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.

Testing for chronic kidney disease: a position statement from the National Kidney Foundation

Chronic kidney disease (CKD) is common in the United States. The estimated prevalence of CKD in US adults was 11.7% +/- 0.8% in 2000, based on the National Health and Nutrition Examination Survey (NHANES). Global estimates for CKD prevalence are less certain, but recent studies in Europe, Australia, and China suggest a high prevalence. The most common risk factors for CKD include diabetes, hypertension, cardiovascular disease, a family history of CKD, and age greater than 60 years. Major outcomes of CKD include progression to kidney failure, development of complications of impaired kidney function, and increased risk for cardiovascular disease. CKD is usually silent until its late stages, thus many patients with CKD are detected only shortly before the onset of symptomatic kidney failure, when there are few opportunities to prevent adverse outcomes. Earlier detection allows for more time for evaluation and treatment but requires explicit testing strategies for asymptomatic individuals at increased risk. In the majority of patients, CKD can be detected with 2 simple tests: a urine test for the detection of proteinuria and a blood test to estimate the glomerular filtration rate (GFR). These 2 tests facilitate detection of CKD by all physicians by allowing for identification of CKD without first requiring determination of its cause. Understanding the strengths and limitations of CKD testing is critical for appropriate implementation of these recommendations. Application of CKD testing in national and international screening and surveillance programs could improve public health related to CKD.

Interactive effect of retinopathy and macroalbuminuria on all-cause mortality, cardiovascular and renal end points in Chinese patients with Type 2 diabetes mellitus

AIMS

To examine the effect of albuminuria and retinopathy on the risk of cardiovascular and renal events, and all-cause mortality in patients with Type 2 diabetes.

METHODS

A post-hoc analysis of 4416 Chinese patients without macrovascular complications at baseline (age 57.6 +/- 13.3 years). Glomerular filtration rate (eGFR) was estimated by the abbreviated Modification of Diet in Renal Disease Study Group Formula, further adjusted for Chinese ethnicity. Clinical end points were all-cause mortality, cardiovascular events (heart failure or angina, myocardial infarction, lower limb amputation, re-vascularization procedures and stroke) and renal end points (reduction in eGFR by more than 50% or eGFR < 15 ml/min/1.73 m2 or death as a result of renal causes or need for dialysis).

RESULTS

Compared with individuals without complications, subjects with retinopathy and macroalbuminuria had higher rates of cardiovascular events (14.1 vs. 2.4%), renal events (40.0 vs. 0.8%) and death (9.3 vs. 1.7%, P < 0.001). For composite event of death, cardiovascular and renal events, the presence of retinopathy, microalbuminuria alone, macroalbuminuria alone, retinopathy with microalbuminuria or retinopathy with macroalbuminuria increased the risk [hazard ratio (95% CI)] by 1.61 (1.05 to 2.47; P = 0.04), 1.93 (1.38 to 2.69; P < 0.001), 4.34 (3.02 to 6.22; P < 0.001), 2.59 [1.76 to 3.81; P < 0.001) and 6.83 (4.89 to 9.55; P < 0.001) fold, respectively. The relative excess risk as a result of interaction between retinopathy and macroalbuminuria was 15.31, implying biological interaction in the development of renal events.

CONCLUSIONS

In Chinese patients with Type 2 diabetes, retinopathy interacts with macroalbuminuria to increase the risk of composite cardio-renal events.

Metabolic syndrome and chronic kidney disease in a Chinese population aged 40 years and older

OBJECTIVE

To explore the relationship between metabolic syndrome and chronic kidney disease (CKD) in a study population from a developing country.

PARTICIPANTS AND METHODS

The prevalence of metabolic syndrome (as most recently defined by the International Diabetes Federation) and CKD (defined as an estimated glomerular filtration rate of < 60 mL/min per 1.73 m2 and/or albuminuria) was determined in 2310 study participants (age > or =40 years) from Beijing, China, between May 12 and December 7, 2004. The relationship between metabolic syndrome and CKD was then analyzed.

RESULTS

Participants with metabolic syndrome had a higher prevalence of CKD (15.4% vs 8.3%; P<.001) than those without the syndrome. As the number of metabolic syndrome traits increased, so did the prevalence of CKD. Strong unadjusted and adjusted associations were observed between metabolic syndrome and CKD. For participants without hypertension and diabetes, metabolic syndrome was also associated with CKD (odds ratio, 2.03; 95% confidence interval, 1.05-3.94).

CONCLUSIONS

In these 2310 Chinese study participants aged 40 years and older, metabolic syndrome was associated with CKD.

Association Between Carotid Artery Intima-Media Thickness and Early-Stage CKD in a Chinese Population

BACKGROUND

Increased carotid artery intima-media thickness (IMT) predicts future vascular events in the general population. However, the relationship between IMT and chronic kidney disease (CKD) seldom was tested in subjects with early-stage CKD.

STUDY DESIGN

Cross-sectional study.

SETTING & PARTICIPANTS

1,046 residents in 1 district of Beijing participated in the study.

OUTCOMES & MEASUREMENTS

Carotid artery IMT was measured by means of high-resolution B-mode ultrasonography. Estimated glomerular filtration rate (eGFR) was calculated using the modified Modification of Diet in Renal Disease Study equation based on data for Chinese patients with CKD. Albuminuria was evaluated by means of urinary albumin-creatinine ratio on a morning spot urine sample.

RESULTS

Compared with subjects with eGFR greater than 90 mL/min/1.73 m(2) (>1.50 mL/s/1.73 m(2)), subjects with eGFR of 60 to 89 mL/min/1.73 m(2) (1.00 to 1.49 mL/s/1.73 m(2)) and 30 to 59 mL/min/1.73 m(2) (0.50 to 0.99 mL/s/1.73 m(2)) had higher mean IMT (0.74 +/- 0.27 versus 0.82 +/- 0.30 versus 0.94 +/- 0.38 mm; P < 0.001). IMTs of subjects with albuminuria tended to be higher than the mean value (0.79 +/- 0.29 versus 0.93 +/- 0.38 mm; P < 0.001). eGFR and urinary albumin-creatinine ratio significantly correlated with IMT in univariable analysis, but not after adjusting for traditional cardiovascular disease risk factors.

LIMITATIONS

Selection bias and low prevalence of CKD might affect the strength of the study.

CONCLUSIONS

In this Chinese population older than 40 years, carotid artery IMT was significantly higher in subjects with early-stage CKD. The greater prevalence of cardiovascular disease risk factors in patients with CKD appeared to account for the higher carotid artery IMT.

Prevalence of chronic kidney disease (CKD) in the Japanese general population predicted by the MDRD equation modified by a Japanese coefficient

BACKGROUND

The number of patients with end-stage renal disease (ESRD) in Japan has continuously increased in the past three decades. In 2005, 36,063 patients whose average age was 66 years entered a new dialysis program. This large number of ESRD patients could be just the tip of the iceberg of an increasing number of patients with chronic kidney disease (CKD). However, to date, a nationwide epidemiological study has not been conducted yet to survey the CKD population.

