The importance of standardization of creatinine in the implementation of guidelines and recommendations for CKD: implications for CKD management programmes

Estimated GFR With Cystatin C and Creatinine in Clinical Practice: A Retrospective Cohort Study

Rationale & Objective

Estimation of glomerular filtration rate (eGFR) and staging of chronic kidney disease (CKD) are essential to guide management. Although creatinine is routinely used, a recent national task force recommended the use of cystatin C for confirmation. The objective of this study was to examine the following parameters: (1) how cystatin C correlates with creatinine eGFR; (2) how it indicates differences in CKD staging; and (3) how it may affect kidney care delivery.

Study Design

Retrospective observational cohort study.

Setting & Participants

1,783 inpatients and outpatients who had cystatin C and creatinine levels drawn within 24 hours at Brigham Health-affiliated clinical laboratories.

Predictors

Serum creatinine levels, basic clinical/sociodemographic variables, and reasons for ordering cystatin C from a structured partial chart review.

Analytical Approach

Univariate and multivariable linear and logistic regression.

Results

Cystatin C-based eGFR was very strongly correlated with creatinine-based eGFR (Spearman correlation ρ = 0.83). Cystatin C eGFR resulted in a change to a later CKD stage in 27%, an earlier stage in 7%, and no change in 66% of patients. Black race was associated with a lower likelihood of change to a later stage (OR, 0.53; 95% CI [0.36, 0.75]; P < 0.001), whereas age (OR per year OR, 1.03; 95% CI [1.02, 1.04]; P < 0.001) and Elixhauser score (OR per point OR, 1.22; 95% CI [1.10, 1.36]; P < 0.001) were associated with a higher likelihood of change to a later stage.

Limitations

Single center, no direct measurement of clearance for comparison, and inconsistent self-identification of race/ethnicity.

Conclusions

Cystatin C eGFR correlates strongly with creatinine eGFR but can have a substantial effect on CKD staging. As cystatin C is adopted, clinicians must be informed on this impact.

Clinically relevant urine creatinine underestimation in the low concentration range on the Siemens Dimension Vista®

While considerable efforts have been accomplished to standardize the measurement of plasma creatinine (PCr), urine creatinine (UCr) has not been subject to the same scrutiny. UCr is importantly used when measuring biomarkers in spot urines, to assess urine output and variable dilution of urine samples. Here, we report underestimation of Jaffe UCr measurements on the Siemens Dimension Vista® analyzer, critically affecting samples with UCr ≤2 mmol/L. We demonstrate that this error is caused by automatic urine pre-dilution by the Vista's «urine mode», and that UCr measured in «plasma mode» without pre-dilution does not present this error. In the absence of a comprehensive solution proposed by Siemens, we propose simple formulae that can be easily implemented in a laboratory to correct these low UCr measurements. Importantly, the observed UCr underestimation can significantly influence reported results for biomarkers/UCr ratios measured in spot urine. Indeed, these results can be overestimated up to +84.4 % before correction using our formulae. This can sometimes lead to misclassification according to clinical thresholds, e.g. Kidney disease: improving global outcomes (KDIGO) guidelines for urine albumin/creatinine. This highlights the need for every clinical laboratory to assess the detection limits of their assays, including for lesser-discussed parameters such as UCr. Indeed, the error we reported here may affect other urine assays performing systematic urine pre-dilution and could have significant repercussions on the clinical management of patients.

Adherence to multidisciplinary care in a prospective chronic kidney disease cohort is associated with better outcomes

INTRODUCTION

The Renal Healthcare Program Uruguay (NRHP-UY) is a national, multidisciplinary program that provides care to chronic kidney disease (CKD) patients. In this study, we report the global results of CKD patient outcomes and a comparison between those treated at the NRHP-UY Units, with those patients who were initially included in the program but did not adhere to follow up.

METHODS

A cohort of not-on dialysis CKD patients included prospectively in the NRHP-UY between October 1st 2004 and September 30th 2017 was followed-up until September 30th 2019. Two groups were compared: a) Nephrocare Group: Patients who had at least one clinic visit during the first year on NRHP-UY (n = 11174) and b) Non-adherent Group: Patients who were informed and accepted to be included but had no subsequent data registered after admission (n = 3485). The study was approved by the Ethics Committee and all patients signed an informed consent. Outcomes were studied with Logistic and Cox´s regression analysis, Fine and Gray competitive risk and propensity-score matching tests.

RESULTS

14659 patients were analyzed, median age 70 (60-77) years, 56.9% male. The Nephrocare Group showed improved achievement of therapeutic goals, ESKD was more frequent (HR 2.081, CI 95%1.722-2.514) as planned kidney replacement therapy (KRT) start (OR 2.494, CI95% 1.591-3.910), but mortality and the combined event (death and ESKD) were less frequent (HR 0.671, CI95% 0.628-0.717 and 0.777, CI95% 0.731-0.827) (p = 0.000) compared to the Non-adherent group. Results were similar in the propensity-matched group: ESKD (HR 2.041, CI95% 1.643-2.534); planned kidney replacement therapy (KRT) start (OR 2.191, CI95% 1.322-3.631) death (HR 0.692, CI95% 0.637-0.753); combined event (HR 0.801, CI95% 0.742-0.865) (p = 0.000).

CONCLUSION

Multidisciplinary care within the NRHP-UY is associated with timely initiation of KRT and lower mortality in single outcomes, combined analysis, and propensity-matched analysis.

Serum Total SOD Activity and SOD1/2 Concentrations in Predicting All-Cause Mortality in Lung Cancer Patients

Redox status disturbances are known during carcinogenesis and may have influence on patients' survival. However, the prediction of mortality in lung cancer patients based on serum total SOD activity, and concentrations of its isoforms, has not been studied to date. This prospective cohort study has following aims: (1) to evaluate the disturbances in serum SOD activity and SOD1/2 concentrations; (2) to assess the implications of these alterations with regard to biochemical variables and clinical data, and (3) to investigate the association between serum SOD activity, SOD1/2 concentrations, and all-cause mortality in lung cancer patients. Serum total SOD activity and SOD1, SOD2, albumin, CRP, and ceruloplasmin concentrations were determined in lung cancer patients (n = 190) and control subjects (n = 52). Additionally, patients were characterized in terms of biochemical, clinical, and sociodemographic data. Multiple Cox regression models were used to estimate the association between all-cause death and SOD-related parameters. All-cause mortality in lung cancer was positively associated with serum SOD1 and SOD2 concentrations. Clinical stage III and IV disease was the strongest predictor. The utility of the evaluated parameters in predicting overall survival was demonstrated only for SOD1. Serum SOD1 and SOD2 concentrations were shown to positively affect all-cause mortality in lung cancer patients, but SOD1 seems to be a better predictor than SOD2.

