Kidney function estimating equations: where do we stand?

Evaluation of limited sampling methods for estimation of tacrolimus exposure in adult kidney transplant recipients

AIMS

To examine the predictive performance of limited sampling methods for estimation of tacrolimus exposure in adult kidney transplant recipients.

METHODS

Twenty full tacrolimus area under the concentration-time curve from 0 to 12 h post-dose (AUC(0-12)) profiles (AUCf) were collected from 20 subjects. Predicted tacrolimus AUC(0-12) (AUCp) was calculated using the following: (i) 42 multiple regression-derived limited sampling strategies (LSSs); (ii) five population pharmacokinetic (PK) models in the Bayesian forecasting program TCIWorks; and (iii) a Web-based consultancy service. Correlations (r(2)) between C(0) and AUCf and between AUCp and AUCf were examined. Median percentage prediction error (MPPE) and median absolute percentage prediction error (MAPE) were calculated.

RESULTS

Correlation between C(0) and AUCf was 0.53. Using the 42 LSS equations, correlation between AUCp and AUCf ranged from 0.54 to 0.99. The MPPE and MAPE were <15% for 29 of 42 equations (62%), including five of eight equations based on sampling taken ≤2 h post-dose. Using the PK models in TCIWorks, AUCp derived from only C(0) values showed poor correlation with AUCf (r(2)=0.27-0.54) and unacceptable imprecision (MAPE 17.5-31.6%). In most cases, correlation, bias and imprecision estimates progressively improved with inclusion of a greater number of concentration time points. When concentration measurements at 0, 1, 2 and 4 h post-dose were applied, correlation between AUCp and AUCf ranged from 0.75 to 0.93, and MPPE and MAPE were <15% for all models examined. Using the Web-based consultancy service, correlation between AUCp and AUCf was 0.74, and MPPE and MAPE were 6.6 and 9.6%, respectively.

CONCLUSIONS

Limited sampling methods better predict tacrolimus exposure compared with C(0) measurement. Several LSSs based on sampling taken 2 h or less post-dose predicted exposure with acceptable bias and imprecision. Generally, Bayesian forecasting methods required inclusion of a concentration measurement from >2 h post-dose to adequately predict exposure.

Can partial nephrectomy preserve renal function and modify survival in comparison with radical nephrectomy?

OBJECTIVE

To investigate whether radical nephrectomy (RN) and nephron-sparing surgery (NSS) for T1 renal cell carcinoma influence renal function, oncological outcome or survival rate.

MATERIAL AND METHODS

A retrospective study was performed, including 290 nephrectomies for tumours of a diameter of less than 7 cm; 174 radical nephrectomies were compared to 116 nephron-sparing surgeries. Preoperative and pathological data were compared between the two groups. The glomerular filtration rate was estimated using the abbreviated Modification of Diet and Renal Disease (MDRD4) study equation. The evolution of renal function was analysed from 6 months to 4 years after surgery, and the oncological outcomes were evaluated by means of cancer and non-cancer survival curves.

RESULTS

The results showed a major impairment in renal function in the RN group compared to those who underwent NSS (25 vs 7 ml/min/1.73 m², 6 months after surgery), a difference that was maintained over time. Moreover, patients undergoing RN had a greater chance of developing renal failure. Overall, the survival curves showed a higher mortality rate for the RN group (p = 0.034), although the cancer-specific mortality rate did not show any statistically significant differences (p = 0.079).

CONCLUSIONS

For stage T1 renal cortical tumours, NSS should, whenever possible, be regarded as the primary therapeutic option, given that it obtains similar oncological outcomes to RN and preserves renal function, which seems to translate into a lower overall mortality rate.

Use of sirolimus in liver transplant recipients with renal insufficiency: a systematic review and meta-analysis

Sirolimus is used in patients with renal insufficiency after liver transplantation (LT) and especially in those with calcineurin inhibitor (CNI)-associated nephrotoxicity. We conducted a systematic review of all randomized controlled trials and observational studies to test the hypothesis that the use of sirolimus is associated with an improvement in renal function at 1 year in LT recipients with renal insufficiency [glomerular filtration rate (GFR) < 60 mL/minute or creatinine level ≥ 1.5 mg/dL]. We performed a search of all major databases, conference proceedings, and relevant journals through December 2009 and contacted content experts, corresponding authors, and the pharmaceutical manufacturer. A random effects model was used to determine the pooled estimate of the change in renal function and pooled risk estimates of adverse events that may be associated with sirolimus-based therapy at 1 year. Eleven studies (three randomized controlled trials and eight observational studies) met the final inclusion criteria. A nonsignificant improvement of 3.38 mL/minute [95% confidence interval (CI) = -2.93 to 9.69] was observed in methodologically sound observational studies and controlled trials reporting the primary outcome. In controlled trials, baseline GFR >50 mL/min sirolimus use was associated with an improvement of 10.35 mL/minute (95% CI = 3.98-16.77) in GFR or creatinine clearance. Sirolimus was not significantly associated with death [relative risk (RR) = 1.12, 95% CI = 0.66-1.88] or graft failure (RR = 0.80, 95% CI = 0.45-1.41), although reporting was incomplete. It was associated with a statistically significant risk of infection (RR = 2.47, 95% CI = 1.14-5.36), rash (RR = 7.57, 95% CI = 1.75-32.70), ulcers (RR = 7.44, 95% CI = 2.03-27.28), and discontinuation of therapy (RR = 3.61, 95% CI = 1.32-9.89).

CONCLUSION

Conversion to sirolimus from CNIs is associated with a nonsignificant improvement in renal function in LT recipients with renal insufficiency, although the results are limited by heterogeneity, a risk of bias, and a lack of standardized reporting.

Advances in glomerular filtration rate-estimating equations

PURPOSE OF REVIEW

Estimated glomerular filtration rate (eGFR) is now commonly reported by clinical laboratories. Here, we review the performance of current creatinine and cystatin C-based estimating equations as well as demonstration of their utility in public health and clinical practice.