METHODS

Data for 527,594 (male, 211,034; female, 316,560) participants were obtained from the general adult population aged over 20 years who received annual health check programs in 2000-2004, from seven different prefectures in Japan: Hokkaido, Fukushima, Ibaraki, Tokyo, Osaka, Fukuoka, and Okinawa prefectures. The glomerular filtration rate (GFR) for each participant was estimated from the serum creatinine values, using the abbreviated Modification of Diet in Renal Disease (MDRD) study equation modified by the Japanese coefficient.

RESULTS

The prevalences of CKD stage 3 in the study population, stratified by age groups of 20-29, 30-39, 40-49, 50-59, 60-69, 70-79, and 80-89 years, were 1.4%, 3.6%, 10.8%, 15.9%, 31.8%, 44.0%, and 59.1%, respectively, predicting 19.1 million patients with stage 3 CKD in the Japanese general adult population of 103.2 million in 2004. CKD stage 4 + 5 was predicted in 200,000 patients in the Japanese general adult population. Comorbidity of hypertension, diabetes, and proteinuria increased as the estimated GFR (eGFR) decreased. The prevalence of concurrent CKD was significantly higher in hypertensive and diabetic populations than in the study population overall when CKD was defined as being present with an eGFR of less than 40 ml/min per 1.73 m(2) instead of less than 60 ml/min per 1.73 m(2).

CONCLUSIONS

About 20% of the Japanese adult population (i.e., approximately 19 million people) are predicted to have stage 3 to 5 CKD, as defined by a GFR of less than 60 ml/min per 1.73 m(2).

Carotid intima media thickness predicts cardiovascular diseases in Chinese predialysis patients with chronic kidney disease

Patients with chronic kidney disease (CKD) have a high risk for cardiovascular disease. Ultrasound measurements of the intima media thickness (IMT) in the carotid arteries is a strong predictor for cardiovascular events in the general population and dialysis patients. However, it is unclear whether carotid IMT is useful for the prediction of cardiovascular events in predialysis patients with CKD. The prediction power of carotid ultrasonography for cardiovascular event, rate of renal function decline, and all-cause mortality was tested in a cohort of 203 Chinese patients with stages 3 to 4 CKD. The average IMT was 0.808 +/- 0.196 mm; 121 (59.6%) patients had atherosclerotic plaques visualized. IMT correlated with patient age (r = 0.373, P < 0.001), serum LDL level (r = 0.164, P = 0.021), Charlson's comorbidity score (r = 0.260, P < 0.001), and serum C-reactive protein (r = 0.279, P < 0.001). Carotid IMT was significantly higher in patients with diabetes than in those without diabetes (0.930 +/- 0.254 versus 0.794 +/- 0.184; P = 0.002). At 48 mo, the cardiovascular event-free survival was 94.4, 89.8, 77.7, and 65.9% for IMT quartiles I, II, III, and IV, respectively (log rank test, P = 0.006). By multivariate analysis with the Cox proportional hazard model, each higher quartile of IMT conferred 41.6% (95% confidence interval 6.4 to 88.4%; P = 0.017) excess hazard for developing cardiovascular event. The actuarial survival at 48 mo was 96.3, 98.0, 95.7, and 85.7% for IMT quartiles I, II, III and IV, respectively (log rank test, P = 0.127), and the difference was not statistically significant after Cox proportional hazard model to adjust for confounders. Carotid IMT did not correlate with the rate of renal function decline in these patients. Carotid IMT is a strong predictor of cardiovascular disease in Chinese predialysis patients and may be usefully applied for risk stratification in this group of patients.

Herbal Therapy Is Associated With the Risk of CKD in Adults Not Using Analgesics in Taiwan

BACKGROUND

Taiwan has the greatest incidence rate of end-stage renal disease in the world. Several cases of Chinese herb nephropathy were reported in Taiwan. Therefore, we studied the association between herbal therapy and chronic kidney disease (CKD) in Taiwan.

STUDY DESIGN

Cross-sectional survey.

SETTING & PARTICIPANTS

1,740 adults in the Nutrition and Health Survey in Taiwan (1993 to 1996).

PREDICTOR

Herbal and analgesic therapy.

OUTCOMES & MEASUREMENTS

CKD after adjustment for potential confounding variables.

RESULTS

Among medication users, prevalences of herbal therapy and analgesic use were 21.6% and 13.2%, respectively. The prevalence of CKD was 9.9%. Participants with CKD were older and had more analgesic use, diabetes, hypertension, and cardiovascular disease. Analgesic use was associated independently and positively with CKD (odds ratio, 2.2; 95% confidence interval, 1.4 to 3.5; P = 0.003) and CKD stage (odds ratio, 2.3; 95% confidence interval, 1.4 to 3.6; P = 0.003). Conversely, herbal therapy was associated independently and positively with CKD (odds ratio, 1.39; 95% confidence interval, 1.2 to 1.7; P = 0.002) and CKD stage (odds ratio, 1.38; 95% confidence interval, 1.1 to 1.7; P = 0.004) only in participants who did not use analgesics.

LIMITATIONS

Because this was a cross-sectional study, cause and effect could not be ascertained.

CONCLUSIONS

Herbal therapy was associated with CKD in adults in Taiwan who did not use analgesics.

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.

The usefulness of the International Diabetes Federation and the National Cholesterol Education Program's Adult Treatment Panel III definitions of the metabolic syndrome in predicting coronary heart disease in subjects with type 2 diabetes

OBJECTIVE

The purpose of this study was to compare the predictive value for coronary heart disease (CHD) of the International Diabetes Federation (IDF) definition (with Asian criteria for central obesity) of the metabolic syndrome with existing criteria of the National Cholesterol Education Program (NCEP) Adult Treatment Panel III (ATP III) in Chinese subjects with type 2 diabetes.

RESEARCH DESIGN AND METHODS

Subjects with type 2 diabetes and without macrovascular diseases or end-stage renal disease were categorized by the criteria of the IDF and the NCEP ATP III. CHD was defined as myocardial infarction, ischemic heart disease, coronary revascularization, heart failure, and death related to CHD.

RESULTS

Of 4,350 patients (aged 54.4 +/- 13.4 years; median follow-up period 7.1 [interquartile range 5.2-8.5] years), 65.9% had metabolic syndrome according to either IDF or NCEP ATP III criteria. The NCEP ATP III definition identified metabolic syndrome in 786 subjects (18.1%) who did not fulfill the criteria of the IDF. HDL cholesterol and systolic blood pressure were predictors of CHD after adjustment for other confounding factors. Compared with subjects without metabolic syndrome, the IDF criteria failed to predict CHD (hazard ratio 1.13 [95% CI 0.86-1.48], P = 0.374). In contrast, the NCEP ATP III definition (2.51 [1.80-3.50], P < 0.001) predicted an increased risk of CHD with the NCEP-only group having the highest risk (2.49 [1.66-3.73], P < 0.001).