Serum and Whole Blood Cu and Zn Status in Predicting Mortality in Lung Cancer Patients

Alterations in circulating Cu and Zn are negative predictors of survival in neoplastic patients and are known during lung cancer. However, no data on predicting mortality of lung cancer patients based on the level of these elements in the blood have been presented to date. The aims of this prospective cohort study were as follows: (i) To evaluate the disturbances in serum and whole blood Cu and Zn, (ii) to assess the relationships between serum and whole blood Cu and Zn status and clinical, sociodemographic, and nutritional data, and (iii) to investigate the association of Cu and Zn status with all-cause mortality in lung cancer. Naïve-treatment lung cancer patients (n = 167) were characterized in terms of sociodemographic, clinical, and anthropometric data and dietary intake and compared with sex-matched control subjects (n = 48). Whole blood and serum Cu and Zn status was determined by atomic absorption spectrometry. Cox proportional hazards models adjusted for multiple confounders/mediators were used to estimate the association between all-cause death and Cu and Zn status. Sex, cardiovascular disease, chronic obstructive pulmonary disease, clinical stage, and hemoglobin, platelet, and glucose concentrations significantly differentiated Cu and Zn status. All-cause mortality in lung cancer patients was positively associated with serum Cu levels, Cu:Zn ratio, and whole blood Zn levels. However, an advanced clinical stage of disease was the strongest predictor of all-cause mortality. Circulatory status of Cu and Zn might be included in routine clinical characteristics of patients with lung cancer patients as additional prognostic variables, but only after further more detail studies.

The prevalence of chronic kidney disease in Iceland according to KDIGO criteria and age-adapted estimated glomerular filtration rate thresholds

Most epidemiological studies on chronic kidney disease (CKD) are based solely on estimated glomerular filtration rate (eGFR). Few studies have included proteinuria, while the chronicity criterion is usually omitted. To explore this, we examined the prevalence of CKD stages 1-5 in Iceland based on multiple markers of kidney damage. All serum creatinine values, urine protein measurements and diagnostic codes for kidney diseases and comorbid conditions for people aged 18 years and older were obtained from electronic medical records of all healthcare institutions in Iceland in 2008-2016. CKD was defined according to the Kidney Disease: Improving Global Outcomes (KDIGO) clinical practice guideline using diagnoses indicative of a chronic kidney disease, proteinuria and/or an eGFR under 60 mL/min/1.73 m² for over three months. Mean annual age-standardized prevalence of CKD stages 1-5 was calculated based on the KDIGO criteria and age-adapted eGFR thresholds from 2,120,147 creatinine values for 218,437 individuals, 306,531 proteinuria measurements for 86,364 individuals and 6973 individuals carrying a kidney disease diagnosis. Median age was 63 years (range, 18-106) and 47% were male. The mean annual age standardized CKD prevalence was 5.13% for men and 6.75% for women using the KDIGO criteria but by age-adapted eGFR cut-offs, the prevalence was 3.27% for men and 4.01% for women. Thus, our nationwide study, defining CKD in Iceland with strict adherence to the KDIGO criteria, demonstrates a lower prevalence of CKD than anticipated from most previous studies.

Impact of superimposed nephrological care to guidelines-directed management by primary care physicians of patients with stable chronic kidney disease: a randomized controlled trial

BACKGROUND

Optimal clinical care of patients with chronic kidney disease (CKD) requires collaboration between primary care physicians (PCPs) and nephrologists. We undertook a randomised trial to determine the impact of superimposed nephrologist care compared to guidelines-directed management by PCPs in CKD patients after hospital discharge.

METHODS

Stage 3b-4 CKD patients were enrolled during a hospitalization and randomised in two arms: Co-management by PCPs and nephrologists (interventional arm) versus management by PCPs with written instructions and consultations by nephrologists on demand (standard care). Our primary outcome was death or rehospitalisation within the 2 years post-randomisation. Secondary outcomes were: urgent renal replacement therapy (RRT), decline of renal function and decrease of quality of life at 2 years.

RESULTS

From November 2009 to the end of June 2013, we randomised 242 patients. Mean follow-up was 51 + 20 months. Survival without rehospitalisation, GFR decline and elective dialysis initiation did not differ between the two arms. Quality of life was also similar in both groups. Compared to randomised patients, those who either declined to participate in the study or were previously known by nephrologists had a worse survival.

CONCLUSION

These results do not demonstrate a benefit of a regular renal care compared to guided PCPs care in terms of survival or dialysis initiation in CKD patients. Increased awareness of renal disease management among PCPs may be as effective as a co-management by PCPs and nephrologists in order to improve the prognosis of moderate-to-severe CKD.

TRIAL REGISTRATION

This study was registered on June 29, 2009 in clinicaltrials.gov (NCT00929760) and adheres to CONSORT 2010 guidelines.

Recalibration of cystatin C using standardized material in Siemens nephelometers

BACKGROUND

Cystatin C is a key GFR biomarker. Recently, Siemens recalibrated the assay based on certified reference material ERM-DA471/IFCC. The NIH-funded longitudinal chronic kidney disease in children (CKiD) study has > 3000 cystatin C measurements based on a pre-IFCC calibrator provided by Siemens. Since cystatin C values for CKiD are now standardized to IFCC certified reference material, it is important to relate the IFCC-calibrated results to the previous values so that there are no discontinuous results.

METHODS

We diluted cystatin C ERM-DA471/IFCC (5.48 mg/L) into buffer and compared results with predicted ones. We then updated the cystatin C application on our BN II nephelometer to provide results based on pre-IFCC and IFCC calibrations of CKiD specimens simultaneously. We assayed 51 previously analyzed sera and 62 fresh additional specimens.

RESULTS

The predicted concentrations from the IFCC standard were consistently 17% higher than the measured values using the pre-IFCC calibration (y = 1.1686x). Similarly, the re-run and fresh sample concentrations were 17% higher via the IFCC calibration than by the pre-IFCC calibration (y = 1.168x). There was very high reliability in the measurements using the previous calibration for re-run specimens (0.99) and for 33 pristine specimens using IFCC calibration (0.99).

CONCLUSIONS

We confirm the recalibration proposed by Siemens. To convert pre-IFCC results to IFCC-calibrated concentrations, the value is multiplied by 1.17. Conversely, one divides IFCC-calibrated results by 1.17 to estimate GFR via previously published pre-IFCC CKiD eGFR equations. For older adolescents, cystatin C has already been standardized and can be directly applied to the CKD-EPI equations.