RECENT FINDINGS

Lower levels of GFR are associated with multiple adverse outcomes, including acute kidney injury and medical errors. The new Chronic Kidney Disease-Epidemiology Collaboration (CKD-EPI) equation improves performance and risk prediction compared with the Modification of Diet in Renal Disease study equation. Current cystatin C-based equations are not accurate in all populations, even in those with reduced muscle mass or chronic illness, in which cystatin C would be expected to outperform creatinine. eGFR reporting has led to a greater number of referrals to nephrologists, but the increased numbers do not appear to be excessive or burdensome. The Modification of Diet in Renal Disease study equation appears to be able to provide drug dosage adjustments similar to the Cockcroft-Gault equation.

SUMMARY

Estimated GFRs and their reporting can improve and facilitate clinical practice for chronic kidney disease. Understanding strengths and limitations facilitates their optimal use. Endogenous filtration markers, alone or in combination, which are less dependent on non-GFR determinants of the filtration markers, are necessary to lead to more accurate eGFRs.

Daclizumab induction therapy in liver transplant recipients with renal insufficiency

BACKGROUND

The role of interleukin 2 (IL-2) receptor antibodies to avoid the nephrotoxic effects of calcineurin inhibitors in the early post-liver transplant (LT) period is not well defined.

AIM

To examine the use of daclizumab induction in LT recipients with renal insufficiency.

METHODS

Between 2002 and 2005, 62 patients (median pre-LT creatinine 2.4 mg/dL, IQR 1.9-3.7) received daclizumab induction with tacrolimus being administered when serum creatinine was <2.0 mg/dL. A concurrent comparison group (n = 221, 2002-2005) received tacrolimus-based immunosuppression without daclizumab (median pre-LT creatinine 1.1 mg/dL, IQR 0.9-1.4). A second historical comparison group (n = 103, 1995-2005) not receiving daclizumab was matched to the daclizumab patients by pre-LT serum creatinine (2.2 mg/dL, IQR 1.8-3.1). All patients received mycophenolate mofetil and steroids.

RESULTS

Serum creatinine improved in the daclizumab group (-1.0 mg/dL, IQR -2.2 to -0.4) and worsened in the concurrent comparison group (+0.2 mg/dL, IQR 0-0.5) from pre-LT to 4 months. However, there was no difference when daclizumab group was compared with the historical comparison group matched on pre-LT creatinine (median change: -0.8 mg/dL vs. -0.7 mg/dL). Daclizumab induction was not associated with improvement in renal function at 4 months (P = 0.34) after adjusting for pre-LT creatinine, age, gender, hepatitis C status and simultaneous liver kidney transplantation.

CONCLUSION

The incremental benefit offered by induction therapy with IL-2 receptor antibodies to preserve renal function is questionable.

Quality-improvement strategies for the management of hypertension in chronic kidney disease in primary care: a systematic review

BACKGROUND

Chronic kidney disease (CKD) is a relatively recently recognised condition. People with CKD are much more likely to suffer from cardiovascular events than progress to established renal failure. Controlling systolic blood pressure should slow the progression of disease and reduce mortality and morbidity. However, no systematic review has been conducted to explore the effectiveness of quality-improvement interventions to lower blood pressure in people with CKD.

AIM

To assess the effectiveness of quality-improvement interventions to reduce systolic blood pressure in people with CKD in primary care, in order to reduce cardiovascular risk and slow the progression of renal disease.

METHOD

Papers were identified from the trial data bases of the Cochrane Effective Practice and Organisation of Care Group (EPOC) and Cochrane renal groups. In a three-round process, at least two investigators read the papers independently. Studies were initially excluded based on their abstracts, if these were not relevant to primary care. Next, full papers were read, and again excluded on relevance. Quantitative and, where this was not possible, qualitative analyses of the findings were performed.

RESULTS

The selected studies were usually carried out on high-risk populations including ethnic minorities. The interventions were most often led by nurses or pharmacists. Three randomised trials showed a combined effect of a reduction in systolic blood pressure of 10.50 mmHg (95% confidence interval [CI] = 5.34 to 18.41 mmHg). One non-randomised study showed a reduction in systolic blood pressure of 9.30 mmHg (95% CI = 3.01 to 15.58 mmHg).

CONCLUSION

Quality-improvement interventions can be effective in lowing blood pressure, and potentially in reducing cardiovascular risk and slowing progression in CKD. Trials are needed in low-risk populations to see if the same improvements can be achieved.

Lack of association between hepatitis C infection and chronic kidney disease

BACKGROUND & AIMS

Chronic kidney disease (CKD) can have a negative impact on the natural history of hepatitis C virus infection (HCV) infection; patients with HCV and CKD often have adverse outcomes. We evaluated a large and geographically diverse group of patients to determine whether HCV status has an independent effect on the risk of developing CKD.

METHODS

We conducted a cohort study of 167,569 patients included in a national health care claims database from January 1, 2003-December 31, 2006, with a mean follow-up of 25.3 months. We used multivariable logistic regression analyses to measure the independent effect of HCV status on the baseline prevalence of and progression to CKD (estimated glomerular filtration rate, <60 mL/min/1.73 m(2)).

RESULTS

The baseline prevalence of CKD was similar in patients with versus those without HCV (5.3% vs 5.1%, P = .3). Similarly, among patients with preserved renal function at baseline (n = 82,629), there was no difference in the overall progression to CKD in patients with versus those without HCV (3.8% vs 3.5%, P = .1). HCV status was not associated with progression to CKD, even after adjusting for patient demographics, comorbidities, and use of relevant medications (odds ratio, 0.92; 95% confidence interval, 0.79-1.08).

CONCLUSIONS

We found no association between HCV and risk of development of CKD. These data are relevant in counseling HCV patients regarding the impact of HCV on renal function.

Screening for chronic kidney disease in HIV-infected patients

With improved survival afforded by highly active antiretroviral therapy (HAART), CKD has emerged as one of the primary comorbid conditions affecting HIV-infected individuals. Although CKD in HIV-infected individuals is classically thought of as a consequence of advanced HIV infection such as in the case of HIV-associated nephropathy, several factors likely contribute to the development CKD in HIV infection. These factors include genetic predisposition, age-related decline in kidney function, HAART-related metabolic changes, exposure to multiple nephrotoxic medications, and concurrent conditions such as hepatitis C or illicit drug use. Similar to the general population, proteinuria and impaired kidney function are associated with faster progression to acquired immune deficiency syndrome and death. Given the prevalence and impact of kidney disease on the course of HIV infection and its management, current guidelines recommend screening all HIV-infected individuals for kidney disease. This review focuses on the current guidelines for kidney disease screening and discusses traditional as well as promising strategies for detecting CKD in this vulnerable population.