CONCLUSIONS

With established type 2 diabetes, the IDF definition of the metabolic syndrome failed to identify a subgroup of patients who had the highest risk for CHD. Practitioners must recognize the appropriate setting for its application.

Estimation of glomerular filtration rate by the MDRD study equation modified for Japanese patients with chronic kidney disease

BACKGROUND

Accurate estimation of the glomerular filtration rate (GFR) is crucial for the detection of chronic kidney disease (CKD). In clinical practice, GFR is estimated from serum creatinine using the Modification of Diet in Renal Disease (MDRD) study equation or the Cockcroft-Gault (CG) equation instead of the time-consuming method of measured clearance for exogenous markers such as inulin. In the present study, the equations originally developed for a Caucasian population were tested in Japanese CKD patients, and modified with the Japanese coefficient determined by the data.

METHODS

The abbreviated MDRD study and CG equations were tested in 248 Japanese CKD patients and compared with measured inulin clearance (Cin) and estimated GFR (eGFR). The Japanese coefficient was determined by minimizing the sum of squared errors between eGFR and Cin. Serum creatinine values of the enzyme method in the present study were calibrated to values of the noncompensated Jaffé method by adding 0.207 mg/dl, because the original MDRD study equation was determined by the data for serum creatinine values measured by the noncompensated Jaffé method. The abbreviated MDRD study equation modified with the Japanese coefficient was validated in another set of 269 CKD patients.

RESULTS

There was a significant discrepancy between measured Cin and eGFR by the 1.0xMDRD or CG equations. The MDRD study equation modified with the Japanese coefficient (0.881xMDRD) determined for Japanese CKD patients yielded lower mean difference and higher accuracy for GFR estimation. In particular, in Cin 30-59 ml/min per 1.73 m(2), the mean difference was significantly smaller with the 0.881xMDRD equation than that with the 1.0xMDRD study equation (1.9 vs 7.9 ml/min per 1.73 m(2); P < 0.01), and the accuracy was significantly higher, with 60% vs 39% of the points deviating within 15%, and 97% vs 87% of points within 50%, respectively (both P < 0.01). Validation with the different data set showed the correlation between eGFR and Cin was better with the 0.881xMDRD equation than with the 1.0xMDRD study equation. In Cin less than 60 ml/min per 1.73 m(2), the accuracy was significantly higher, with 85% vs 69% of the points deviating within 50% (P < 0.01), respectively. The mean difference was also significantly smaller (P < 0.01). However, GFR values calculated by the 0.881xMDRD equation were still underestimated in the range of Cin over 60 ml/min per 1.73 m(2).

CONCLUSIONS

Although the Japanese coefficient improves the accuracy of GFR estimation of the original MDRD study equation, a new equation is needed for more accurate estimation of GFR in Japanese patients with CKD stages 3 and 4.

The relationship between serum creatinine and estimated glomerular filtration rate: implications for clinical practice

INTRODUCTION

A new classification of chronic kidney disease (CKD) has been widely adopted that stratifies patients into 5 'stages' according to estimated glomerular filtration rate (eGFR). In adults the most commonly used formulae to calculate eGFR are the Cockcroft and Gault (C and G) and Modification of Diet in Renal Disease (MDRD) formulae. The UK Renal Association has recommended calculation of MDRD eGFR to screen for reduced kidney function in primary and secondary care.

AIM

The aim of this study was to explore the implication of using these predictive formulae.

METHODS

We searched for patients currently attending a renal clinic who have ever had a serum creatinine (SCr) of exactly 100 micromol/L, 150 micromol/L or 200 micromol/L. The C and G and MDRD eGFRs corresponding to that SCr were calculated. The proportion of patients in each stage of the CKD classification was determined.

RESULTS

For a SCr of 100 micromol/L mean eGFR was 86.5 ml/min (range 31.0 - 192.8) by C and G and 63.8 ml/min (range 39.7 - 99.9) by MDRD (p < 0.0001; t-test of mean). For SCr 150 micromol/L mean eGFR was 51.7 ml/min (18.0 - 110.4) by C and G and 38.0 ml/min (20.7 - 54.8) by MDRD (p < 0.0001). For SCr of 200 micromol/L mean eGFR was 34.4 ml/min (12.6 - 89.5) by C and G and 27.3 ml/min (16.7 - 41.3) by MDRD (p < 0.0001). Using MDRD eGFR 46.5% patients with a SCr of 100 micromol/L have stage 3 CKD (GFR 30-60 ml/min) and all patients with a SCr of 150 micromol/L or 200 micromol/L have CKD 3 or worse. 8.6% of males with SCr 100 micromol/L had stage 3 CKD or worse compared with 86.8% females. 70.2% patients > 65 years old with SCr 100 micromol/L had stage 3 CKD.

CONCLUSIONS

Targeted screening of patients at-risk for CKD will identify a large number of patients who require management of CKD and potential referral to nephrology services even at levels of SCr regarded as 'normal' or mildly.

Bias and precision of estimated glomerular filtration rate in children

Determining true glomerular filtration rate (GFR) using an exogenous marker is time-consuming and cumbersome. Therefore, creatinine-based estimates of GFR are used. Recent papers using new population-specific/local parameters in their prediction equations, standardizing creatinine determination or adding other endogenous surrogate markers of GFR, like cystatin C, could demonstrate an improvement of bias inherent in the results of the prediction equations. Precision, however, is still poor. Currently, we have to accept a precision (as defined in the so-called Bland-Altman plot) of +/-20% in adults and +/-30-40% in children. This problem of poor precision/uncertainty is especially bothering in the higher, near normal GFR range. Caution should be exercised when applying prediction equations in individuals in need of an accurate GFR determination. In that case, a real clearance procedure has to be performed. In the long run, the true clearance procedure should be simplified using new exogenous GFR markers and developing new devices, allowing GFR measurements to be performed, for example, transcutaneously. Such a procedure would be more acceptable for both patients and physicians.