Physicochemical Contents, Antioxidant Activities, and Acute Toxicity Assessment of Selenium-Enriched Chinese Kale (Brassica oleracea var. alboglabra L.) Seedlings

The oxidative activities of hydroponically produced Chinese kale (Brassica oleracea var. alboglabra L.) seedlings grown under different concentrations of selenium (Se) biofortification with sodium selenite (Na2SeO3) at 0, 5, 10, 15, and 30 mg·Se/L and different ages (5, 10, and 15 days after germination) were determined by the electron transfer method (DPPH and FTC). Highest antioxidant activities of Se-enriched Chinese kale seedlings (Se-KS) were found in seedlings grown on 30 mg·Se/L, 15 days after germination. The physicochemical contents (moisture, crude fibre, ash, crude protein, and carbohydrate), total Se contents, and Se bioaccessibility and antioxidant activities (after treatment with an in vitro simulated gastrointestinal digestion process) between Se-KS and a control of regular Chinese kale seedlings (R-KS) were compared. The crude protein and total Se contents of the air-dried matter in Se-KS were higher (37 ± 1% and 433 ± 22 mg·Se/kg) than those of the R-KS (33 ± 2% and 17 ± 3 mg·Se/kg). Total Se content and antioxidant activities were strongly correlated in the range from 0.93 to 0.99. Testing acute toxicity, a single dose of the Se-KS was orally administrated to rats at 1250, 2500, and 5000 mg/kg·b.w., which consisted of 0.54, 1.08, and 2.16 mg Se/kg·b.w., respectively. These results demonstrated that Se-KS did not create any toxicological signs and mortality. No abnormal pathological changes in the liver, kidney, and heart were found. The results suggested that the Se-KS could be a good source of organo Se for development as a new Se supplementary product.

Standardization in laboratory medicine: Adoption of common reference intervals to the Croatian population

Considering the fact that the results of laboratory tests provide useful information about the state of health of patients, determination of reference value is considered an intrinsic part in the development of laboratory medicine. There are still huge differences in the analytical methods used as well as in the associated reference intervals which could consequently significantly affect the proper assessment of patient health. In a constant effort to increase the quality of patients’ care, there are numerous international initiatives for standardization and/or harmonization of laboratory diagnostics in order to achieve maximum comparability of laboratory test results and improve patient safety. Through the standardization and harmonization processes of analytical methods the ability to create unique reference intervals is achieved. Such reference intervals could be applied globally in all laboratories using methods traceable to the same reference measuring system and analysing the biological samples from the populations with similar socio-demographic and ethnic characteristics. In this review we outlined the results of the harmonization processes in Croatia in the field of population based reference intervals for clinically relevant blood and serum constituents which are in accordance with ongoing activity for worldwide standardization and harmonization based on traceability in laboratory medicine.

Methodology used in studies reporting chronic kidney disease prevalence: a systematic literature review

Background

Many publications report the prevalence of chronic kidney disease (CKD) in the general population. Comparisons across studies are hampered as CKD prevalence estimations are influenced by study population characteristics and laboratory methods.

Methods

For this systematic review, two researchers independently searched PubMed, MEDLINE and EMBASE to identify all original research articles that were published between 1 January 2003 and 1 November 2014 reporting the prevalence of CKD in the European adult general population. Data on study methodology and reporting of CKD prevalence results were independently extracted by two researchers.

Results

We identified 82 eligible publications and included 48 publications of individual studies for the data extraction. There was considerable variation in population sample selection. The majority of studies did not report the sampling frame used, and the response ranged from 10 to 87%. With regard to the assessment of kidney function, 67% used a Jaffe assay, whereas 13% used the enzymatic assay for creatinine determination. Isotope dilution mass spectrometry calibration was used in 29%. The CKD-EPI (52%) and MDRD (75%) equations were most often used to estimate glomerular filtration rate (GFR). CKD was defined as estimated GFR (eGFR) <60 mL/min/1.73 m² in 92% of studies. Urinary markers of CKD were assessed in 60% of the studies. CKD prevalence was reported by sex and age strata in 54 and 50% of the studies, respectively. In publications with a primary objective of reporting CKD prevalence, 39% reported a 95% confidence interval.

Conclusions

The findings from this systematic review showed considerable variation in methods for sampling the general population and assessment of kidney function across studies reporting CKD prevalence. These results are utilized to provide recommendations to help optimize both the design and the reporting of future CKD prevalence studies, which will enhance comparability of study results.

Cystatin C standardization decreases assay variation and improves assessment of glomerular filtration rate

BACKGROUND

Cystatin C is increasingly used in glomerular filtration rate (GFR) estimation equations. The dependence of cystatin C results upon the analytical method has been a major source of controversy.

METHODS

Cystatin C was measured with non-standardized turbidimetric Roche Generation 1 and standardized nephelometric Siemens assays in 3666 and additionally with standardized Roche Generation 2 and Siemens in 567 blood samples of the Berlin Initiative Study. Cystatin C-based GFR was assessed with CKD-EPIcys (Chronic Kidney Disease Epidemiology) and CAPA (Caucasian, Asian, Pediatric, Adult) equations and the impact of the assays on GFR estimation was determined. Equation performance compared to measured GFR was evaluated.

RESULTS

Concordance of Roche Gen2 and Siemens was high with median difference of 0.003 ± 0.13 mg/L (limits of agreement: -0.12 to 0.12) and Passing Bablok correlation was essentially perfect. Roche Gen1 assay showed worse concordance with Siemens: median difference was 0.08 ± 0.13 mg/L (limits of agreement: -0.18 to 0.34) and correlation was inferior. Mean difference (± SD) of estimated GFRCKD-EPIcys was 0 ± 4 mL/min/1.73 m(2) for Gen2 and Siemens compared to -5 ± 8 with Gen1. Performance of GFR estimating equations was not influenced by the choice of Siemens or Gen2 assays.

CONCLUSIONS

Standardization of Roche Gen2 assay improved accuracy of cystatin C measurement compared to Siemens. It suggests only negligible method bias and results in equal performance of both assays when estimating GFR indicating that successful calibration has led to major progress in cystatin C analysis.