Development and validation of GFR-estimating equations using diabetes, transplant and weight

BACKGROUND

We have reported a new equation (CKD-EPI equation) that reduces bias and improves accuracy for GFR estimation compared to the MDRD study equation while using the same four basic predictor variables: creatinine, age, sex and race. Here, we describe the development and validation of this equation as well as other equations that incorporate diabetes, transplant and weight as additional predictor variables.

METHODS

Linear regression was used to relate log-measured GFR (mGFR) to sex, race, diabetes, transplant, weight, various transformations of creatinine and age with and without interactions. Equations were developed in a pooled database of 10 studies [2/3 (N = 5504) for development and 1/3 (N = 2750) for internal validation], and final model selection occurred in 16 additional studies [external validation (N = 3896)].

RESULTS

The mean mGFR was 68, 67 and 68 ml/min/ 1.73 m(2) in the development, internal validation and external validation datasets, respectively. In external validation, an equation that included a linear age term and spline terms in creatinine to account for a reduction in the magnitude of the slope at low serum creatinine values exhibited the best performance (bias = 2.5, RMSE = 0.250) among models using the four basic predictor variables. Addition of terms for diabetes and transplant did not improve performance. Equations with weight showed a small improvement in the subgroup with BMI <20 kg/m(2).

CONCLUSIONS

The CKD-EPI equation, based on creatinine, age, sex and race, has been validated and is more accurate than the MDRD study equation. The addition of weight, diabetes and transplant does not significantly improve equation performance.

Comparison of drug dosing recommendations based on measured GFR and kidney function estimating equations

BACKGROUND

Kidney disease alters the pharmacokinetic disposition of many medications, requiring dosage adjustment to maintain therapeutic serum concentrations. The Cockcroft-Gault (CG) equation is used for pharmacokinetic studies and drug dosage adjustments, but the Modification of Diet in Renal Disease (MDRD) Study equation is more accurate and more often reported by clinical laboratories than the CG equation.

STUDY DESIGN

Diagnostic test study.

SETTINGS & PARTICIPANTS

Pooled data set for 5,504 participants from 6 research studies and 4 clinical populations with measured glomerular filtration rate (GFR).

INDEX TEST

Estimated kidney function using the MDRD Study and CG equations incorporating actual (CG) or ideal body weight (CG(IBW)) and standardized serum creatinine concentrations.

REFERENCE TEST

Measured GFR assessed by using iodine-125-iothalamate urinary clearance.

OUTCOME

Concordance of assigned kidney function categories designated by the Food and Drug Administration (FDA) Guidance for Industry for pharmacokinetic studies and recommended dosages of 15 medications cleared by the kidneys.

RESULTS

Concordance of kidney function estimates with measured GFR for FDA-assigned kidney function categories was 78% for the MDRD Study equation compared with 73% for the CG equation (P < 0.001) and 66% for the CG(IBW) equation (P < 0.001). Concordance between the MDRD Study equation and CG and CG(IBW) equations was 78% and 75%, respectively (P < 0.001). Concordance of kidney function estimates with measured GFR for recommended drug dosages was 88% for MDRD Study equation compared with 85% for the CG equation (P < 0.001) and 82% for the CG(IBW) equation (P < 0.001), with lower concordance when dosing recommendations for drugs included narrow GFR ranges. Concordance rates between the CG and CG(IBW) equations and MDRD Study equation were 89% and 88%, respectively (P < 0.05).

LIMITATIONS

Results based on simulation rather than pharmacokinetic studies. Outcome was drug dosage recommendations, rather than observed drug efficacy and safety.

CONCLUSIONS

The MDRD Study equation can also be used for pharmacokinetic studies and drug dosage adjustments. As more accurate GFR-estimating equations are developed, they should be used for these purposes.

Comparison of drug dosing recommendations based on measured GFR and kidney function estimating equations

BACKGROUND

Kidney disease alters the pharmacokinetic disposition of many medications, requiring dosage adjustment to maintain therapeutic serum concentrations. The Cockcroft-Gault (CG) equation is used for pharmacokinetic studies and drug dosage adjustments, but the Modification of Diet in Renal Disease (MDRD) Study equation is more accurate and more often reported by clinical laboratories than the CG equation.

STUDY DESIGN

Diagnostic test study.

SETTINGS & PARTICIPANTS

Pooled data set for 5,504 participants from 6 research studies and 4 clinical populations with measured glomerular filtration rate (GFR).

INDEX TEST

Estimated kidney function using the MDRD Study and CG equations incorporating actual (CG) or ideal body weight (CG(IBW)) and standardized serum creatinine concentrations.

REFERENCE TEST

Measured GFR assessed by using iodine-125-iothalamate urinary clearance.

OUTCOME

Concordance of assigned kidney function categories designated by the Food and Drug Administration (FDA) Guidance for Industry for pharmacokinetic studies and recommended dosages of 15 medications cleared by the kidneys.

RESULTS

Concordance of kidney function estimates with measured GFR for FDA-assigned kidney function categories was 78% for the MDRD Study equation compared with 73% for the CG equation (P < 0.001) and 66% for the CG(IBW) equation (P < 0.001). Concordance between the MDRD Study equation and CG and CG(IBW) equations was 78% and 75%, respectively (P < 0.001). Concordance of kidney function estimates with measured GFR for recommended drug dosages was 88% for MDRD Study equation compared with 85% for the CG equation (P < 0.001) and 82% for the CG(IBW) equation (P < 0.001), with lower concordance when dosing recommendations for drugs included narrow GFR ranges. Concordance rates between the CG and CG(IBW) equations and MDRD Study equation were 89% and 88%, respectively (P < 0.05).

LIMITATIONS

Results based on simulation rather than pharmacokinetic studies. Outcome was drug dosage recommendations, rather than observed drug efficacy and safety.

CONCLUSIONS

The MDRD Study equation can also be used for pharmacokinetic studies and drug dosage adjustments. As more accurate GFR-estimating equations are developed, they should be used for these purposes.