Changes in the Demographics and Prevalence of Chronic Kidney Disease in Okinawa, Japan (1993 to 2003)

To compare the risk factor demographics and the prevalence of chronic kidney disease (CKD), we analyzed two databases from the 1993 (N=143,948) and 2003 (N=154,019) mass screenings in Okinawa, Japan (Okinawa General Health Maintenance Association registry). We estimated the glomerular filtration rate (GFR) using serum creatinine (SCr) levels. SCr was measured by the modified Jaffe method in 1993 and by enzyme assay in 2003; the relation between the two methods was: SCr (Jaffe) = 0.194 + 1.079 x SCr (enzyme). CKD prevalence was compared using the estimated GFR calculated by the abbreviated Modification of Diet in Renal Disease (MDRD) equation. SCr was measured in 66.2% (1993) and 69.8% (2003) of the total screenees. Proteinuria was present in 3.4% (1993) and 4.3% (2003) of the total screened population, respectively. The prevalence of CKD (GFR<60 ml/min/1.73 m(2)) was similar between the two databases, being 15.7% in 1993 and 15.1% in 2003. However, the demographics of the CKD risk factors changed during the study period. The mean level of systolic blood pressure decreased, whereas the prevalence of obesity and the mean levels of serum cholesterol and fasting plasma glucose increased. In 2003, the estimated prevalence of metabolic syndrome in the general population of Japan calculated using the modified National Cholesterol Education Program (NCEP) criteria was 19.1%. The prevalence of CKD was significantly associated with that of metabolic syndrome: the age- and sex-adjusted odds ratio was 1.332 (95% confidence interval [CI], 1.277-1.389; p<0.0001). In conclusion, the demographics of the participants of the general screenings in Okinawa, Japan differed between the 1993 and 2003 screenings, but the prevalence of CKD seemed to be similar, or at least did not increase substantially, between the two databases.

High prevalence and low awareness of CKD in Taiwan: a study on the relationship between serum creatinine and awareness from a nationally representative survey

BACKGROUND

The burden of chronic kidney disease (CKD) is a global challenge. Empirical evidence of low CKD awareness rates in developed countries speaks for an urgent need to strengthen strategies for CKD identification and prevention. The aim of this study is to estimate the awareness rate of CKD in Taiwan to promote early detection of CKD in this country.

METHODS

Data from a nationally representative survey were used for analysis. The study included 6,001 subjects. The simplified Modification of Diet in Renal Disease equation was used to define glomerular filtration rate (GFR) and CKD stages according to criteria of the US National Kidney Foundation. Descriptive methods were used to analyze data.

RESULTS

The prevalence of CKD stages 3 to 5 in Taiwan is 6.9% (95% confidence interval, 4.4 to 9.4). Awareness rates for CKD in Taiwan are low: 8.0% for individuals with stage 3, 25.0% for those with stage 4, and 71.4% for those with stage 5. Awareness rate is related closely to serum creatinine level: those with creatinine levels greater than 1.6 mg/dL (>141 micromol/L) are more likely to be informed of having a kidney disease.

CONCLUSION

The high prevalence and low awareness of CKD in Taiwan explicitly show the need to advocate more strongly for CKD prevention and education for both physicians and the populace. Establishment of a mandated automatic GFR reporting system may be the first priority we need to accomplish in Taiwan to improve kidney well-being.

Kidney function estimating equations: where do we stand?

PURPOSE OF REVIEW

Estimation of the glomerular filtration rate (GFR) is central to the diagnosis, evaluation and management of chronic kidney disease. This review summarizes recent data on the performance of equations using serum creatinine to estimate the GFR, particularly the Modification of Diet in Renal Disease (MDRD) Study equation.

RECENT FINDINGS

During 2005 GFR estimation has received substantial attention with a focus on comparing the MDRD Study equation with the Cockcroft-Gault equation. Several large studies (n>500) have appeared. Most studies discuss creatinine calibration but few were able to standardize measurements. Studies that did calibrate the creatinine had improved performance. Overall, the MDRD Study equation performed well in populations with a low range of GFR and often outperformed the Cockcroft-Gault equation. Both equations have lower precision in high GFR populations, and the MDRD equation under-estimated the GFR in a number of studies. Efforts are underway to develop improved prediction equations by pooling data across many study populations.

SUMMARY

Equations for estimating the GFR from serum creatinine are useful for systematic staging of chronic kidney disease. The MDRD Study equation and systematic creatinine assay calibration improve the level of precision and accuracy in many settings. GFR estimates are less useful in the normal range of GFR, however, and are sensitive to the population under study.

End-stage renal disease risk equations for Hong Kong Chinese patients with type 2 diabetes: Hong Kong Diabetes Registry

AIMS/HYPOTHESIS

The objective of the study was to investigate risk factors and develop risk equations for end-stage renal disease (ESRD) in Chinese patients with type 2 diabetes.

SUBJECTS AND METHODS

A prospective cohort of 4,438 patients with type 2 diabetes mellitus and without ESRD (median observation period 2.9 years, interquartile range 1.6-4.1 years) was included in the analysis. The end-point (ESRD) was defined by: (1) death due to diabetes with renal manifestations or renal failure; (2) hospitalisation due to renal failure; (3) estimated GFR (eGFR) <15 ml min(-1) 1.73 m(-2). Cox proportional hazards regression was used to develop risk equations. The data were randomly and evenly divided into the training data for development of the risk equations and the test data for validation. The validation was performed using the area under the receiver operating characteristic curve (aROC), which takes into account follow-up time and censoring.

RESULTS

During the observation period, 159 patients or 12.45 per 1,000 person-years (95% CI 10.52-14.37 per 1,000 person-years) developed ESRD. Known duration of diabetes, systolic blood pressure, log(10) total cholesterol:HDL cholesterol ratio and retinopathy were significant predictors of ESRD. After further adjusting for eGFR, log(10) spot albumin:creatinine ratio (ACR) and haematocrit, only eGFR, haematocrit and log(10) ACR remained as independent predictors of ESRD. The risk equation derived from these three independent predictors had good discrimination, with an aROC of 0.97.

CONCLUSIONS/INTERPRETATION

Estimated GFR, haematocrit and ACR were independent predictors of ESRD and the derived risk equation performed well in Chinese patients with type 2 diabetes.

Paired kidney analysis of tacrolimus and cyclosporine microemulsion-based therapy in Chinese cadaveric renal transplant recipients

Few studies used paired kidneys for comparison between tacrolimus and cyclosporine in renal transplantation. Most of the published data used whole blood trough levels for drug monitoring. However, the use of limited sampling strategy and abbreviated formula to estimate the 12-h area under concentration-time curve (AUC(0-12)) allowed better prediction of drug exposure. Sixty-six first cadaveric renal transplant recipients receiving paired kidneys were randomized to receive either tacrolimus-based (n = 33) or cyclosporine microemulsion (Neoral)-based therapies (n = 33). Abbreviated AUC(0-12) was used for drug monitoring and dose titration. Mean follow-up duration was 2.8 +/- 2 years. The patient and graft survival were comparable. Fewer incidence of acute rejection was observed in tacrolimus group (15% vs. 27.3%) though the difference was not significant (P = 0.23). The absolute value and the rate of decline of creatinine clearance were both significantly better in tacrolimus-treated patients. Prevalence of hypertension, post-transplant diabetes mellitus, infection, and malignancy were similar in both groups. Prevalence of hypercholesterolemia (11/33 vs. 4/33) and gum hypertrophy (6/33 vs. 1/33) was more common in cyclosporine-treated patients (P = 0.04 in both parameters). This was the first prospective, randomized study with paired kidney analysis showing the renal function was significantly better in tacrolimus-treated patients than in cyclosporine-treated patients.