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

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

Calibration and precision of serum creatinine and plasma cystatin C measurement: impact on the estimation of glomerular filtration rate

Serum creatinine (SCr) is the main variable for estimating glomerular filtration rate (GFR). Due to inter-assay differences, the prevalence of chronic kidney disease (CKD) varies according to the assay used, and calibration standardization is necessary. For SCr, isotope dilution mass spectrometry (IDMS) is the gold standard. Systematic differences are observed between Jaffe and enzymatic methods. Manufacturers subtract 0.30 mg/dl from Jaffe results to match enzymatic results ('compensated Jaffe method'). The analytical performance of enzymatic methods is superior to that of Jaffe methods. In the original Modification of Diet in Renal Disease (MDRD) equation, SCr was measured by a Jaffe Beckman assay, which was later recalibrated. A limitation of this equation was an underestimation of GFR in the high range. The Chronic Kidney Disease Epidemiology (CKD-EPI) consortium proposed an equation using calibrated and IDMS traceable SCr. The gain in performance was due to improving the bias whereas the precision was comparable. The CKD-EPI equation performs better at high GFR levels (GFR >60 ml/min/1.73 m(2)). Analytical limitations have led to the recommendation to give a grade (>60 ml/min/1.73 m(2)) rather than an absolute value with the MDRD equation. By using both enzymatic and calibrated methods, this cutoff-grade could be increased to 90 ml/min/1.73 m(2) (with MDRD) and 120 ml/min/1.73 m(2) (with CKD-EPI). The superiority of the CKD-EPI equation over MDRD is analytical, but the precision gain is limited. IDMS traceable enzymatic methods have been used in the development of the Lund-Malmö (in CKD populations) and Berlin Initiative Study equations (in the elderly). The analytical errors for cystatin C are grossly comparable to issues found with SCr. Standardization is available since 2011. A reference method for cystatin C is still lacking. Equations based on standardized cystatin C or cystatin C and creatinine have been proposed. The better performance of these equations (especially the combined CKD-EPI equation) has been demonstrated.

The impact of introducing automated eGFR reporting on uncovering new cases of chronic kidney disease in a University Hospital in Saudi Arabia

OBJECTIVE

To determine the impact of introducing eGFR automated reporting on uncovering new cases of Chronic Kidney Disease.

METHODS

All serum creatinine (SCr) in adult patients attending outpatient clinics over a two-month period were recorded and eGFR estimated. Cases with a SCr within normal limits but were in CKD stage 3 (<60 mL/min) or higher were recorded and their numbers, percentages and mean ages calculated. Stages 1 and 2 were excluded from analysis because urinary albumin and other urinary abnormalities were not checked.

RESULTS

A total of 26,422 SCr from different patients were included. The mean SCr was 92.5 ± 130.9 μmol/ and the mean eGFR was 99.8 ± 32.4 mL/min/1.73 m(2). Of all the10,601 males with normal SCr, 0.84% were in CKD stage 3 and in all the 14,695 female, 19.24% were in stage 2 in stage. Of all the 14,695 females with serum creatinine in the normal range, 200 (1.36%) were in CKD stage 3. The patients in stages 2 and 3 were significantly older.

CONCLUSION

If our findings are shown to be true for the rest of Saudi Arabia, one could extrapolate that for each 100,000 serum creatinine assayed for males, 840 new cases will be uncovered in CKD stage 3. The corresponding number for females would be 1360 cases.

Variability of glomerular filtration rate estimation equations in elderly Chinese patients with chronic kidney disease

Background

Chronic kidney disease (CKD) is recognized worldwide as a public health problem, and its prevalence increases as the population ages. However, the applicability of formulas for estimating the glomerular filtration rate (GFR) based on serum creatinine (SC) levels in elderly Chinese patients with CKD is limited.

Materials and methods

Based on values obtained with the technetium-99m diethylenetriaminepentaacetic acid (^99mTc-DTPA) renal dynamic imaging method, 319 elderly Chinese patients with CKD were enrolled in this study. Serum creatinine was determined by the enzymatic method. The GFR was estimated using the Cockroft–Gault (CG) equation, the Modification of Diet in Renal Disease (MDRD) equations, the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation, the Jelliffe-1973 equation, and the Hull equation.

Results

The median of difference ranged from −0.3–4.3 mL/min/1.73 m². The interquartile range (IQR) of differences ranged from 13.9–17.6 mL/min/1.73 m². Accuracy with a deviation less than 15% ranged from 27.6%–32.9%. Accuracy with a deviation less than 30% ranged from 53.6%–57.7%. Accuracy with a deviation less than 50% ranged from 74.9%–81.5%. None of the equations had accuracy up to the 70% level with a deviation less than 30% from the standard glomerular filtration rate (sGFR). Bland–Altman analysis demonstrated that the mean difference ranged from −3.0–2.4 mL/min/1.73 m². However, the agreement limits of all the equations, except the CG equation, exceeded the prior acceptable tolerances defined as 60 mL/min/1.73 m². When the overall performance and accuracy were compared in different stages of CKD, GFR estimated using the CG equation showed promising results.

Conclusions

Our study indicated that none of these equations were suitable for estimating GFR in the elderly Chinese population investigated. At present, based on overall performance, as well as performance in different CKD stages, the CG equation may be the most accurate for estimating GFR in elderly Chinese patients with CKD.

Outcomes of early versus late nephrology referral in chronic kidney disease: a systematic review

BACKGROUND

As late provision of specialist care, before starting dialysis therapy, is believed to be associated with increased morbidity and mortality, a systematic review was undertaken to evaluate clinical outcomes relating to early versus late referral of patients to nephrology services.

METHODS

Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, and EMBASE were searched up until September 2008 for studies of early versus late nephrology referral in adult (>18 years) patients with chronic kidney disease. Early referral was defined by the time period at which patients were referred to a nephrologist.

FINDINGS

No randomized controlled trials were found. Twenty-seven longitudinal cohort studies were included in the final review, providing data on 17,646 participants; 11,734 were referred early and 5912 (33%) referred late. Comparative mortality was higher in patients referred to a specialist late versus those referred early. Odds ratios (OR) for mortality reductions in patients referred early were evident at 3 months (OR 0.51; 95% confidence interval [CI], 0.44-0.59) and remained at 5 years (OR 0.45; 95% CI, 0.38-0.53), both P <.00001. Initial hospitalization was 8.8 days shorter with early referral (95% CI, -10.7 to -7.0 days; P <.00001). Differences in mortality and hospitalization data between the 2 groups were not explained by differences in prevalence of diabetes mellitus, previous coronary artery disease, blood pressure control, serum phosphate, and serum albumin. However, early referral was associated with better preparation and placement of dialysis access.

CONCLUSION

Our analyses show reduced mortality and hospitalization, better uptake of peritoneal dialysis, and earlier placement of arteriovenous fistula for hemodialysis with early nephrology referral.

