamate clearance. Creatinine clearance was also assessed. FEcreat was calculated from the simultaneous clearances of creatinine and (125)I-iothalamate. Donor rs316009 was associated with FEcreat (beta -0.053, P = 0.024) and with estimated [modification of diet in renal disease (MDRD) and Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI)] but not measured GFR. In line with this, donor rs316009 was associated with bias of the MDRD and CKD-EPI but not the Cockroft-Gault equation. Both SNPs were associated with ESRD: odds ratios [95% CI] 1.39 [1.16-1.67], P = 0.00065, and 1.23 [1.02-1.48], P = 0.042, for rs3127573 and rs316009, respectively. Neither SNP was associated with GF. Thus, SLC22A2 is associated with phenotypes of net tubular creatinine secretion and ESRD.

Unrecognized renal insufficiency and chemotherapy-associated adverse effects among breast cancer patients

Several studies have shown that more than half of cancer patients have unrecognized renal insufficiency (RI), which is a reduced glomerular filtration rate (GFR) with normal serum creatinine. The aim of this study was to determine whether unrecognized RI is associated with an increased risk for chemotherapy-associated adverse effects in breast cancer patients treated with combined doxorubicin and cyclophosphamide treatment. GFR was estimated for 95 breast cancer patients from January 2005 to August 2009 using the Cockcroft-Gault formula. Unrecognized RI was defined as GFR less than 75 ml/min/1.73 m and the patients were grouped according to their estimated GFR. Logistic regression models were used to assess the effect of GFR on clinical outcomes. In total, 49 (52%) patients experienced at least one of the following chemotherapy-associated adverse effects during the course of treatment: an episode of neutropenic fever with hospital admission, a delay in chemotherapy treatment for a medical reason, a need for dose adjustment because of toxicity of the chemotherapeutic drugs, and the need for use of granulocyte colony-stimulating factor. The incidence of these adverse effects occurred more frequently in patients with GFR less than 75 compared with patients with GFR at least 75 (64 vs. 42%, odds ratio 5.29, 95% confidence interval 2.10-13.33) and remained statistically significant after adjustment for age, BMI, and initial doses of chemotherapeutic drugs (odds ratio 3.56, 95% confidence interval 1.08-11.67). Neutropenic fever, dose delay, and dose adjustment as separate outcomes occurred more frequently in the GFR less than 75 group but lost statistical significance after adjustment. Our results demonstrate that unrecognized RI is associated with an increased risk for chemotherapy-associated adverse events in this patient population. Further prospective studies are required to determine whether a dose reduction in patients with unrecognized RI reduces adverse effects without adversely affecting the benefit of treatment.

Assessment of adult formulas for glomerular filtration rate estimation in children

BACKGROUND

Estimated glomerular filtration rate (eGFR) is an important diagnostic instrument in clinical practice. The National Kidney Foundation-Kidney Disease Quality Initiative (NKF-KDOQI) guidelines do not recommend using formulas developed for adults to estimate GFR in children; however, studies confirming these recommendations are scarce. The aim of our study was to evaluate the accuracy of the new Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) formula, the Modification of Diet in Renal Disease (MDRD) formula, and the Cockcroft-Gault formula in children with various stages of chronic kidney disease (CKD).

METHODS

A total of 550 inulin clearance (iGFR) measurements for 391 children were analyzed. The cohort was divided into three groups: group 1, with iGFR >90 ml/min/1.73 m(2); group 2, with iGFR between 60 and 90 ml/min/1.73 m(2); group 3, with iGFR of <60 ml/min/1.73 m(2).

RESULTS

All formulas overestimate iGFR with a significant bias (p < 0.001), present poor accuracies, and have poor Spearman correlations. For an accuracy of 10 %, only 11, 6, and 27 % of the eGFRs are accurate when using the MDRD, CKD-EPI, and Cockcroft-Gault formulas, respectively. For an accuracy of 30 %, these formulas do not reach the NKF-KDOQI guidelines for validation, with only 25, 20, and 70 % of the eGFRs, respectively, being accurate.

CONCLUSIONS

Based on our results, the performances of all of these formulas are unreliable for eGFR in children across all CKD stages and cannot therefore be applied in the pediatric population group.