Validation of Creatinine-Based Estimates of GFR When Evaluating Risk Factors in Longitudinal Studies of Kidney Disease

Whereas much research has investigated equations for obtaining estimated GFR (eGFR) from serum creatinine in cross-sectional settings, little attention has been given to validating these equations as outcomes in longitudinal studies of chronic kidney disease. A common objective of chronic kidney disease studies is to identify risk factors for progression, characterized by slope (rate of change over time) or time to event (time until a designated decline in kidney function or ESRD). The relationships of 35 baseline factors with eGFR-based outcomes were compared with the relationships of the same factors with iothalamate GFR (iGFR)-based outcomes in the African American Study of Kidney Disease and Hypertension (AASK; n = 1094). With the use of the AASK equation to calculate eGFR, results were compared between time to halving of eGFR or ESRD and time to halving of iGFR or ESRD (with effect sizes expressed per 1 SD) and between eGFR and iGFR slopes starting 3 mo after randomization. The effects of the baseline factors were similar between the eGFR- and iGFR-based time-to-event outcomes (Pearson R = 0.99, concordance R = 0.98). Small but statistically significant differences (P < 0.05, without adjustment for multiple analyses) were observed for seven of the 35 factors. Agreement between eGFR and iGFR was somewhat weaker, although still relatively high for slope-based outcomes (Pearson R = 0.93, concordance R = 0.92). Effects of covariate adjustment for age, gender, baseline GFR, and urine proteinuria also were similar between the eGFR and iGFR outcomes. Sensitivity analyses including death in the composite time-to-event outcomes or using the Modification of Diet in Renal Disease equation instead of the AASK equation provided similar results. In conclusion, the data from the AASK provide tentative support for use of outcomes that are based on an established eGFR formula using serum creatinine as a surrogate for measured iGFR-based outcomes in analyses of risk factors for the progression of kidney disease.

Modified glomerular filtration rate estimating equation for Chinese patients with chronic kidney disease

The Modification of Diet in Renal Disease (MDRD) equations provide a rapid method of assessing GFR in patients with chronic kidney disease (CKD). However, previous research indicated that modification of these equations is necessary for application in Chinese patients with CKD. The objective of this study was to modify MDRD equations on the basis of the data from the Chinese CKD population and compare the diagnostic performance of the modified MDRD equations with that of the original MDRD equations across CKD stages in a multicenter, cross-sectional study of GFR estimation from plasma creatinine, demographic data, and clinical characteristics. A total of 684 adult patients with CKD, from nine geographic regions of China were selected. A random sample of 454 of these patients were included in the training sample set, and the remaining 230 patients were included in the testing sample set. With the use of the dual plasma sampling (99m)Tc-DTPA plasma clearance method as a reference for GFR measurement, the original MDRD equations were modified by two methods: First, by adding a racial factor for Chinese in the original MDRD equations, and, second, by applying multiple linear regression to the training sample and modifying the coefficient that is associated with each variable in the original MDRD equations and then validating in the testing sample and comparing it with the original MDRD equations. All modified MDRD equations showed significant performance improvement in bias, precision, and accuracy compared with the original MDRD equations, and the percentage of estimated GFR that did not deviate >30% from the reference GFR was >75%. The modified MDRD equations that were based on the Chinese patients with CKD offered significant advantages in different CKD stages and could be applied in clinical practice, at least in Chinese patients with CKD.

Using standardized serum creatinine values in the modification of diet in renal disease study equation for estimating glomerular filtration rate

BACKGROUND

Glomerular filtration rate (GFR) estimates facilitate detection of chronic kidney disease but require calibration of the serum creatinine assay to the laboratory that developed the equation. The 4-variable equation from the Modification of Diet in Renal Disease (MDRD) Study has been reexpressed for use with a standardized assay.

OBJECTIVE

To describe the performance of the revised 4-variable MDRD Study equation and compare it with the performance of the 6-variable MDRD Study and Cockcroft-Gault equations.

DESIGN

Comparison of estimated and measured GFR.

SETTING

15 clinical centers participating in a randomized, controlled trial.

PATIENTS

1628 patients with chronic kidney disease participating in the MDRD Study.

MEASUREMENTS

Serum creatinine levels were calibrated to an assay traceable to isotope-dilution mass spectrometry. Glomerular filtration rate was measured as urinary clearance of 125I-iothalamate.

RESULTS

Mean measured GFR was 39.8 mL/min per 1.73 m2 (SD, 21.2). Accuracy and precision of the revised 4-variable equation were similar to those of the original 6-variable equation and better than in the Cockcroft-Gault equation, even when the latter was corrected for bias, with 90%, 91%, 60%, and 83% of estimates within 30% of measured GFR, respectively. Differences between measured and estimated GFR were greater for all equations when the estimated GFR was 60 mL/min per 1.73 m2 or greater.

LIMITATIONS

The MDRD Study included few patients with a GFR greater than 90 mL/min per 1.73 m2. Equations were not compared in a separate study sample.

CONCLUSIONS

The 4-variable MDRD Study equation provides reasonably accurate GFR estimates in patients with chronic kidney disease and a measured GFR of less than 90 mL/min per 1.73 m2. By using the reexpressed MDRD Study equation with the standardized serum creatinine assay, clinical laboratories can report more accurate GFR estimates.

Cardiovascular Disease in Early Stages of Chronic Kidney Disease in a Chinese Population

Cardiovascular disease (CVD) is one of the most serious complications of kidney disease, yet studies of CVD in early stage of chronic kidney disease (CKD) in Asian patients are very limited. Therefore, this study determined the prevalence and the spectrum of CVD in individuals with early-stage CKD and compared them with data of individuals without CKD. Compared with individuals with estimated GFR (eGFR) >90 ml/min per 1.73 m2, the prevalence of myocardial infarction, stroke, and total CVD of individuals with eGFR 60 to 89 ml/min per 1.73 m2 was increased by 91.4, 71.7, and 67.6%, respectively. For individuals with eGFR 30 to 59 ml/min per 1.73 m2, the percentage was 105.2, 289.1, and 200.7%, respectively. For each eGFR category, stroke was more prevalent than myocardial infarction. Compared with individuals with eGFR >90 ml/min per 1.73 m2, participants with eGFR 60 to 89 and 30 to 59 ml/min per 1.73 m2 tended to have more cardiovascular risk factors, and there were strong unadjusted and adjusted associations between CVD with different stages of eGFR (eGFR >90 ml/min per 1.73 m2 as reference). This is the first report on the prevalence and the spectrum of CVD in early stages of CKD in a community-based Chinese population. The spectrum of CVD in this Chinese population is different from reports of Western countries. Individuals with subtle decreased renal function seem much more likely to have multiple cardiovascular risk factors and have higher prevalence of CVD than those without CKD.