A multicentric evaluation of IDMS-traceable creatinine enzymatic assays

Chronic kidney disease definition is based on glomerular filtration rate (GFR) estimations which are derived from creatinine-based equations. The accuracy of GFR estimation is thus largely dependent of those of serum creatinine assays. International recommendations highlight the need for traceable creatinine assays. The French Society of Clinical Biochemistry conducted a study for measuring accuracy of creatinine enzymatic methods. This evaluation involved 25 clinical laboratories. Creatinine was measured in serum pools ranging from 35.9±0.9 μmol/L to 174.5±3.1 μmol/L (IDMS determination) using 12 creatinine enzymatic methods. For all creatinine values greater than 74.4±1.4 μmol/L, the bias and imprecision did not exceed 5% and 5.9%, respectively. For the lowest value (35.9±0.9 μmol/L), the bias ranged from -1.8 to 9.9% (with one exception). At this level, the imprecision ranged from 1.9 to 7.8%. The true performances of the assays (couples of bias and relative standard deviation), were evaluated using Monte-Carlo simulations. Most of the assays fall within the maximum Total Error of 12% at all concentrations. This study demonstrates substantial improvements in the calibration, traceability and precision of the enzymatic methods, reaching the NKDEP recommendations. Moreover, most of these assays allowed accurate creatinine measurements for creatinine levels lower than 40 μmol/L.

Focusing on the clinical impact of standardization of creatinine measurements: a report by the EFCC Working Group on Creatinine Standardization

The recent campaign for standardization of creatinine measurements has been promoted to allow the widespread use of formulas for estimating the glomerular filtration rate (GFR). However, studies on trueness verification and measurement interferences still show disappointing interassay variation of serum creatinine results. Creatinine recalibration has major clinical consequences. In particular, in pediatrics where reference ranges for serum and plasma creatinine are low, calculation of the GFR is problematic when based on alkaline picrate methods because of method non-specificity and the lack of appropriate GFR estimating formulas. Therefore, enzymatic creatinine assays are preferred. In the near future, cystatin C might offer an interesting alternative for GFR estimation. For the calculation of drug doses, the Modification of Diet in Renal Disease study formula generally offers reliable data. However, attention has to be paid to the elderly. Also, the calculation of the Model for End-Stage Liver Disease score, which is used to prioritize patients for liver transplantation, may significantly be influenced by recalibration of creatinine assays. Creatinine restandardization may also affect the current guidelines for referral of chronic kidney disease patients to nephrologists.

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.

Estimated glomerular filtration rate, chronic kidney disease and antiretroviral drug use in HIV-positive patients

OBJECTIVES

Chronic kidney disease (CKD) in HIV-positive persons might be caused by both HIV and traditional or non-HIV-related factors. Our objective was to investigate long-term exposure to specific antiretroviral drugs and CKD.

DESIGN

A cohort study including 6843 HIV-positive persons with at least three serum creatinine measurements and corresponding body weight measurements from 2004 onwards.

METHODS

CKD was defined as either confirmed (two measurements >or=3 months apart) estimated glomerular filtration rate (eGFR) of 60 ml/min per 1.73 m or below for persons with baseline eGFR of above 60 ml/min per 1.73 m or confirmed 25% decline in eGFR for persons with baseline eGFR of 60 ml/min per 1.73 m or less, using the Cockcroft-Gault formula. Poisson regression was used to determine factors associated with CKD.

RESULTS

Two hundred and twenty-five (3.3%) persons progressed to CKD during 21 482 person-years follow-up, an incidence of 1.05 per 100 person-years follow-up [95% confidence interval (CI) 0.91-1.18]; median follow-up was 3.7 years (interquartile range 2.8-5.7). After adjustment for traditional factors associated with CKD and other confounding variables, increasing cumulative exposure to tenofovir [incidence rate ratio (IRR) per year 1.16, 95% CI 1.06-1.25, P < 0.0001), indinavir (IRR 1.12, 95% CI 1.06-1.18, P < 0.0001), atazanavir (IRR 1.21, 95% CI 1.09-1.34, P = 0.0003) and lopinavir/r (IRR 1.08, 95% CI 1.01-1.16, P = 0.030) were associated with a significantly increased rate of CKD. Consistent results were observed in wide-ranging sensitivity analyses, although of marginal statistical significance for lopinavir/r. No other antiretroviral drugs were associated with increased incidence of CKD.

CONCLUSION

In this nonrandomized large cohort, increasing exposure to tenofovir was associated with a higher incidence of CKD, as was true for indinavir and atazanavir, whereas the results for lopinavir/r were less clear.

Cystatin C as a marker of acute kidney injury in the emergency department

BACKGROUND AND OBJECTIVES

The diagnosis of acute kidney injury (AKI) is usually based on changes in serum creatinine, which is a poor marker of early renal dysfunction. The discriminative and predictive abilities of serum and urinary cystatin C were examined for the prediction of AKI.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

In this prospective cohort study, serum and urinary cystatin C were serially measured in a heterogeneous group of patients (n = 616) presenting to a tertiary care emergency department. The primary outcome was AKI, classified according to RIFLE and AKIN criteria. The secondary outcome was an adjudication based on clinical criteria to AKI, prerenal azotemia, chronic kidney disease (CKD), and normal kidney function.

RESULTS

Patients were adjudicated to have AKI in 21.1%, prerenal azotemia in 25.8%, CKD in 2.4%, and normal kidney function in 50.7%. For the diagnosis of AKI, the discriminatory ability of urinary creatinine and cystatin C was marginal. Both serum cystatin C and serum creatinine (at presentation and 6 hours later) showed high discriminatory ability for the diagnosis of AKI. However, only serum cystatin C attained a significant early predictive power (Hosmer-Lemeshow P value > 0.05). Serum cystatin C could differentiate between AKI and prerenal azotemia, but not between AKI and CKD.

CONCLUSIONS

Serum cystatin C is an early, predictive biomarker of AKI, which outperforms serum creatinine in the heterogeneous emergency department setting. However, neither biomarker discriminated between AKI and CKD. Additional biomarkers continue to be needed for improved specificity in the diagnosis of community-acquired AKI.

Applicability of common reference intervals for serum creatinine concentrations to the Croatian population

BACKGROUND

In accordance with an ongoing activity for worldwide harmonization based on traceability in laboratory methods, the goal of this study was to validate the applicability of recommended "common" reference intervals for serum creatinine concentrations using a specific enzymatic method to the Croatian population.

METHODS

The reference group consisted of 240 healthy subjects (120 males and 120 females), between 18 and 74 years of age (median 57 years), who were selected in accordance with the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) recommendations. Creatinine in serum was measured using the creatinine enzymatic assay (Olympus OSR61204) that was standardized to the isotopic dilution mass spectrometry (IDMS) method and National Institute of Standards and Technology (NIST) Standard Reference Material (SRM) 967. In addition, creatinine was measured using a kinetic Jaffe method (Olympus OSR6178) standardized to NIST SRM 909b level 2 standard.