CKD-EPI instead of MDRD for candidates to kidney donation

BACKGROUND

The determination of the glomerular filtration rate (GFR) is critical for the selection of a potential kidney donor. The complex and impractical techniques for the measurement of GFR have led to the development of equations to estimate GFR. Modification of diet in renal disease (MDRD) formula is the most widely used but its performance is poor because it systematically underestimates GFR above 60 mL/min. A new formula called the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) seems to overcome this limitation but needs to be tested in healthy potential kidney donors.

METHODS

From 2007 to 2011, a cross-sectional study was performed on 85 adults who were candidates for living-related kidney donation. GFR was measured by nonradiolabeled iothalamate clearance determined by high-performance liquid chromatography, and renal function was estimated by using CKD-EPI and MDRD equations. The overall performance of the equations was analyzed, and the estimation for GFR above 90 mL/min was studied by means of receiver operating characteristic curves.

RESULTS

The mean (SD) (range) of the measured GFR was 116 (24) (64-160) mL/min per 1.73 m(2), estimated GFR with CKD-EPI was 108 (22) (64-153) mL/min per 1.73 m(2), and MDRD was 99 (28) (46-157) mL/min per 1.73 m(2). CKD-EPI presented lower bias (3.3 vs. 10.2 mL/min/1.73 m(2)), higher precision [interquartile range (minimum value-maximum value), 25 (53-140) vs. 32 (43-161) ml/min] and higher accuracy (100% vs. 89%) compared with MDRD.

CONCLUSION

The CKD-EPI equation showed a higher performance than the MDRD equation in the GFR estimation of healthy population. CKD-EPI is applicable instead of MDRD, to subjects or candidates for kidney donation to avoid wrong GFR underestimates, which may lead to an inappropriate exclusion of candidates.

Race adjustment for estimating glomerular filtration rate is not always necessary

Background

Estimated glomerular filtration rate (eGFR) is very important in clinical practice, although it is not adequately tested in different populations. We aimed at establishing the best eGFR formulas for a Brazilian population with emphasis on the need for race correction.

Methods

We evaluated 202 individuals with chronic kidney disease (CKD) and 42 without previously known renal lesions that were additionally screened by urinalysis. Serum creatinine and plasma clearance of iohexol were measured in all cases. GFR was estimated by the Mayo Clinic, abbreviated Modification of Diet in Renal Disease (MDRD) and Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) formulas, and creatinine clearance was estimated by the Cockcroft-Gault (CG) formula. Plasma clearance of iohexol was used as the gold standard for GFR determination and for the development of a Brazilian formula (BreGFR).

Results

Measured and estimated GFR were compared in 244 individuals, 57% female, with a mean age of 41 years (range 18–82). Estimates of intraclass correlation coefficients among the plasma clearance of iohexol and eGFR formulas were all significant (p < 0.001) and corresponded to the following scores: CG 0.730; obesity-adjusted CG 0.789; Mayo Clinic 0.804; MDRD 0.848; MDRD1 (without race adjustment) 0.846; CKD-EPI 0.869; CKD-EPI1 (without race adjustment) 0.876, and BreGFR 0.844.

Conclusions

All cited eGFR formulas showed a good correlation with the plasma clearance of iohexol in the healthy and diseased conditions. The formulas that best detected reduced eGFR were the BreGFR, CKD-EPI, and CKD-EPI1 formulas. Notably, the race correction included in the MDRD and CKD-EPI formulas was not necessary for this population, as it did not contribute to more accurate results.

Comparison of glomerular filtration rate estimated by plasma clearance method with modification of diet in renal disease prediction equation and Gates method

Glomerular filtration rate (GFR) prediction equations are widely used in clinical practice for quick assessment of kidney function. Gates method using radionuclide technique is an alternative to prediction equations for quick assessment of GFR. Aim of the study was to compare Gates method and modification of diet in renal disease (MDRD) equation in a sizeable patient population with wide range of renal function to evaluate their clinical utility. GFR was estimated in 897 subjects with wide range of renal function by gates method, and MDRD equation and results were compared against measured GFR. Subjects were divided in to 4 groups (0-30 ml, 31-60 ml, 61-90 ml, >90 ml) on the basis of measured GFR and comparison between two methods done through linear regression analysis. Analysis of R² indicated that 56% of the interindividual variability for Gates GFR was in accordance to variation in measured GFR, in the GFR range of (0-30 ml), this value dropped to 39% in the GFR range of 31-60 ml, 40% in the GFR range of 61-90 ml, 26.4% in the GFR range of >90 ml, the corresponding figure for MDRD GFR were 47.9%, 31.1%, 17.6% and 16.1%, respectively. Gates method is more precise for GFR estimation at all levels of renal function.