Glucose control influences glomerular filtration rate and its prediction in diabetic subjects

OBJECTIVE

Hyperglycemia increases glomerular filtration rate (GFR), but the influence of HbA(1c) (A1C) on GFR and GFR's prediction by recommended equations remains to be determined.

RESEARCH DESIGN AND METHODS

In 193 diabetic patients, we searched for an association between A1C and isotopically measured GFR (51Cr-EDTA) and their predictions by the Cockcroft and Gault formula (CG) and the modification of diet in renal disease (MDRD) equation. Their accuracy for the diagnosis of moderate (GFR <60 ml/min per 1.73 m(2)) or severe (GFR <30 ml/min per 1.73 m(2)) renal failure was compared from receiver operating characteristic (ROC) curves, before and after categorizing the patients as well (A1C <or=8%) or poorly controlled.

RESULTS

The mean GFR was 57.0 +/- 34.8 ml/min per 1.73 m(2) and was well correlated with both estimations (CG r = 0.75, MDRD r = 0.83; P < 0.05). The areas under the ROC curves were higher with the MDRD (P < 0.05). A1C was correlated (P < 0.001) with the GFR (r = 0.29), MDRD (r = 0.38), CG (r = 0.26), and the absolute differences between the GFR and their CG but not MDRD estimations (r = 0.17, P < 0.05). Each +1% A1C was associated with +6.0 ml/min per 1.73 m(2) GFR (CG +5.6, MDRD +5.3). After separating well-controlled (n = 88, A1C 7.0 +/- 0.7%) and poorly controlled (n = 105, 9.6 +/- 1.3%) patients, the diagnostic accuracies were better (P < 0.05) for the MDRD, except for the diagnosis of moderate renal failure in well-controlled patients (NS).

CONCLUSIONS

GFR and its estimations correlate with A1C. Although the relations between GFR and its estimations were not affected by the degree of glucose control, the precision and diagnostic accuracy of the CG formula were diminished for A1C >8%. The MDRD equation was more accurate and robust in diabetic patients with impaired renal function.

New insights into the epidemiology of chronic kidney disease in US Asians and Pacific Islanders

PURPOSE OF REVIEW

In contrast to advances in our understanding of health disparities in other ethnic groups within the US, differential outcomes associated with chronic kidney disease among US Asians have gone largely unexamined. Until recently, risk estimates for chronic kidney disease outcomes among US Pacific Islanders were virtually unknown. This review highlights recent contributions to our understanding of chronic kidney disease outcomes in US Asians and Pacific Islanders.

RECENT FINDINGS

Asians in the US appear to have a higher risk of end-stage renal disease relative to US whites after accounting for baseline kidney disease and many of the known risk factors for end-stage renal disease. The origins of the discrepancy in risk for end-stage renal disease between US Asians and whites do not appear to be explained by the socioeconomic and comorbidity disparities paradigm present in the US black vs. white model. Mounting evidence suggests that US Asians and Pacific Islanders receive substantially less predialysis care and proportionally fewer kidney transplants compared with US whites. Paradoxically, these populations have equivalent or better survival on dialysis.

SUMMARY

These data highlight the need for studies to elucidate the mechanisms underlying the differential outcomes observed among US Asians and Pacific Islanders. Efforts to identify ethnicity-specific risk factors for kidney disease and interventions aimed at promoting predialysis care and kidney transplantation among US Asians and Pacific Islanders could substantially reduce morbidity, mortality, and costs.

Hypertension and kidney disease in Asia

PURPOSE OF REVIEW

Communicable diseases were traditionally the major cause of public health concern in Asian countries, most of which were less developed. With industrialization and associated lifestyle changes during the past few decades, however, noncommunicable diseases similar to those that affect Western societies have emerged in Asian countries. The purpose of the review was to examine recent evidence about the burden and factors associated with hypertension and chronic kidney disease (CKD) in Asian countries.

RECENT FINDINGS

Hypertension has become one of the leading causes of mortality in Asia. Although its prevalence continues to rise, it remains under-diagnosed and under-treated. CKD is becoming increasingly common mainly due to an increase in risk factors such as high blood pressure, diabetes, and obesity. Treatment of advanced CKD is overwhelmingly burdensome in a resource poor environment. Barriers to early detection of CKD in Asians include the fact that equations to estimate the glomerular filtration rate have not been validated in this population, and the uncertainty about appropriate glomerular filtration rate cutoff values to define CKD.

SUMMARY

Concerted efforts are needed to develop and implement cost-effective strategies for prevention and treatment of hypertension and CKD in Asian countries. More research is needed on these conditions in these populations.

Prevalence of decreased kidney function in Chinese adults aged 35 to 74 years

BACKGROUND

Chronic kidney disease (CKD) is a major public health burden in Western countries but little is known about its impact in developing countries. We estimated the prevalence and absolute burden of CKD in the general adult population in China.

METHODS

A cross-sectional survey was conducted in a nationally representative sample of 15,540 Chinese adults aged 35 to 74 years in 2000 and 2001. Serum creatinine was measured using the modified kinetic Jaffe reaction method at a central laboratory calibrated to the Cleveland Clinic Foundation laboratory. Glomerular filtration rate (GFR) was estimated using the simplified equation developed by the Modification of Diet in Renal Disease study. CKD was defined as an estimated GFR <60 mL/min/1.73m2.

RESULTS

Overall, the age-standardized prevalences of GFR 60 to 89, 30 to 59, and <30 mL/min/1.73m2 were 39.4%, 2.4%, and 0.14%, respectively, in Chinese adults aged 35 to 74 years. The overall prevalence of CKD (GFR <60 mL/min/1.73m2) was 2.53%, representing 11,966,653 persons (1.31% or 3,185,330 men and 3.82% or 8,781,323 women). The age-specific prevalence of CKD was 0.71%, 1.69%, 3.91%, and 8.14% among persons 35 to 44, 45 to 54, 55 to 64, and 65 to 74 years old, respectively. The age-standardized prevalence of CKD was similar in urban (2.60%) and rural (2.52%) residents but was higher in south China (3.05%) than in north China (1.78%) residents.

CONCLUSION

Although the prevalence of CKD in China was relatively low, the population absolute burden is substantial. These data warrant a national program aimed at detection, prevention, and treatment of CKD in China.

A simplified Cockcroft-Gault formula to improve the prediction of the glomerular filtration rate in diabetic patients

AIM

The National Kidney Foundation recommends stratification of renal failure into moderate (Glomerular Filtration Rate: GFR = 30-60 mL/min/1.73 m2), severe (15-30) or terminal (<15) using the Cockcroft-Gault (CG) or the Modification of Diet in Renal Disease (MDRD) equations. We studied the biases in these methods in an attempt to improve the standard CG (MCG) and devise a strategy for stratification.