RESULTS

Method comparison between enzymatic creatinine (x) and the Jaffe kinetic method (y) gave the following P/B equation for the entire group (n=240): y=1.00x+17.00; r=0.968. Reference intervals for serum creatinine (central 95th percentiles) obtained using the enzymatic creatinine method ranged from 54 to 107 micromol/L for males and from 50 to 93 micromol/L for females. The IFCC recommended common reference intervals for global applications are 64-104 micromol/L and 49-90 micromol/L for males and females, respectively.

CONCLUSIONS

Comparability of obtained results confirmed the applicability of recently recommended "common" reference intervals to the Croatian population for all laboratories measuring serum creatinine concentrations using enzymatic methods traceable to the IDMS method and NIST SRM 967.

Referral of patients with kidney impairment for specialist care in a developing country of sub-Saharan Africa

AIM

The aim of this study was to assess the referral pattern of patients with kidney impairment in Cameroon.

METHODS

Medical files of patients received at the out-patients department of nephrology from January 2001 to December 2003 at the Yaounde General Hospital were reviewed. Individual information recorded included age, sex, and referral sources. Data on etiologic and co-morbidity factors, clinical signs of CRF, anthropometric measurements, blood pressure, and biological variables were recorded. Patients were staged for kidney damage in three groups following an adaptation of the Kidney Disease Outcome Quality Initiative (KDOQI) guide recommendations, using the creatinine clearance derived from the Cockroft-Gault equation.

RESULTS

Of the 183 patients received during the study period, 140 (77.8%) fulfilled the entry criteria. Men (70%) were more represented, and mean age was 50.19 +/- 1.07 years. Hypertension (62.1%) and diabetes mellitus (26.4%) were the most frequent risk factors. There was no major difference between men and women for most clinical and biological variables. Patients were referred mostly by cardiologist (31.4%) and general practitioners (29.3%). Late referral (GFR <30 mL/min) encompassed 82.8% of participants. Regardless of the referral source, the overall trend was toward late referral. Clinical and biological profiles worsen with advanced stage of kidney impairment. In general, management of patients prior to referral was poor.

CONCLUSIONS

This study has revealed the disconcerting high rate of late referral to nephrologists in this context. Many potential factors can account for this observed pattern, and it is worth investigating to improve referral and outcomes of patients with kidney diseases in Cameroon.

Natural history of CKD stage 4 and 5 patients following referral to renal management clinic

BACKGROUND

CKD patients referred to a renal management clinic are looked after by a multidisciplinary team whose care may improve outcome and delay the progression of kidney disease. This paper describes our experience and the results obtained in 940 patients with CKD stage 4 and 5 patients from two renal management clinics (RMC).

SUBJECTS AND METHODS

We collected and analyzed the data from 940 patients with CKD stage 4 and 5 at the RMCs of the Toronto General Hospital (TGH), University Health Network and The Scarborough General Hospital (TSH) from January 2000 to November 2007. Inclusion criteria for the study required at least three measurements of serum creatinine over a minimum follow-up of 6 months. We calculated the change of slope of the estimated GFR by linear regression analysis. The slopes were further subdivided into five groups: improved eGFR (eGFR slope >or=+5 ml/min/year); mild improvement (slope >+1 to <+5 ml/min/year); stable (slope <+1 to >-1 ml/min/year); slow progression (i.e., deterioration; slope <-1 to >-5 ml/min/year) and rapid progression (slope >-5 ml/min/year).

RESULTS

During a median follow-up of 1.57 year (range 0.5-8.7 year) of stage 4 patients, eGFR improved in 10.6%, showed mild improvement in 24.2%, was stable in 27.5%, showed slow progression in 28.8% and rapid progression in 8.9% of patients. During a median follow-up of 1.4 year (range 0.5-8 year) of CKD stage 5 patients, eGFR improved in only 1.3%, showed mild improvement in 4.3%, remained stable in 35.6%; showed slow progression in 19.7% and rapid progression in 39.1%. Between the two hospitals (TGH and TSH) there was a statistically significant difference in the number of visits per year for CKD stage 4 patients during the first, second and third year. However, the number of visits per year had no effect on the rate of decline. On univariate analysis, factors predicting non-progression in eGFR slope were eGFR at referral, the use of ACE inhibitors-ARBs and absence of cardiovascular disease. However, in logistic multivariate regression analysis, after adjusting for confounding factors only the eGFR at referral and ACE inhibitors-ARBs were independent factors for non-progression in eGFR. A significant percentage of CKD stage 4 patients attending a renal management clinic (RMC) showed non-progression or improvement in their kidney function. Although only few stage 5 CKD patients had improvement in their eGFR, 32% of them maintained their eGFR on conservative treatment for over 2 years delaying the initiation of dialysis.

Estimating glomerular filtration rate: Cockcroft-Gault and Modification of Diet in Renal Disease formulas compared to renal inulin clearance

BACKGROUND AND OBJECTIVES

Evaluation of renal function by estimation of the glomerular filtration rate (GFR) is very important for the diagnosis and treatment of patients with chronic kidney disease (CKD). The Cockcroft-Gault (CG) and Modification of Diet in Renal Disease (MDRD) formulas are the most commonly used estimations.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Estimated GFR values by each formula were compared with measured GFR (mGFR) by renal inulin clearance in 2208 European adults (46% women, 1.4% Caribbean blacks), with and without CKD, and mean mGFR 72.4 +/- 39.0 (range 2.2 to 177.2) ml/min/1.73 m(2).

RESULTS

Overall, the CG and MDRD formulas showed bias (mean difference) -3.5 ml/min/1.73 m(2) (5.3%), P < 0.001, and -9.8 ml/min/1.73 m(2) (-6.4%), P < 0.001; precision (SD of bias) 21.5 ml/min/1.73 m(2) (43.1%) and 20.0 ml/min/1.73 m(2) (33.0%); limits of agreement (2 SD by Bland-Altman method) 39.5 to -46.5 (range 86.0) ml/min/1.73 m(2) and 30.2 to -49.8 (range 80.0) ml/min/1.73 m(2); and accuracy within +/-30% of mGFR 70.8 and 69.0%, respectively. Both formulas showed a trend for decreasing accuracy with lower mGFR levels. According to the Kidney Disease Outcomes Quality Initiative (K/DOQI)-CKD classification's five GFR groups, the CG and MDRD formulas properly assigned 61.6 and 57.1% of the entire population and had a range of positive predictive values 42.6 to 81.8% and 39.6 to 85.2% and of negative predictive values 81.7 to 96.6% and 76.4 to 97.5%, respectively.