Cardio-renal syndrome: new perspective in diagnostics

Chronic heart failure and chronic renal failure are at epidemic proportions. These patients have significantly altered cardiac, renal, and all-cause outcomes. Much of the current research has focused on treating these individual organs in isolation. Although there are positive data on outcomes with neurohormonal modulation, they, however, remain underused. At present, data lacks for novel treatment options, while evidence continues to point at significantly worsened prognosis. Current diagnostic tools that detect acute changes in renal function or renal injury appear retrospective, which often hinder meaningful diagnostic and therapeutic decisions. This review is aimed at exploring the importance of accurate assessment of renal function for the heart failure patient by providing a synopsis on cardio-renal physiology and establishing the possibility of novel approaches in bridging the divide.

Predictive performance of eGFR equations in South Africans of African and Indian ancestry compared with ⁹⁹mTc-DTPA imaging

BACKGROUND

South African guidelines for early detection and management of chronic kidney disease (CKD) recommend using the Cockcroft-Gault (CG) or Modification of Diet in Renal Disease (MDRD) equations for calculating estimated glomerular filtration rate (eGFR) with the correction factor, 1.212, included for MDRD-eGFR in black patients. We compared eGFR against technetium-99m-diethylenetriaminepentaacetic acid ((99m)Tc-DTPA) imaging.

METHODS

Using clinical records, we retrospectively recorded demographic, clinical, and laboratory data as well as (99m)Tc-DTPA-measured GFR (mGFR) results obtained from routine visits. Data from 148 patients of African (n = 91) and Indian (n = 57) ancestry were analyzed.

RESULTS

Median (IQR) mGFR was 38.5 (44) ml/min/1.73 m(2), with no statistical difference between African and Indian patients (P = 0. 573). In African patients with stage 3 CKD, MDRD-eGFR (unadjusted for black ethnicity) overestimated mGFR by 5.3% [2.0 (16.0) ml/min/1.73 m(2)] compared to CG-eGFR and MDRD-eGFR (corrected for black ethnicity) that overestimated mGFR by 17.7% [6.0 (15.0) ml/min/1.73 m(2)] and 17.1% [6.0 (17.5) ml/min/1.73 m(2)], respectively. In stage 1-2, CKD eGFR overestimated mGFR by 52.5, 38.0, and 19.3% for CG, MDRD (ethnicity-corrected), and MDRD (without correction), respectively. In Indian stage 3 CKD patients, MDRD-eGFR underestimated mGFR by 35.6% [-21.0 (6.5) ml/min/1.73 m(2)] and CG-eGFR by 4.4% [-2.0 (27.0) ml/min/1.73 m(2)], while in stage 1-2 CKD, CG-eGFR and MDRD-eGFR overestimated mGFR by 13.8 and 6.3%, respectively.

CONCLUSION

MDRD-eGFR calculated without the African-American correction factor improved GFR prediction in African CKD patients and using the MDRD correction factor of 1.0 in Indian patients as in Caucasians may be inappropriate.

Renal dysfunction in patients with heart failure with preserved versus reduced ejection fraction: impact of the new Chronic Kidney Disease-Epidemiology Collaboration Group formula

BACKGROUND

Prior studies in heart failure (HF) have used the Modification of Diet in Renal Disease (MDRD) equation to calculate estimated glomerular filtration rate (eGFR). The Chronic Kidney Disease-Epidemiology Collaboration Group (CKD-EPI) equation provides a more-accurate eGFR than the MDRD when compared against the radionuclide gold standard. The prevalence and prognostic import of renal dysfunction in HF if the CKD-EPI equation is used rather than the MDRD is uncertain.