Prevalence of anemia in elderly patients in primary care: impact on 5-year mortality risk and differences between men and women

BACKGROUND

Increased mortality in patients with anemia has been demonstrated in disabled, seriously ill or hospitalized patients. In industrialized nations with their aging societies, however, elderly but apparently healthy family-physician patients are an important demographic group from a public-health perspective. We therefore set out to evaluate the prevalence of anemia in this group and associations between anemia and 5-year all-cause mortality, adjusted for multiple other established risk factors and chronic diseases.

METHODS

This was a monitored, prospective cohort study in Germany with 344 representative family physicians who documented, consecutively, elderly patients (aged >or= 65 years). Extensive fasting plasma parameters were collected at baseline. Anemia at inclusion was defined according to World Health Organization criteria (hemoglobin below 12 g/dl in women and 13 g/dl in men). All participants were followed up for death of any cause for 5.3 years.

RESULTS

Among the 6880 individuals, 2905 men and 3975 women, aged 65-95 (mean age 72.5), mild anemia (hemoglobin levels >or=10 g/dl) was found in 6.1% of women and 8.1% of men. Among those patients, 36.1% of anemic men and 15.0% of anemic women died. In a Cox proportional hazards analysis, multiple adjusted for potential confounders including major comorbidities, a near doubling of the 5-year mortality risk in anemic men (hazard ratio [HR] 1.9; 95% confidence interval [CI] 1.5-2.4) was found, while in anemic women there was no risk increase at all (HR 1.1; 95% CI 0.8-1.6). Even if patients with the lowest hemoglobin concentration (<11 g/dl for women, <12 g/dl for men) are singled out for multiple-adjusted analysis, anemia in men was related to a significant mortality risk (HR 3.3; 95% CI 2.1-5.1), but not in women (HR 1.85; 95% CI 0.97-3.53).

CONCLUSION

In typical elderly patients without severe comorbidities, mild anemia was significantly associated with greater mortality in men but not in women. Given the impact of sex on outcomes of older subjects with mild anemia, the current definition of anemia should be adjusted for elderly males towards a higher hemoglobin threshold. Interventional trials will be needed to determine whether a consistent correction of anemia improves mortality of older men.

Magnetic resonance nephrourographic techniques and applications: how we do it

Chronic kidney disease is a significant public health problem, and a comprehensive evaluation of renal disease often requires accurate evaluation of both kidney structure and function. Magnetic resonance (MR) nephrourography refers to newly developed imaging techniques that have the ability to provide a quantitative assessment of renal function, especially glomerular filtration rate and renal blood flow. Our review outlines several different methodologies that are present in the literature and also details the specifics of our own methods for renal imaging. Though varied, all MR imaging methods use the common steps of image acquisition, image postprocessing, and tracer kinetics modeling of the processed image data. The optimal methodology should be practical and based primarily on simplicity, speed, and reproducibility. The combination of anatomic and quantitative functional information of the kidneys provided by MR imaging allows for a safe, comprehensive evaluation of renal disease, with particular utility in the settings of urinary tract obstruction and renal transplantation.

Performance evaluation of a particle-enhanced turbidimetric cystatin C assay on the Abbott ci8200 analyzer

OBJECTIVES

Glomerular filtration rate (GFR) is widely accepted as the best overall measure of kidney function. Cystatin C is a novel endogenous GFR marker that has been shown to be superior to creatinine for estimation of GFR in several studies. There is a need for cystatin C assays adapted to routine chemistry instrument to minimize turnaround times and allowing 24 h/day availability.

MATERIALS AND METHODS

We have evaluated a new cystatin C assay developed for Architect cSystem (Abbott Laboratories, Abbott Park, IL, USA).

RESULTS

The cystatin C assay showed good agreement with the corresponding assay from Dade Behring (Deerfield, IL, USA). The assay has a very low total imprecision and a good linearity.

CONCLUSIONS

The new cystatin C assay is an interesting alternative to current cystatin C assays. On an Architect cSystem the assay can be performed with the same turnaround times and availability as creatinine.

A prospective, double-blind, randomized, controlled trial on the efficacy and cardiorenal safety of iodixanol vs. iopromide in patients with chronic kidney disease undergoing coronary angiography with or without percutaneous coronary intervention

OBJECTIVES

This study was undertaken to compare the renal safety as well as cardiovascular (CV) effects and diagnostic image quality of iso-osmolar iodixanol vs. low-osmolar iopromide in patients with chronic kidney disease (CKD) undergoing coronary interventions.

BACKGROUND

With the growing number of contrast-enhanced procedures being performed for coronary artery disease management, the safety and efficacy of iodinated contrast media (CM) have come under increased scrutiny.

METHODS

: Patients with CKD (CrCl < or =60 mL/min) were randomized to iodixanol (n = 106) or iopromide (n = 102). The primary endpoint was incidence of contrast-induced nephropathy (CIN), defined as an increase in serum creatinine (SCr) > or =25% or 0.5 mg/dL within 72 hr of CM administration. Secondary endpoints were mean SCr increase, a composite of CV events in-hospital and 30 days postdischarge, and diagnostic image quality.

RESULTS

: CIN incidence was significantly lower with iodixanol than iopromide (5.7% vs. 16.7%; P = 0.011). Baseline SCr (OR 2.21, 95% CI: 1.25-3.47; P = 0.031), iopromide use (OR 2.56, 95% CI: 1.18-5.76; P = 0.024), and CM volume (OR 2.01, 95% CI: 1.01-3.21; P = 0.038) were identified as independent risk factors for CIN. Cardiovascular events were reduced with iodixanol (1.9% vs. 8.8%; P = 0.025); diagnostic image quality was similar for both CM (P = 0.353).

CONCLUSIONS

: Consistent with several previous trials comparing iso-osmolar iodixanol and low-osmolar comparator CM, iodixanol was associated with a lower incidence of CIN and fewer CV events than iopromide.