CONCLUSIONS

The CG and MDRD formulas had some limitations for proper GFR estimation and K/DOQI-CKD classification by GFR levels alone.

Late referral of patients with end-stage renal disease: an in-depth review and suggestions for further actions

Late referral of patients with chronic kidney disease (CKD) is a known problem and a major challenge for practising nephrologists since decades. In this review we report about the reasons for late referral, its epidemiology and socioeconomic impact and the medical particularities of late referred patients. We furthermore highlight on the efforts which have been undertaken so far to avoid late referral and should be undertaken in future to face the ever growing numbers of chronic kidney disease patients.

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.

Analytical study of three cystatin C assays and their impact on cystatin C-based GFR-prediction equations

BACKGROUND

Cystatin C-based equations are used to estimate GFR. However, three cystatin C immunoassays are on the market. Difference in cystatin C assays could have strong consequences on the accuracy and precision of cystatin C-based equations. We have performed an analytical study of these three assays and studied potential differences between assays on the precision of cystatin C-based equations.

METHODS

We have studied imprecision, recovery, linearity and interferences of the three immunoassays (nephelometric assay from Siemens and turbidimetric assays from Dako and Gentian). The impact of differences in cystatin C assays has been studied for the equations published by Levey (Siemens assay) and Grubb (Dako assay).

RESULTS

Analytical performance of the Dako assay is slightly less high. For cystatin C values below 2.5 mg/L, no statistical difference is found between results given by the Dako and the Gentian assays. So, both assays can be used in the Grubb equation. Cystatin C results are different with the Siemens assay. The Levey equation, built with the Siemens assay, can only be used with cystatin C values measured with this assay. Using the Dako or Gentian assay results in the Levey equation can lead to differences in estimating GFR up to 6 mL/min/1.73 m2. Differences can reach 9.5 mL/min/1.73 m2 if the Siemens assay is used in the Grubb equation.

CONCLUSION

The Siemens and Gentian assays seem analytically more valid than the Dako assay for cystatin C determination. Differences in cystatin C assays can lead to significant differences in cystatin C-based equations. However, these differences seem less important than the differences observed with creatinine and creatinine-based equations.

Establishing a renal management clinic in China: initiative, challenges, and opportunities

BACKGROUND

Chronic kidney disease (CKD) has been identified as a growing global burden and traditional health care systems are inadequate for the management of CKD patients. This paper describes an initiative to establish a renal management clinic (RMC) in China and discusses the challenges and opportunities in the management of CKD patients.

SUBJECTS AND METHODS

We collected and analyzed the data for the first 1,000 CKD patients treated since the establishment of the RMC (from April 2006 to April 2007). They had CKD stages 1-4 and stage 5 (before dialysis), as described by the Kidney Outcome Quality Initiatives (KDOQI). They were managed at the RMC established at the Peking University Third Hospital, by a multidisciplinary team (nephrologists, nurses, and dietitians) who developed care plans, clinical pathways, and a multidimensional patient-education program.

RESULTS

The most frequent causes of CKD among these 1,000 patient were glomerulonephritis (35%), hypertensive nephrosclerosis (19%), chronic interstitial nephritis (13%), and diabetic nephropathy (11%). Six percent of the patients had stage 1 CKD, 27% stage 2, 33% stage 3, 20% stage 4, and 13% had stage 5. Five hundred and fifty-four were male and 446 were female; mean age was 55 +/- 18.9 years (range 18-92 years). Seven hundred and seventy patients (77%) had hypertension; 400 patients (40%) had body mass index (BMI) equal to or higher than 25 kg/m(2); 180 (18%) had overt cardiovascular disease; 726 (72.6%) had low-density lipoprotein (LDL)-cholesterol higher than 2.6 mmol/l; 440 patients (44%) had hyperuriemia; and 274 patients (27.4%) had anemia (hemoglobin <110 g/l). Although the team is multidisciplinary, management of the patients in the RMC is undertaken mainly by nephrologists, whereas nurses and dietitians still do not play an important role. There are no family doctors in China and nephrologists are responsible for management of these patients' kidney disease and related complications.

CONCLUSIONS

Our findings show that the prevalence of hypertension, diabetes mellitus, overweight. and hyperuricemia is high among Chinese CKD population. Nurses and dietitians do not yet play an important role in the present pattern of RMC. We believe that the present medical care model should be revised because it does not address the concerns of CKD patients and their need for lifestyle changes that would help them to cope with their chronic condition.

Enzymatic assays for creatinine: time for action

Accurate serum creatinine measurements in glomerular filtration rate estimation (eGFR) using equations are critical to ongoing global public health efforts to improve the diagnosis and treatment of chronic kidney disease. There is now an ongoing activity to promote worldwide standardization of methods to determine creatinine together with the introduction of a revised eGFR equation appropriate for use with standardized creatinine methods. Standardization of calibration, i.e., implementation of calibration traceability to high-order reference measurement procedures and reference materials, does not, however, correct for analytical interferences of field methods (non-specificity bias). To account for the sensitivity of alkaline picrate-based methods to non-creatinine chromogens, some manufacturers have adjusted the calibration to minimize the pseudo-creatinine contribution of plasma proteins, producing results more closely aligned to the reference method (isotope dilution-mass spectrometry), but this strategy makes an assumption that the non-creatinine chromogen interference is a constant among samples, which is an oversimplification. Thus, analytical non-specificity for substances found in individual patient samples can affect the accuracy of eGFR computed from serum creatinine values for any alkaline picrate method, including the so-called "compensated" Jaffé methods. The use of assays that are more specific for serum creatinine determination, such as those based on enzymatic reactions, may provide more reliable eGFR values. Supporting the choice of more specific assays by clinical laboratories represents one of the main tasks of our profession in order to achieve the ultimate clinical goal, which is to routinely report an accurate eGFR in all the pertinent clinical situations.

Screening for chronic kidney disease: where does Europe go?