METHODS AND RESULTS

We used individual patient data from 25 prospective studies to stratify patients with HF by eGFR using the CKD-EPI and the MDRD equations and examined survival across eGFR strata. In 20 754 patients (15 962 with HF with reduced ejection fraction [HF-REF] and 4792 with HF with preserved ejection fraction [HF-PEF]; mean age, 68 years; deaths per 1000 patient-years, 151; 95% CI, 146-155), 10 589 (51%) and 11 422 (55%) had an eGFR <60 mL/min using the MDRD and CKD-EPI equations, respectively. Use of the CKD-EPI equation resulted in 3760 (18%) patients being reclassified into different eGFR risk strata; 3089 (82%) were placed in a lower eGFR category and exhibited higher all-cause mortality rates (net reclassification improvement with CKD-EPI, 3.7%; 95% CI, 1.5%-5.9%). Reduced eGFR was a stronger predictor of all-cause mortality in HF-REF than in HF-PEF.

CONCLUSIONS

Use of the CKD-EPI rather than the MDRD equation to calculate eGFR leads to higher estimates of renal dysfunction in HF and a more-accurate categorization of mortality risk. Renal function is more closely related to outcomes in HF-REF than in HF-PEF.

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.

Novel therapeutic agents for the management of patients with multiple myeloma and renal impairment

Renal impairment is a major complication of multiple myeloma. Patients presenting with severe renal impairment represent a greater therapeutic challenge and generally have poorer outcome. However, once patients with renal impairment achieve remission, their outcomes are comparable with those of patients without renal impairment. Therapies that offer substantial activity in this setting are needed. Bortezomib, thalidomide, and lenalidomide have substantially improved the survival of patients with multiple myeloma. Here we review the pharmacokinetics, activity, and safety of these agents in patients with renal impairment. Bortezomib can be administered at the full approved dose and schedule in renally impaired patients; similarly, no dose reductions are required with thalidomide. The pharmacokinetics of lenalidomide is affected by its renal route of excretion, and dose adjustments are recommended for moderate/severe impairment. Substantial evidence has emerged showing that these novel agents improve outcomes of patients with renal impairment, including impairment reversal. Bortezomib, thalidomide, and lenalidomide (at the recommended doses) are active options for patients with mild to moderate impairment, although limited data are available for thalidomide. Information on lenalidomide-based combinations is still emerging, but the available data indicate considerable activity. Substantial evidence indicates that bortezomib-high-dose dexamethasone with or without a third drug (e.g., cyclophosphamide, thalidomide, or doxorubicin) is an appropriate option for patients with any degree of renal impairment.

Clinical features and outcomes in patients with diabetes mellitus undergoing coronary artery bypass graft in a reference center in southern Brazil

OBJECTIVE

To describe clinical/laboratory features of patients undergoing coronary artery bypass graft (CABG) in a cardiology reference center.

METHODS

Cohort study; data from patients undergoing CABG (January 2004 to February 2006, n = 717) were evaluated for clinical/laboratory features before, during and after surgery (infections, duration of hospital stay, deaths).

RESULTS

Patients were 61.9 ± 11 years old, 67.1% males, 29.6% diabetics. Intraoperatively, diabetics had a central venous catheter placed for a longer period (p < 0.001), but extracorporeal circulation, aortic clamping and total surgery times were similar to those for non-diabetics. Infection occurred in 19.1% of patients (40.1% diabetics vs. 10.3% non-diabetics, p < 0.001). The duration of hospital stay was longer for patients with diabetes vs. non-diabetic patients, but there was no difference in deaths between the two groups (p = 0.797).

CONCLUSION

Patients with diabetes undergoing CABG develop more infectious diseases and stay longer in hospital than non-diabetics.