METHODS

GFR was measured by 51Cr-EDTA clearance in 200 diabetic patients: 100 (Group 1: study of concordance) before 2003 and 100 thereafter (Group 2: validation of MCG). The CG was modified by replacing body weight by its mean value: 76.

RESULTS

In group 1, the recommended equations only correctly stratified 50 patients. The CG, not the MDRD, underestimated GFR if BMI was normal, and overestimated it in obese patients. In group 2, the MCG was well correlated with GFR and not biased by weight. Over the whole population, the MCG and MDRD were more accurate for the diagnosis of moderate and severe renal failure. The MDRD showed the lowest differences with GFR, except if GFR > 60, where the MCG performed better. All formulae overestimated low GFR, the MDRD also underestimated high GFR. The best stratification (147/200) was obtained using the MCG if creatininemia < 120 micromol/l and the MDRD if creatininemia > or =120 micromol/l.

CONCLUSION

The CG is biased by weight, the MCG corrects this. The more accurate MDRD cannot be used in all patients as it underestimates high GFR. The best stratification was obtained using the MCG at low and the MDRD at high creatininemia.

Efficacy and safety of benazepril for advanced chronic renal insufficiency

BACKGROUND

Angiotensin-converting-enzyme inhibitors provide renal protection in patients with mild-to-moderate renal insufficiency (serum creatinine level, 3.0 mg per deciliter or less). We assessed the efficacy and safety of benazepril in patients without diabetes who had advanced renal insufficiency.

METHODS

We enrolled 422 patients in a randomized, double-blind study. After an eight-week run-in period, 104 patients with serum creatinine levels of 1.5 to 3.0 mg per deciliter (group 1) received 20 mg of benazepril per day, whereas 224 patients with serum creatinine levels of 3.1 to 5.0 mg per deciliter (group 2) were randomly assigned to receive 20 mg of benazepril per day (112 patients) or placebo (112 patients) and then followed for a mean of 3.4 years. All patients received conventional antihypertensive therapy. The primary outcome was the composite of a doubling of the serum creatinine level, end-stage renal disease, or death. Secondary end points included changes in the level of proteinuria and the rate of progression of renal disease.

RESULTS

Of 102 patients in group 1, 22 (22 percent) reached the primary end point, as compared with 44 of 108 patients given benazepril in group 2 (41 percent) and 65 of 107 patients given placebo in group 2 (60 percent). As compared with placebo, benazepril was associated with a 43 percent reduction in the risk of the primary end point in group 2 (P=0.005). This benefit did not appear to be attributable to blood-pressure control. Benazepril therapy was associated with a 52 percent reduction in the level of proteinuria and a reduction of 23 percent in the rate of decline in renal function. The overall incidence of major adverse events in the benazepril and placebo subgroups of group 2 was similar.

CONCLUSIONS

Benazepril conferred substantial renal benefits in patients without diabetes who had advanced renal insufficiency. (ClinicalTrials.gov number, NCT00270426.)

Prevalence of chronic kidney disease in a middle and old-aged population of Beijing

BACKGROUND

Chronic kidney disease (CKD) was epidemic worldwide. The prevalence of CKD indicators, including proteinuria, hematuria/uninfectious leukocyturia and reduced GFR, was investigated in the middle and old-aged population of Beijing Shijingshan district.

METHODS

Subjects of 2310 aged > or =40 y were enrolled. Their health conditions were taken by questionnaires and physical check-ups. Spot urine albumin to creatinine ratio, spot urine dipstick and microscopy for urine red cell and leukocyte, and serum creatinine was determined. Using simplified Modification of Diet in Renal Disease Study equation estimated GFR assessed renal function. The associations between age, gender, diabetes mellitus, and hypertension, and indicators of kidney damage were examined.

RESULTS

Through the questionnaires, the history of diabetes mellitus, hypertension and CKD were found in 28%, 47.1% and 3.6% of subjects, respectively. Albuminuria was detected in 8.4% of subjects, hematuria and uninfectious leukocyturia in 0.7%, and reduced GFR in 4.9%. Approximately 12.9% had at least 1 indicator of CKD. The known rate of CKD in the studied population was 7.1%. Age, diabetes mellitus, hyper fasting blood glucose and hypertension were independently associated with albuminuria; age, gender, hyper uric acid and albuminuria with reduced GFR. When proteinuria and reduced GFR were determined using spot urine dipstick protein > or =25 mg/dl and serum creatinine > or =133 micromol/l, the prevalence of proteinuria and reduced GFR were 4.7% and 0.8%, respectively.

CONCLUSION

The prevalence of CKD is common in middle and old-aged population of Beijing, especially in the elderly, but the known rate was relatively low. These findings highlight the clinical and public health importance of CKD.

Chronic kidney disease: A European perspective

There is an exponential growth worldwide of patients with end-stage renal disease (ESRD). Prevalences, outcomes, and underlying causes of ESRD are relatively well documented through different organizations. It is, however, clear that a large part of the bad outcome of ESRD patients is due to deficient follow-up during the earlier chronic kidney disease (CKD) stages. Data on CKD, prevalence of the different stages, and the evolution to ESRD are rather scant, and available data are conflictive. This is at least partly due to the lack of an international standard for measurement of renal function. In addition, there is compiling evidence that presence of proteinuria, even with a normal renal function, predisposes to ESRD. Most authors now prefer the term "kidney injury" rather than "kidney failure" to indicate people at risk for evolution to ESRD or for complications of CKD. Detection of these patients at risk is important to implement measures to slow down progression of CKD and avoid secondary complications. As it is clear that most of these CKD patients die before they reach ESRD, it might be that by taking the necessary preventive measures, the number of ESRD patients might still further increase exponentially.

Screening techniques for detecting chronic kidney disease

PURPOSE OF REVIEW

As patients with impaired kidney function are at increased risk not only for progressive renal function loss, but also for cardiovascular disease, it is of importance to have accurate techniques to screen patients for the presence of an impaired kidney function.

RECENT FINDINGS

Glomerular filtration rate can in mass screenings best be evaluated using a formula based upon a serum creatinine measurement and anthropometric parameters. The Cockcroft-Gault and Modification of Diet in Renal Disease (MDRD) formulas are mostly used. Both are easy to use, but have their limitations. Interpreting the results of such glomerular filtration rate estimates requires a good knowledge of these limitations. Urinary albumin excretion can best be measured from 24 h urine collections. As these collections are difficult to perform, however, an early morning spot urine sample for the measurement of urinary albumin concentration can be applied as preselection for screening purposes.

SUMMARY

Mass screening for early kidney function impairment, expressed by an impaired glomerular filtration rate or elevated urinary albumin excretion, may help to detect patients at increased cardiac and renal risk. This can best be done using formulas to estimate glomerular filtration rate and by measuring urinary albumin loss.