This review discusses various screening approaches for chronic kidney disease that are used in Europe. The criterion for defining chronic kidney disease in the various programs differs but is frequently limited to estimated glomerular filtration rate, thus offering only data on chronic kidney disease stages 3 and higher; however, screening should not be limited to measuring only estimated glomerular filtration rate but should also include a measure of microalbuminuria, because this will offer identification of chronic kidney disease stages 1 and 2. Defining these earlier stages is of importance because the risk for developing end-stage renal disease that is associated with stages 1 and 2 is nearly equal to the risk that is associated with stage 3. Moreover, the risk for cardiovascular events in stages 1 and 2 is equal to that in stage 3. Various reports argue that costs of screening programs in general practitioner or outpatient offices are high and that they are cost-effective only for preventing end-stage renal disease when they are limited to target groups, such as patients with diabetes or hypertension and elderly. The benefits of screening programs, however, should not be evaluated only with respect to the prevention of renal events but should also include the benefits of preventing cardiovascular events. The use of preselection based on either an impaired estimated glomerular filtration rate or on protein-dipstick positivity or elevated albuminuria in a morning urine void has been found effective in various European countries as an alternative for targeted screening.

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.

Outcomes in patients with chronic kidney disease referred late to nephrologists: a meta-analysis

PURPOSE

The study purpose was to compare differences in mortality and the duration of hospitalization in patients with chronic kidney disease who are referred early versus late to nephrologists.

METHODS

We searched English-language literature from 1980 through December 2005, along with national conference proceedings, the Web of Science Citation Index, and reference lists of all included studies. Twenty-two studies with a total sample size of 12,749 met inclusion criteria.

RESULTS

There was significantly increased overall mortality in the late referral group as compared with the early referral group (relative risk 1.99; 95% confidence interval [CI], 1.66 to 2.39, P <.0001). The duration of hospital stay, at the time of initiation of renal replacement therapy, was greater in the late referred group by an average of 12 days (95% CI, 8.0 to 16.1, P=.0007). Significant heterogeneity was detected for both outcomes.

CONCLUSION

Timing of referral emerged to be a significant factor impacting homogeneity in the mortality outcome. Our results suggest significantly higher mortality and increased early hospitalization of chronic kidney disease subjects referred late to nephrologists as compared with earlier referred subjects.

In search of a rational approach to chronic kidney disease detection and management

Rates of incident end-stage renal disease persist above established goals, driving efforts for early identification of chronic kidney disease (CKD) to reduce progression. The detection of CKD using existing electronic data sources has been proposed as an efficient identification method; however, this method is not without potential challenges and limitations.

Metabolic risk factors associated with serum creatinine in a non-diabetic population

Insulin resistance, low HDL-cholesterol and microalbuminuria are important components of the metabolic syndrome as defined by WHO. Insulin resistance and low HDL-cholesterol are also common in chronic kidney disease (CKD), but it is not clear whether they are early or late phenomenons in the development of renal failure. This study examined whether low-grade albuminuria (microalbuminuria), lipoprotein fractions, and the insulin/glucose ratio (IGR)-a surrogate marker of insulin resistance-were related to renal function (expressed as serum creatinine) in persons without diabetes and with apparently normal renal function. The study included 4,131 men and women aged 55-75 years from the cross-sectional Tromsø IV survey (1994-1995). Lifestyle factors, waist circumference and blood pressure were included in the analyses. Gender stratified multivariate analysis was used to assess the relationship between serum creatinine and microalbuminuria, lipoprotein fractions and IGR. Serum creatinine was positively associated with microalbuminuria in men (beta = 2.50, 95% confidence interval (CI) 0.66-4.34), but not in women. HDL-cholesterol and IGR were strongly associated with creatinine in both genders (HDL-cholesterol: Men: beta = -4.82, 95% CI -6.27 to -3.37; women: beta = -2.12, 95% CI -3.28 to -0.96. IGR: Second, third and fourth quartile compared with first quartile, men: beta = 0.94, 95% CI -0.63 to 2.51; 2.10, 95% CI 0.52-3.69 and 2.40, 95% CI 0.75-4.04; women: beta = 1.91, 95% CI 0.59-3.22; 2.61, 95% CI 1.28-3.95 and 3.20, 95% CI 1.80-4.60). These findings suggest that even early impairment of renal function may be associated with insulin resistance and dyslipidemia, regardless of renal albumin leakage.

Reporting of estimated GFR in the primary care clinic

BACKGROUND

Because serum creatinine is an insensitive measure of kidney dysfunction, guidelines have advocated routine use of estimated glomerular filtration rate (eGFR) to identify patients with chronic kidney disease (CKD). Patients with early (stage 3) CKD remain undiagnosed in primary care clinics; therefore, we hypothesized that routine reporting of eGFR in outpatient clinics would improve the recognition and treatment of CKD.

METHODS

A retrospective review of primary care patients was undertaken at the Bronx Veterans Affairs Medical Center, Bronx, New York, before and after the institution of routine eGFR reporting. We evaluated the achievement of diagnostic and therapeutic treatment goals based on the Kidney Disease Outcomes Quality Initiative guidelines (documentation of CKD, urinalysis assessment, blood pressure < 130/80 mm Hg, and renin-angiotensin system blockade) for patients with stage 3 CKD during each period.

RESULTS

Overall, patients with diabetes with early-stage CKD achieved superior treatment rates than similar patients without diabetes. Routine reporting of eGFR improved the documentation and identification of CKD by almost 50%, although absolute improvement was modest. Use of renin-angiotensin system blockers improved minimally, as did blood pressure control. Patients with documented CKD achieved treatment goals more frequently than patients without documented CKD.

CONCLUSION

Routine reporting of eGFR alone modestly improved the identification of patients with CKD without a clinically significant effect on care. For Modification of Diet in Renal Disease Study calculation of eGFR reporting to effect improvements in CKD care, it will be necessary to pair eGFR reporting with provider education to identify these patients and treat them effectively.

Understanding estimated glomerular filtration rate: implications for identifying chronic kidney disease

PURPOSE OF REVIEW

Glomerular filtration rate (GFR) can be estimated using serum markers such as serum creatinine (SCr) or cystatin C. This review presents new insights into estimated GFR based on theory, validation studies, SCr assay standardization, cystatin C, and longitudinal comparison with measured GFR.

RECENT FINDINGS

The estimation of GFR by SCr differs in health and in chronic kidney disease (CKD) due to differences in GFR range and in creatinine production between these two populations. Among populations with normal baseline GFR, there is a more rapid decline in measured GFR than in SCr-based estimated GFR. While elevated SCr is specific for CKD, other disease processes may lead to elevated cystatin C. Validation is improved by refitting equation coefficients to compare populations, recognizing the asymmetry between estimated GFR and measured GFR, and using residual plots instead of Bland-Altman plots to assess bias.

SUMMARY

As a screening test, SCr should be interpreted as a marker of CKD probability in the context of the patient's clinical presentation. Measured GFR or creatinine clearance may be helpful in high-risk patients with normal SCr levels. GFR estimating equations should be reserved for patients with identified CKD. Standardized SCr and cystatin C assays are needed.