Longitudinal evaluation of FGF23 changes and mineral metabolism abnormalities in a mouse model of chronic kidney disease

Fibroblast growth factor 23 (FGF23) is a phosphaturic and vitamin D-regulatory hormone of putative bone origin that is elevated in patients with chronic kidney disease (CKD). The mechanisms responsible for elevations of FGF23 and its role in the pathogenesis of chronic kidney disease-mineral bone disorder (CKD-MBD) remain uncertain. We investigated the association between FGF23 serum levels and kidney disease progression, as well as the phenotypic features of CKD-MBD in a Col4a3 null mouse model of human autosomal-recessive Alport syndrome. These mice exhibited progressive renal failure, declining 1,25(OH)(2)D levels, increments in parathyroid hormone (PTH) and FGF23, late-onset hypocalcemia and hyperphosphatemia, high-turnover bone disease, and increased mortality. Serum levels of FGF23 increased in the earliest stages of renal damage, before elevations in blood urea nitrogen (BUN) and creatinine. FGF23 gene transcription in bone, however, did not increase until late-stage kidney disease, when serum FGF23 levels were exponentially elevated. Further evaluation of bone revealed trabecular osteocytes to be the primary cell source for FGF23 production in late-stage disease. Changes in FGF23 mirrored the rise in serum PTH and the decline in circulating 1,25(OH)(2)D. The rise in PTH and FGF23 in Col4a3 null mice coincided with an increase in the urinary fractional excretion of phosphorus and a progressive decline in sodium-phosphate cotransporter gene expression in the kidney. Our findings suggest elevations of FGF23 in CKD to be an early marker of renal injury that increases before BUN and serum creatinine. An increased production of FGF23 by bone may not be responsible for early increments in FGF23 in CKD but does appear to contribute to FGF23 levels in late-stage disease. Elevations in FGF23 and PTH coincide with an increase in urinary phosphate excretion that likely prevents the early onset of hyperphosphatemia in the face of increased bone turnover and a progressive decline in functional renal mass.

Which method of estimating renal function is the best predictor of mortality after coronary artery bypass grafting?

OBJECTIVES

Definitions of renal function in patients undergoing coronary artery bypass graft surgery (CABG) vary in the literature. We sought to investigate which method of estimating renal function is the best predictor of mortality after CABG.

METHODS

We analysed the preoperative and postoperative renal function data from all patients undergoing isolated CABG from January 1998 through December 2007. Preoperative and postoperative renal function was estimated using serum creatinine (SeCr) levels, creatinine clearance (CrCl) determined by the Cockcroft-Gault formula and the glomerular filtration rate (e-GFR) estimated by the Modification of Diet in Renal Disease (MDRD) formula. Receiver operator characteristic (ROC) curves and area under the ROC curves were calculated.

RESULTS

In 9987 patients, CrCl had the best discriminatory power to predict early as well as late mortality, followed by e-GFR and finally SeCr. The odds ratios for preoperative parameters for early mortality were closer to 1 than those of the postoperative parameters.

CONCLUSIONS

Renal function determined by the Cockcroft-Gault formula is the best predictor of early and late mortality after CABG. The relationship between renal function and mortality is non-linear. Renal function as a variable in risk scoring systems such as the EuroSCORE needs to be reconsidered.

Nephrotoxicity of HAART

Highly active antiretroviral therapy (HAART) and other medical therapies for HIV-related infections have been associated with toxicities. Antiretroviral therapy can contribute to renal dysfunction directly by inducing acute tubular necrosis, acute interstitial nephritis, crystal nephropathy, and renal tubular disorders or indirectly via drug interactions. With the increase in HAART use, clinicians must screen patients for the development of kidney disease especially if the regimen employed increases risk of kidney injury. It is also important that patients with chronic kidney disease (CKD) are not denied the best combinations, especially since most drugs can be adjusted based on the estimated GFR. Early detection of risk factors, systematic screening for chronic causes of CKD, and appropriate referrals for kidney disease management should be advocated for improved patient care. The interaction between immunosuppressive therapy and HAART in patients with kidney transplants and the recent endorsement of tenofovir/emtricitabine by the Centers for Disease Control (CDC) for preexposure prophylaxis bring a new dimension for nephrotoxicity vigilance. This paper summarizes the common antiretroviral drugs associated with nephrotoxicity with particular emphasis on tenofovir and protease inhibitors, their risk factors, and management as well as prevention strategies.