Prediction of two-sample (99m)Tc-diethylene triamine pentaacetic acid plasma clearance from single-sample method

OBJECTIVES

To develop an equation to predict dual plasma sample method (DPSM) (99m)Tc-diethylene triamine pentaacetic acid ((99m)Tc-DTPA) plasma clearance from single plasma sample method (SPSM), and to clarify the condition in which DPSM can be substituted by SPSM in measurement of glomerular filtration rate (GFR).

METHODS

Patients with chronic kidney disease (CKD) were selected. Watson modified Christensen and Groth equation was used to calculate (99m)Tc-DTPA plasma clearance by SPSM (sGFR). The equation recommended by the Nephrourology Committee of the Society of Nuclear Medicine was used to calculate (99m)Tc-DTPA plasma clearance by DPSM (tGFR) in each patient. The difference between sGFR and tGFR was expressed as percent of the average of these two methods, and tGFR was predicted from sGFR. Plasma creatinine was measured by the kinetic picrate method, and GFR estimated by abbreviated modification of diet in renal disease (MDRD) equation (aGFR) and Cockcroft-Gault equation (cGFR) were evaluated as criteria in selection of DPSM and SPSM.

RESULTS

Three hundred and sixty-nine patients with CKD were selected (208 male and 161 female). The average age and body weight were 51.4 +/- 15.5 years and 67.2 +/- 12.5 kg, respectively. The causes of CKD were glomerular disease, renal arterial stenosis, chronic tubulointerstitial disease, and other causes or causes unknown. The average tGFR was 62.9 +/- 36.5 ml/min/1.73 m2, ranging from 1-180 ml/min/1.73 m2. sGFR was significantly correlated with tGFR (r = 0.9194, p < 0.001), but widely scattered when tGFR <30 ml/min/1.73 m2; in contrast, then tGFR was > or =30 ml/min/1.73 m2, the difference was constant (-1.1%, 95% confidence interval -18.3%, 16.1%), and tGFR could be predicted from sGFR using the equation: predicted tGFR (ml/min/1.73 m2) = 7.4244 + 0.7318 x sGFR + 0.0022 x sGFR2 (n = 299, r2 = 0.9428, p < 0.001), and the difference decreased to 0.1%, 95% confidence interval (-15.8%, 16.0%). aGFR was better than cGFR in diagnosis of tGFR <30 ml/min/1.73 m2, the diagnostic sensitivity of a cut off value of aGFR = 45 ml/min/1.73 m2 was 91.8%, and recommended as a criterion in the selection of DPSM and SPSM.

CONCLUSION

When GFR > or =30 ml/min/1.73 m2, tGFR can be predicted from sGFR, which will simplify the reference GFR measurement in clinical trials. sGFR becomes widely scattered when tGFR is less than 30 ml/min/1.73 m2. To obtain reliable reference GFR values, it is recommended that DPSM be used in clinical trials when aGFR is less than 45 ml/min/1.73 m2.

Welcome to the era of CKD and the eGFR

Estimating glomerular filtration rate using a simplified formula will lead to a vast increase in detection of chronic kidney disease in Australia.

Chronic kidney disease and automatic reporting of estimated glomerular filtration rate: a position statement

The systematic staging of chronic kidney disease (CKD) by glomerular filtration measurement and proteinuria has allowed the development of rational and appropriate management plans. One of the barriers to early detection of CKD is the lack of a precise, reliable and consistent measure of kidney function. The most common measure of kidney function is currently serum creatinine concentration. It varies with age, sex, muscle mass and diet, and interlaboratory variation between measurements is as high as 20%. The reference interval for serum creatinine concentration includes up to 25% of people (particularly thin, elderly women) who have an estimated glomerular filtration rate (eGFR) that is significantly reduced (< 60 mL/min/1.73 m2). The recent publication of a validated formula (MDRD) to estimate GFR from age, sex, race and serum creatinine concentration, without any requirement for measures of body mass, allows pathology laboratories to "automatically" generate eGFR from data already acquired. Automatic laboratory reporting of eGFR calculated from serum creatinine measurements would help to identify asymptomatic kidney dysfunction at an earlier stage. eGFR correlates well with complications of CKD and an increased risk of adverse outcomes such as cardiovascular morbidity and mortality. We recommend that pathology laboratories automatically report eGFR each time a serum creatinine test is ordered in adults. As the accuracy of eGFR is suboptimal in patients with normal or near-normal renal function, we recommend that calculated eGFRs above 60 mL/min/1.73 m2 be reported by laboratories as "> 60 mL/min/1.73 m2", rather than as a precise figure.

Performance of the Cockcroft-Gault and Modification of Diet in Renal Disease Equations in Estimating GFR in Ill Hospitalized Patients

BACKGROUND

Estimating glomerular filtration rate (GFR) in severely ill inpatients is clinically important for therapeutic interventions and prognosis, but notoriously difficult to do accurately. The Modification of Diet in Renal Disease (MDRD) equation and Cockcroft-Gault (CG) formula are widely used to estimate renal function in sick hospitalized patients; however, neither method has been validated in this setting.

METHODS

Iodine 125-iothalamate clearances (iGFR) performed in 107 sick inpatients with renal dysfunction were compared with estimated GFRs (eGFRs) from the 6- and 4-variable MDRD (MDRD eGFR) and CG (CG eGFR) equations.

RESULTS

Mean serum creatinine (SCr) level was 3.5 +/- 2.0 mg/dL (309 +/- 177 micromol/L), and mean iGFR was 17.1 +/- 17.9 mL/min/1.73 m2 (0.29 +/- 0.30 mL/s/1.73 m2). Six-variable MDRD eGFR was 22.5 +/- 17.4 mL/min/1.73 m2 (0.38 +/- 0.29 mL/s/1.73 m2), 4-variable MDRD eGFR was 23.9 +/- 16.3 mL/min/1.73 m2 (0.40 +/- 0.27 mL/s/1.73 m2), and CG eGFR was 26.0 +/- 17.1 mL/min/1.73 m2 (0.43 +/- 0.29 mL/s/1.73 m2). Blood urea nitrogen (BUN)/SCr ratios greater than 20 were seen in 58% of patients. Overall, the CG and MDRD equations overestimated iGFR, with poor agreement. Overestimation of at least 25% of measured iGFR was seen in 63%, 67%, and 70% of all inpatients when using the 6-variable MDRD, 4-variable MDRD, and CG equations, respectively. Accuracy of eGFR within 50% of measured iGFR was 55% for the 6-variable MDRD equation, 49% for the 4-variable MDRD equation, and 40% for the CG formula. The performance of both methods deteriorated further in patients with a BUN/SCr ratio greater than 20.

CONCLUSION

Estimation equations are performed poorly compared with iGFR and are not reliable measures of actual level of function in sick hospitalized patients, especially those with a high BUN/SCr ratio. Although use of the 6-variable MDRD equation provides a better estimation of GFR, it still is unsuitable for clinical application in this population.