Elevated uric acid increases the risk for kidney disease

Recent epidemiologic studies suggest that uric acid predicts the development of new-onset kidney disease, but it is unclear whether uric acid is an independent risk factor. In this study, data from 21,475 healthy volunteers who were followed prospectively for a median of 7 yr were analyzed to examine the association between uric acid level and incident kidney disease (estimated GFR [eGFR] <60 ml/min per 1.73 m(2)). After adjustment for baseline eGFR, a slightly elevated uric acid level (7.0 to 8.9 mg/dl) was associated with a nearly doubled risk for incident kidney disease (odds ratio 1.74; 95% confidence interval 1.45 to 2.09), and an elevated uric acid (> or =9.0 mg/dl) was associated with a tripled risk (odds ratio 3.12; 95% confidence interval 2.29 to 4.25). These increases in risk remained significant even after adjustment for baseline eGFR, gender, age, antihypertensive drugs, and components of the metabolic syndrome (waist circumference, HDL cholesterol, blood glucose, triglycerides, and BP). In a fully adjusted spline model, the risk for incident kidney disease increased roughly linearly with uric acid level to a level of approximately 6 to 7 mg/dl in women and 7 to 8 mg/dl in men; above these levels, the associated risk increased rapidly. In conclusion, elevated levels of uric acid independently increase the risk for new-onset kidney disease.

Reliability of GFR formulas based on serum creatinine, with special reference to the MDRD Study equation

Estimation of glomerular filtration rate (GFR) is central to the diagnosis, evaluation and management of chronic kidney disease (CKD). This review summarizes data on the performance of equations using serum creatinine to estimate GFR, particularly the Modification of Diet in Renal Disease (MDRD) Study equation. The size of studies evaluating GFR estimation equations and their level of sophistication in estimating bias, precision, validity and sensitivity to the source population have improved over the past decade. We update our review from 2006, which included 7 studies with over 500 individuals and 12 studies with 50-499 individuals with measured GFR evaluating the MDRD Study and Cockcroft-Gault equations. More recent studies include an individual level pooling analysis of 5504 participants in 10 studies which showed that creatinine calibration to reference methods improved the performance of the MDRD Study equation but increased bias for the Cockcroft-Gault equation. The MDRD Study equation had a bias of 3.0 %, interquartile range of 29.0 % and percentage of estimates within 30 % of the measured GFR value (P(30)) of 82 % for estimates below 60 mL/(min x 1.73 m(2)). Above this value, the bias was greater (8.7 %) and estimates are less useful since 30 % error is a large absolute error in GFR. Results vary across studies but are generally similar with disappointing performance in the high GFR range, which is of particular interest in early diabetic nephropathy. New equations using serum creatinine can reduce the bias present in the high GFR range but are unlikely to dramatically improve precision, suggesting a need for additional markers. Finally, algorithms are needed to tailor clinical practice based on data from GFR estimates and other participant characteristics, including the source population and level of proteinuria.

How accurate is dynamic contrast-enhanced MRI in the assessment of renal glomerular filtration rate? A critical appraisal

PURPOSE

To evaluate the current literature to see if the published results of MRI-glomerular filtration rate (GFR) stand up to the claim that MRI-GFR may be used in clinical practice. Claims in the current literature that Gadolinium (Gd) DTPA dynamic contrast enhanced (DCE) MRI clearance provides a reliable estimate of glomerular filtration are an overoptimistic interpretation of the results obtained. Before calculating absolute GFR from Gd-enhanced MRI, numerous variables must be considered.

MATERIALS AND METHODS

We examine the methodology in the published studies on absolute quantification of MRI-GFR. The techniques evaluated included the dose and volume of Gd-DTPA used, the speed of injection, acquisition sequences, orientation of the subject, re-processing, conversion of signal to concentration and the model used for analysis of the data as well as the MRI platform.

RESULTS

Claims in the current literature that using DCE MRI "Gd DTPA clearance provides a good estimate of glomerular filtration" are not supported by the data presented and a more accurate conclusion should be that "no MRI approach used provides a wholly satisfactory measure of renal GFR function."

CONCLUSION

This study suggests that DCE MRI-GFR results are not yet able to be used as a routine clinical or research tool. The published literature does not show what change in DCE MRI-GFR is clinically significant, nor do the results in the literature allow a single DCE MRI-GFR measurement to be correlated directly with a multiple blood sampling technique.

Estimation of glomerular filtration rate in South Asian healthy adult kidney donors

AIM

We evaluated the performance of serum creatinine based equations to estimate glomerular filtration rate (GFR) in South Asian healthy renal donors.

METHODS

GFR by 99mTc-diethylenetriamine pentaacetic acid (DTPA) renogram (mGFR) in 599 renal donors was measured. GFR was estimated using a six variable modification of diet in renal disease formula (MDRD1), a four variable MDRD formula (MDRD2), Cockcroft-Gault creatinine clearance (CG CrCl), Cockcroft-Gault glomerular filtration rate (CG GFR) and the Mayo Clinic formula (Mayo GFR). The performance of various prediction equations was compared for global bias, precision (R(2)) and accuracy (percentage of estimated GFR (eGFR) falling within 15% and 30% of mGFR).

RESULTS

The mean age was 37.4 +/- 11 years and 48.2% were male. The mGFR was 95.5 +/- 11.6 mL/min per 1.73 m(2). The bias (mL/min per 1.73 m(2)) was 7.5 +/- 0.9, -9.0 +/- 0.75, 13.1 +/- 0.9, 7.5 +/- 0.9 and 23.4 +/- 0.76 for CG CrCl, CG GFR, MDRD1, MDRD2 and Mayo GFR, respectively. R(2) was 0.082 for CG CrCl and MDRD1, 0.081 for CG GFR and MDRD2 and 0.045 for Mayo GFR. The percentages of eGFR falling within 15% and 30% of mGFR were 50.5 and 80.1 for CG CrCl, 65.8 and 84 for CG GFR, 50 and 74 for MDRD1, 54.3 and 80.1 for MDRD2 and 32 and 63.4 for Mayo GFR. Overall CG GFR performed better in estimating GFR in all subjects.

CONCLUSION

The CG GFR equation was better than other equations to estimate GFR in South Asian healthy renal donors. We propose a new equation derived from the regression model in our study population to estimate GFR in a South Asian healthy adult population.

Prevalence of chronic kidney disease in population-based studies: systematic review

BACKGROUND

Chronic kidney disease (CKD) is becoming a major public health problem worldwide. This article reviews the published evidence of prevalence of CKD in population-based study samples that used the standardized definition from the Kidney Disease Outcomes Quality Initiative of the National Kidney Foundation (K/DOQI) practice guideline, and particularly focus on performance of serum-creatinine based equations for GFR estimation. We provide a summary of available data about the burden of CKD in various populations.

METHODS

We performed a systematic review of available published data in MEDLINE. A combination of various keywords relevant to CKD was used in this research. Related data of included studies were extracted in a systematic way.