A comparison of cystatin C- and creatinine-based prediction equations for the estimation of glomerular filtration rate in black South Africans

BACKGROUND

Serum creatinine (S-Cr)-based prediction equations are commonly used for estimating glomerular filtration rate (GFR). However, S-Cr concentration is also affected by other factors such as tubular secretion, muscle mass, diet, gender and age. Serum cystatin C (S-Cys C)-based prediction equations have been proposed as an improved potential alternative as S-Cys C levels are not influenced by many of the factors that affect creatinine concentration other than GFR. This may be of great benefit to patients with low muscle mass such as those infected with human immunodeficiency virus who are at increased risk for the development of renal impairment. The aim of this study was to develop and evaluate a S-Cys C-based prediction equation for different stages of renal disease in black South Africans.

METHODS

One hundred patients with varying degrees of renal function were enrolled in the study. The plasma clearance of (51)Cr-EDTA, a gold standard method, was used to measure GFR (mGFR). In addition, serum was analysed for S-Cr and S-Cys C on each participant. This dataset was split into a development dataset (n = 50) and a test dataset (n = 50). The development dataset was used to formulate a S-Cys C- and S-Cr-based prediction equation using multiple linear regression analysis. These equations together with the four-variable MDRD and CKD-EPI equation were then tested on the test dataset.

RESULTS

In the test dataset, accuracy within 15% of measured GFR was 68% for the S-Cys C equation and 48% for the S-Cr equation. Root mean square error for S-Cr eGFR was 10.7 mL/min/1.73 m(2) for those patients with mGFR < 60 mL/min/1.73 m(2) and 25.5 mL/min/1.73 m(2) for those patients with mGFR > 60 mL/min/1.73 m(2). Root mean square error for S-Cys C eGFR was 10.2 mL/min/1.73 m(2) for those patients with mGFR < 60 mL/min/1.73 m(2) and 11.9 mL/min/1.73 m(2) for those patients with mGFR > 60 mL/min/1.73 m(2).

CONCLUSIONS

In this study, S-Cys C-based prediction equations appear to be more precise than those of S-Cr for those patients with mGFR > 60 mL/min/1.73 m(2) and may therefore be of benefit in the earlier detection of renal impairment.

Higher body mass index is associated with higher fractional creatinine excretion in healthy subjects

BACKGROUND

Accurate glomerular filtration rate (GFR) measurement in normal to high range is important for epidemiological studies and workup for kidney donation. Creatinine-based equations perform poorly in this GFR range. Creatinine clearance (CrCl) provides a substitute, provided urine is collected accurately and tubular creatinine handling can be accounted for. The latter is poorly characterized in the normal GFR range.

METHODS

Therefore, we studied performance of CrCl, fractional creatinine excretion (FE(creat)) and its determinants in 226 potential kidney donors (47% males, mean 53 ± 10 years). GFR was assessed as (125)I-iothalamate clearance, simultaneously with 2-h CrCl and 24-h CrCl.

RESULTS

Mean GFR was 101 ± 18, 2-h CrCl 110 ± 20 and 24-h CrCl 106 ± 29 mL/min/1.73 m(2). Mean bias of 24 h CrCl was 7.4 [inter-quartile range -6.7 to 20.0] mL/min/1.73 m(2), precision (R(2)) 0.39 and 30% accuracy 82%. Mean FE(creat) was 110 ± 11%. FE(creat) correlated with body mass index (BMI) (r = 0.34, P < 0.001). Consequently, bias of 24-h CrCl increased from 2.7 (inter-quartile range -6.5 to 16.7) to 8.6 (inter-quartile range -5.8 to 20.5) and 12.6 (inter-quartile range 7.0 to 25.4) mL/min in subjects with BMI <25, 25-30 and >30 kg/m(2), respectively (P < 0.05). On multivariate analysis, BMI and gender were predictors of FE(creat).

CONCLUSIONS

CrCl systematically overestimates GFR in healthy subjects. The overestimation significantly correlates with BMI, with higher FE(creat) in subjects with higher BMI. The impact of BMI on tubular creatinine secretion can be accounted for, when using CrCl for GFR assessment in the normal to high range, by the following formula: GFR = 24-h CrCl - (22.75 + 0.76 × BMI - 0.29 × mean arterial pressure (-6.11 if female).

Renal function equations before and after living kidney donation: a within-individual comparison of performance at different levels of renal function

BACKGROUND AND OBJECTIVES

The Modification of Diet in Renal Disease (MDRD) study equation and the Cockcroft-Gault (CG) equation perform poorly in the (near-) normal range of GFR. Whether this is due to the level of GFR as such or to differences in individual characteristics between healthy individuals and patient with chronic kidney disease (CKD) is unknown.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We evaluated the performance of MDRD, CG per BSA (CG/(BSA)) and Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations compared with measured GFR (mGFR; I-iothalamate) at 4 months before and 2 months after donation in 253 consecutive living kidney donors.

RESULTS

mGFR declined from 103 ± 15 to 66 ± 11 ml/min per 1.73 m(2) after donation. All equations underestimated mGFR at both time points. Arithmetic performance analysis showed improved performance after donation of all equations, with significant reduction of bias after donation. Expressed as percentage difference, mGFR-estimated GFR (eGFR) bias was reduced after donation only for CG/(BSA). Finally, in 295 unselected individuals who were screened for donation, mGFR was below the cutoff for donation of 80 ml/min per 1.73 m(2) in 19 individual but in 166, 98, and 74 for MDRD, CDK-EPI, and CG/(BSA), respectively.

CONCLUSIONS

A higher level of GFR as such is associated with larger absolute underestimation of true GFR by eGFR. For donor screening purposes, eGFR should be interpreted with great caution; when in doubt, true GFR should be performed to prevent unjustified decline of prospective kidney donors.

Chronic kidney disease in kidney transplant recipients-is it different from chronic native kidney disease?

BACKGROUND

The rate of change in estimated glomerular filtration rate (ΔeGFR), factors influencing ΔeGFR, and its association with mortality has not been well studied in renal transplant recipients. METHODS.: Adult kidney-only recipients between January 2001 and December 2004, with surviving grafts 1 year after transplantation, from England and Wales were followed up till 31 December 2006, graft failure or death. The four variable modification of diet in renal disease equation was used to estimate GFR and ΔeGFR assessed using linear least square regression. ΔeGFR of -1 mL/min/1.73m per year and above was considered to be stable or improving function. Linear regression and Cox regression analyses were used to examine factors influencing ΔeGFR and its association with mortality, respectively.

RESULTS

Of the 2, 927 patients included, ΔeGFR was -1.3±6.0 mL/min/1.73 m per year and eGFR remained stable or improved in the majority (54.8%). Baseline graft function at 1 year or live donor status did not influence ΔeGFR. Male donor to female recipient transplantation, younger recipients, diabetes, white race, and human leukocyte antigen mismatch were associated with faster decline in eGFR. ΔeGFR was not associated with mortality when censored for graft failure.

CONCLUSIONS

Majority of renal transplant recipients experienced stable or improved graft function. Specific donor and recipient characteristics influenced the rate of decline in eGFR. The lack of association of ΔeGFR with mortality, the stability of eGFR in the majority, and influence of donor characteristics on ΔeGFR suggest caution when applying prognosis knowledge from the native kidney disease to the kidney transplant population.

Accurate, fast, and convenient measurement of glomerular filtration rate in potential renal transplant donors

BACKGROUND

Measurement of glomerular filtration rate (GFR) is essential in the risk evaluation of potential kidney donors. The optimal method of measuring GFR involves using clearance techniques. However, clearance techniques are technically complex and time consuming. The goal of this study is to evaluate a different method of measuring GFR, one that retains the accuracy of a clearance technique and adds the convenience of a plasma creatinine measurement.

METHODS

Fifty subjects, including both normal and patients with different degrees of renal dysfunction, were included in the initial validation study. GFR was measured simultaneously using a continuous infusion of I-iothalamate and external radioactivity measurement after a single intravenous injection of Tc-labeled diethylenetriaminepentaacetic acid (Tc-DTPA). After validation, the renal function of 80 potential renal transplant donors was measured using only external radiation detection.