RESULTS

A total of 26 studies were included in this review. The studies were conducted in different populations, and the number of study participants ranged from 237 to 65181. The median prevalence of CKD was 7.2% in persons aged 30 years or older. In persons aged 64 years or older prevalence of CKD varied from 23.4% to 35.8%. Importantly, the prevalence of CKD strongly depended on which estimating equations were used. The Modification of Diet in Renal Disease Study (MDRD) equation was likely to be preferred in recent epidemiological studies compared to the adjusted Cockcroft-Gault (CG) equation.

CONCLUSION

Worldwide, CKD is becoming a common disease in the general population. Accurately detecting CKD in special groups remains inadequate, particularly among elderly persons, females or other ethnic groups such as Asians.

Variability in creatinine excretion in adult diabetic, overweight men and women: consequences on creatinine-based classification of renal disease

BACKGROUND

It is crucial to estimate renal function in diabetic patients. However, formulas are inadequate in this population whereas creatinine clearance (C(cr)) on a 24-h urine collection may be valuable only if we can improve its reproducibility.

OBJECTIVE

To evaluate in diabetic patients whether standardised procedures of 24-h urine collection improve the day-to-day variability in creatinine urinary excretion and the subsequent precision of the measured C(cr).

METHODS

The C(cr) from two consecutive 24-h urine collections was measured in 201 consecutive diabetic inpatients. Procedures of 24-h urine collection were standardised, and implementation was supervised at a diabetes clinic.

RESULTS

Pearson's correlation coefficients of the two 24-h creatinine urinary excretion were significant (r(2)=0.64 in women and r(2)=0.65 in men, p<0.0001) but the daily variability in creatinine urinary excretion was high (14.9% in women and 17.4% in men). As a consequence, the agreement between the two consecutive measurements of C(cr) was poor. First, Bland-Altman plots showed large 95% limits of agreement (-34.3 to 34.6 mL/min/1.73 m(2) in women and -39.0 to 52.0 mL/min/1.73 m(2) in men). Secondly, there was a poor agreement for classifying patients according to the National Kidney Foundation classification >90, 60-89.9, 30-59.9, and <30 mL/min/1.73 m(2) (Kappa coefficients=0.61, 0.42, 0.65, and 0.74, respectively).

CONCLUSIONS

Despite standardised procedures of 24-h urine collection, day-to-day variability in creatinine urinary excretion in adult diabetic men and women remains important, and may lead to misclassification of renal disease.

Monitoring renal function and limitations of renal function tests

Chronic kidney disease (CKD) is a world-wide public health problem, with adverse outcomes of kidney failure, cardiovascular disease, and premature death. The National Kidney Foundation, through its Kidney Disease Quality Outcome Initiative (K/DOQI) and other National institutions, recommend glomerular filtration rate (GFR) estimates for the definition, classification, screening, and monitoring of CKD. Prediction equations based on serum creatinine values were chosen both for adults (Cockcroft-Gault [C-G] and Modification of Diet in Renal Disease [MDRD] study equations) and for children (Schwartz and Counahan-Barratt equations). This review aims to evaluate from recent literature the clinical efficiency and relevance of these equations in terms of bias, precision, and reproducibility in different specific indications (eg, screening CKD, assessment of disease progression, or therapy efficacy) in different populations. Because these prediction equations based on serum creatinine have limitations, especially in the normal or near-normal GFR range, kidney transplant recipients, and pediatric populations, other prediction equations based on serum cystatin C value were also considered as possibly more sensitive GFR surrogate markers. Recent guidelines state that the cystatin C-based prediction equation cannot be recommended for use in clinical practice. With prediction equations based on serum creatinine, the National Kidney Disease Education Program (NKDEP) recommendations are to report a numerical estimate in round numbers only for GFR values <60 mL/min per 1.73 m(2). The MDRD equation generally outperforms the C-G equation but may still have a high level of bias, depending on creatinine assay calibration, and low precision with, at best, approximately 80% of estimated GFR in the "accuracy range" of 70-130% of the measured GFR value, even in patients with known CKD. According to Kidney Disease Improving Global Outcomes (KDIGO) recommendations, many indications remain for GFR measurements using a clearance method. In that context, it should be recalled that radiolabeled-tracer plasma or urinary clearance methods, are safe, simple, accurate and reproducible.

Randomized clinical trial of the effects of methylprednisolone on renal function after major vascular surgery

BACKGROUND

Perioperative renal dysfunction following abdominal aortic aneurysm (AAA) repair is multifactorial and may involve hypotension, hypoxia and ischaemia-reperfusion injury. Studies of cardiac and hepatic transplant surgery have demonstrated beneficial effects on renal function of high-dose methylprednisolone administered before surgery.

METHODS

Twenty patients undergoing elective open AAA repair were randomized to receive either methylprednisolone 10 mg/kg or dextrose (control) before induction of anaesthesia. Blood was analysed for a panel of cytokines representative of T helper cell type 1 and 2 subsets. Urine was analysed for subclinical markers of renal dysfunction (albumin, alpha(1)-microglobulin and N-acetyl-beta-D-glucosaminidase).

RESULTS

Data from 18 patients were analysed. Both groups demonstrated glomerular and proximal convoluted tubular dysfunction that was unaffected by steroid treatment. Steroid administration increased serum levels of urea and creatinine (both P < 0.001). The steroid group had increased interleukin 10 levels (P = 0.005 compared to controls). There were no differences between groups in overall surgical complications, length of intensive care unit (P = 0.821) and hospital (P = 0.719) stay, or 30-day mortality.

CONCLUSION

Methylprednisolone administration altered the cytokine profile favourably but adversely affected postoperative renal function.

Estimated glomerular filtration rate (eGFRCystC) from serum cystatin C shows strong agreement with iohexol clearance in patients with low GFR

OBJECTIVE

Estimation of glomerular filtration rate (eGFR) is essential in the diagnosis and monitoring of patients with kidney disease and for correct dosage of drugs eliminated from the circulation by the kidneys. Cystatin C has been shown in several studies to be superior to creatinine in estimating eGFR. However, there are few studies on the performance of cystatin C estimated eGFR (eGFRCystC) in patients with advanced kidney disease and low GFR.