RESULTS

External radioactivity decreases versus time with first-order kinetics. The rate of clearance of Tc-DTPA was measured as the slope (kappa) of the natural logarithm of external radioactivity corrected for radioactive decay versus time. There was an excellent correlation between kappa and simultaneous GFR measurements done with I-iothalamate. Nonlinear regression analysis of kappa GFR values obtained in potential renal transplant donors versus frequencies indicates a mean value and variance similar to normal reported values obtained with clearance techniques. Estimated GFR and 24-hr plasma creatinine clearance underestimate GFR with greater variance.

CONCLUSIONS

Measurements of external whole tissue radioactivity after intravenous injection of Tc-DTPA represents an accurate, fast, and convenient way to measure total and individual kidney GFR, addressing an important concern during the risk evaluation of potential renal transplant donors.

A comparison of cystatin C- and creatinine-based prediction equations for the estimation of glomerular filtration rate in black South Africans

BACKGROUND

Serum creatinine (S-Cr)-based prediction equations are commonly used for estimating glomerular filtration rate (GFR). However, S-Cr concentration is also affected by other factors such as tubular secretion, muscle mass, diet, gender and age. Serum cystatin C (S-Cys C)-based prediction equations have been proposed as an improved potential alternative as S-Cys C levels are not influenced by many of the factors that affect creatinine concentration other than GFR. This may be of great benefit to patients with low muscle mass such as those infected with human immunodeficiency virus who are at increased risk for the development of renal impairment. The aim of this study was to develop and evaluate a S-Cys C-based prediction equation for different stages of renal disease in black South Africans.

METHODS

One hundred patients with varying degrees of renal function were enrolled in the study. The plasma clearance of (51)Cr-EDTA, a gold standard method, was used to measure GFR (mGFR). In addition, serum was analysed for S-Cr and S-Cys C on each participant. This dataset was split into a development dataset (n = 50) and a test dataset (n = 50). The development dataset was used to formulate a S-Cys C- and S-Cr-based prediction equation using multiple linear regression analysis. These equations together with the four-variable MDRD and CKD-EPI equation were then tested on the test dataset.

RESULTS

In the test dataset, accuracy within 15% of measured GFR was 68% for the S-Cys C equation and 48% for the S-Cr equation. Root mean square error for S-Cr eGFR was 10.7 mL/min/1.73 m(2) for those patients with mGFR < 60 mL/min/1.73 m(2) and 25.5 mL/min/1.73 m(2) for those patients with mGFR > 60 mL/min/1.73 m(2). Root mean square error for S-Cys C eGFR was 10.2 mL/min/1.73 m(2) for those patients with mGFR < 60 mL/min/1.73 m(2) and 11.9 mL/min/1.73 m(2) for those patients with mGFR > 60 mL/min/1.73 m(2).

CONCLUSIONS

In this study, S-Cys C-based prediction equations appear to be more precise than those of S-Cr for those patients with mGFR > 60 mL/min/1.73 m(2) and may therefore be of benefit in the earlier detection of renal impairment.

Underestimation of impaired kidney function with serum creatinine

Serum creatinine (SCr) levels are frequently used as a screening test to assess impaired renal function; however, patients can have significantly decreased glomerular filtration rate (GFR) with normal SCr values and making the recognition of kidney dysfunction more difficult. Hence, this study was designed to determine the extent of misclassification of the patients who have significantly reduced GFR as calculated by reexpressed four variable modification of diet in renal disease (MDRD) equation but, normal range of SCr. The study included 1040 in and out patients referred by physicians for serum creatinine measurement. When an exclusion criterion was applied 928 patients were qualified for the study. SCr was measured in 928 patients by a Roche kinetic compensated Jaffe's assay. GFR was calculated using reexpressed four variable MDRD study equation. Of the 928 patients 270 (29.1%) had renal dysfunction on the basis of eGFR (<60 ml/min/1.73 m(2)). However, with SCr only 162 (17.5%) patients had abnormal renal function (>1.5 mg/dl) and SCr values misrepresented (108) 11.6% patients with impaired kidney function. In addition, more females, about 15% were failed to detect by SCr method in contrast to males of 9%. This study documented that, a large proportion of patients with impaired renal function are not diagnosed if clinicians rely solely on normal SCr as evidence of normal renal function. Inclusion of eGFR calculated by re-expressed 4 variable MDRD equation may facilitates the early identification and intervention of patients with renal impairment.