MATERIAL AND METHODS

We measured serum cystatin C, together with serum creatinine, during iohexol clearance in patients with iohexol clearance below 30 mL/min/1.73 m2. The cystatin C values were used to calculate eGFRCystC using the formula eGFR (mL/min/1.73 m2) = 79.901*(cystatin C value in mg/L)-1.4389.

RESULTS

There was good correlation between eGFRCystC and iohexol clearance (r = 0.88) in patients with iohexol clearance <30 mL/min/1.73 m2 and none of the patients had a difference between eGFRCystC and iohexol clearance exceeding 50 %. The Modification of Diet in Renal Disease (MDRD) equation and corrected MDRD eGFR showed a positive bias and weaker correlations with iohexol eGFR (MDRD = 5.32+1.22*iohexol clearance; corrected MDRD = 4.76+1.10*iohexol clearance; r = 0.59). For MDRD eGFR, 42 of 94 (44.7%) samples showed more than 50% difference to iohexol clearance.

CONCLUSIONS

eGFRCystC is an efficient, practical and cost-effective alternative to iohexol clearance in patients with reduced GFR.

Evaluation of the Modification of Diet in Renal Disease Study Equation in a Large Diverse Population

Glomerular filtration rate (GFR) estimates facilitate detection of chronic kidney disease. Performance of the Modification of Diet in Renal Disease (MDRD) Study equation varies substantially among populations. To describe the performance of the equation in a large, diverse population, estimated GFR (eGFR) was compared to measured GFR (mGFR) in a cross-sectional analysis of 5504 participants in 10 studies that included measurements of standardized serum creatinine and urinary clearance of iothalamate. At eGFR <60 ml/min per 1.73 m(2), the MDRD Study equation had lower bias and higher precision than at eGFR > or =60 ml/min per 1.73 m(2). The accuracy of the equation, measured by the percent of estimates that fell within 30% of mGFR, was similar for eGFR values above or below 60 ml/min per 1.73 m(2) (82% and 84%, respectively). Differences in performance among subgroups defined by age, sex, race, diabetes, transplant status, and body mass index were small when eGFR was <60 ml/min per 1.73 m(2). The MDRD Study equation therefore provides unbiased and reasonably accurate estimates across a wide range of subgroups when eGFR is <60 ml/min per 1.73 m(2). In individual patients, interpretation of GFR estimates near 60 ml/min per 1.73 m(2) should be interpreted with caution to avoid misclassification of chronic kidney disease in the context of the clinical setting.

Amprenavir and didanosine are associated with declining kidney function among patients receiving tenofovir

OBJECTIVE

To examine the effect of antiretroviral agents and clinical factors on the development of tenofovir-associated kidney dysfunction.

METHODS

Observational cohort study of HIV-infected patients receiving tenofovir in an HIV clinic population. Patients' kidney function prior to initiating and while receiving tenofovir was evaluated in relation to other antiretroviral medications and demographic and clinical characteristics. Decline in kidney function was assessed by the glomerular filtration rate (GFR) as estimated by the Cockcroft-Gault (CG) equation, which incorporates weight. Logistic regression analysis was used to examine factors associated with GFR of > 90, 60-90, 30-60, and < 30 ml/min per 1.73 m(2) while on tenofovir. Secondary analyses used the simplified Modification of Diet in Renal Disease (MDRD) equation.

RESULTS

Among the 445 patients initiating tenofovir, 51 (11%) developed a decline in kidney function. In multivariate analysis, there was a significant association between decline in kidney function and concurrent use of amprenavir [odds ratio (OR) 3.6; P = 0.045] and didanosine (OR, 3.1; P = 0.006), age over 50 years (OR, 4.4; P = 0.03), and lower baseline weight (OR, 0.95/kg; P < 0.001). Patients identified with kidney dysfunction by the MDRD equation did not fully overlap with those identified by the CG equation.

CONCLUSIONS

Didanosine and amprenavir use, increased age, and lower baseline weight were significantly associated with risk for kidney dysfunction among patients receiving tenofovir. GFR results using the MDRD equation were inconsistent with those using CG, which highlights the impact of including weight in the estimation of GFR among HIV-infected patients.

Impact of creatinine calibration on performance of GFR estimating equations in a pooled individual patient database

BACKGROUND

Variation in performance of glomerular filtration rate (GFR) estimating equations is related to variation in calibration of the creatinine assay across clinical laboratories.

STUDY DESIGN

Cross-sectional analysis.

SETTING & PARTICIPANTS

6 research studies and 4 clinical populations including 5,504 participants who had GFR measured using urinary clearance of iothalamate.

MEASUREMENTS

Standardized serum creatinine values obtained by means of calibration to the Cleveland Clinic Research Laboratory using frozen specimens, a calibration panel, and/or survey results from the College of American Pathologists.

PREDICTOR

Noncalibrated serum creatinine assayed in research and clinical laboratories compared with standardized serum creatinine.

OUTCOME

Difference between measured GFR versus GFR estimated from the Modification of Diet in Renal Disease (MDRD) Study and Cockcroft-Gault equations.

RESULTS

For a noncalibrated serum creatinine value of 1 mg/dL (88.4 micromol/L), standardized serum creatinine value was 0.07 mg/dL (6.2 micromol/L) less than noncalibrated values. In the pooled data set, for the MDRD Study equation, calibration improved median percentage of difference between measured and estimated GFR from 9.0% (interquartile range [IQR], 28%) to 5.8% (IQR, 28%) and improved the percentage of estimates within 30% of measured GFR (P30) from 80% to 83%. The effect of calibration was greater at higher levels of GFR and varied across studies. For the Cockcroft-Gault equation, calibration worsened the median percentage of difference from -2.0% (IQR, 38%) to -11.4% (IQR, 39%), and the P30, from 74% to 69%.

LIMITATIONS

College of American Pathologist samples were used for calibration of clinical populations; calibration factors do not account for drift over time in the serum creatinine assay; calibration cannot account for variation in assay performance among individuals.

CONCLUSION

Calibration improves the performance of the MDRD Study equation. After calibration, larger errors remain for GFR estimates greater than 60 mL/min/1.73 m2 (>1 mL/s/1.73 m2).

Renal pathophysiology after systemic administration of recombinant adenovirus: changes in renal cytochromes P450 based on vector dose

Recombinant adenovirus (Ad) significantly alters hepatic cytochrome P450 (CYP). Because changes in renal function can alter hepatic CYP, the effect of Ad on renal CYPs 4A1, 4A2, 4F1, and 2E1 was evaluated. Male Sprague-Dawley rats were given one of six intravenous doses (5.7x10(6)-5.7x10(12) viral particles/kg [VP/kg]) of Ad expressing beta-galactosidase or saline. CYP protein, activity, gene expression, and serum creatinine (SCr) were evaluated 0.25, 1, 4, and 14 days later. Doses of 5.7x10(11) and 5.7x10(12) VP/kg increased CYP4A protein within 24 hr by 35 and 48%, respectively (p<0.05). A similar trend was observed on day 4. CYP4A1 mRNA doubled 6 hr after doses of 5.7x10(10)-10(12) VP/kg (p<0.01). Similar effects were observed 1 day after each dose tested. CYP4A2 gene expression was 20% above control 1 day after treatment with 5.7x10(10)-10(12) VP/kg and remained high through day 14. CYP4F1 expression was unaffected by all doses (p=0.08). CYP2E1 activity and gene expression were significantly suppressed 24 hr after administration of all doses and began to normalize by day 14 (p<0.01). SCr was significantly reduced (approximately 50%) throughout the study for doses at and below 5.7x10(11) VP/kg. SCr was increased by a factor of 3 by 5.7x10(12) VP/kg and glomerular filtration was significantly reduced (p<0.01). This suggests that changes in renal CYP and corresponding arachidonic acid metabolites may play a role in the documented toxicity associated with the systemic administration of recombinant Ad.

Reduced kidney function as a risk factor for incident heart failure: the atherosclerosis risk in communities (ARIC) study

Reduced kidney function is a risk factor for cardiovascular morbidity and mortality, and both heart failure (HF) and kidney failure incidences are increasing. This study therefore sought to determine the effect of decreased kidney function on HF incidence in a population-based study of middle-aged adults. From 1987 through 2002, 14,857 participants of the Atherosclerosis Risk in Communities (ARIC) study who were free of prevalent HF at baseline were followed for incident HF hospitalization or death (International Classification of Diseases, Ninth Revision/10th Revision 428/I50). Estimated GFR (eGFR) was calculated using the abbreviated Modification of Diet in Renal Disease (MDRD) Study equation, and kidney function was categorized as normal (eGFR > or =90 ml/min per 1.73 m(2); n = 7143), mildly reduced (eGFR 60 to 89 ml/min per 1.73 m(2); n = 7311), and moderately/severely reduced (eGFR <60 ml/min per 1.73 m(2); n = 403). Cox proportional hazards models were used to control for demographic and cardiovascular risk factors; analyses were stratified by the presence of coronary heart disease at baseline. During a mean follow-up of 13.2 yr, 1193 participants developed HF. The incidence of HF was three-fold higher for individuals with eGFR <60 ml/min per 1.73 m(2) compared to the reference group with eGFR > or =90 ml/min per 1.73 m(2) (18 versus 6 per 1000 person-years). The overall adjusted relative hazard of developing HF was 1.94 (1.49 to 2.53) for individuals with eGFR <60 ml/min per 1.73 m(2) compared to the reference group and was significantly increased for individuals with and without prevalent coronary heart disease at baseline. A substantially greater decline in kidney function occurred in individuals concomitant with HF hospitalization/death compared to those who did not develop HF. In summary, middle-aged adults with moderately/severely reduced kidney function are at high risk for developing HF.

Serum cystatin C as a marker of glomerular filtration rate

PURPOSE OF REVIEW

Glomerular filtration rate is widely accepted as the best overall measure of kidney function. Currently available methods to estimate glomerular filtration rate have strengths and limitations. Cystatin C is a novel endogenous filtration marker being considered as a potential replacement for serum creatinine. This review summarizes the currently available glomerular filtration rate estimating equations based on cystatin C and the literature comparing cystatin C and creatinine as filtration markers.

RECENT FINDINGS

In most cystatin C estimating equations, inclusion of age and sex did not substantially improve their performance. Equations yield different glomerular filtration rate estimates for the same level of cystatin C. Variation among equations may be due to differences among the assays or populations in the individual studies. Studies comparing cystatin C with creatinine or creatinine-based estimating equations show heterogeneous results, with some showing improved performance and others showing equivalent performance even in similar populations. These heterogeneous results may be due to inappropriate comparisons between equations developed in one population with those developed in another, or to the differences between assays or population characteristics.

SUMMARY

Cystatin C shows promise as an alternative to serum creatinine but several important questions remain before it can be recommended for use in clinical practice.

Relation Between Renal Function Within the Normal Range and Central and Peripheral Arterial Stiffness in Hypertension

Chronic kidney disease is accompanied by increased large-artery stiffness, but the relation between glomerular filtration rate within the reference range and central or peripheral arterial stiffness has been understudied. The link between renal function and arterial stiffness was assessed in 305 patients with never-treated essential hypertension (men: 58%; age: 48±11 years, blood pressure: 151/95±20/11 mm Hg), free from overt cardiovascular disease and with serum creatinine values <1.4 mg/dL (men) and <1.2 mg/dL (women), who underwent noninvasive aortic and upper-limb pulse wave velocity (PWV) determination. Aortic PWV was strongly related to age ( r =0.55; P <0.001), whereas upper-limb PWV had a weaker nonlinear relation with age (β=1.392; P <0.001 for age; β=−1.312; P <0.001 for age squared) and a weak relation with aortic PWV ( r =0.22; P <0.001). Glomerular filtration rate (GFR), estimated according to the Mayo clinic equation for healthy subjects, was inversely correlated with large-artery stiffness, as assessed by aortic PWV ( r =−0.34; P <0.001), and with peripheral artery stiffness, as assessed by upper-limb PWV ( r =−0.25; P <0.001). In a multivariate linear regression, aortic PWV was independently predicted by age (β=0.48; P <0.001), mean arterial pressure (β=0.14; P =0.013), and GFR (β=−0.13, P =0.029). Upper-limb PWV was predicted by GFR (β=−0.24; P <0.001) and mean arterial pressure (β=0.20; P <0.001). We conclude that, in hypertensive patients with normal renal function, an inverse relationship exists between GFR and stiffness of both central elastic and peripheral muscular arteries. These relations are in part independent from the effect of several confounders, including age, sex, and blood pressure values.