Accuracy of a GFR estimating equation over time in people with a wide range of kidney function.
ABSTRACT Change in glomerular filtration rate (GFR) is important for clinical decision making. GFR estimates from serum creatinine level provide an unbiased but imprecise estimate of GFR at single time points. However, the accuracy of estimated GFR over time is not well known.
Longitudinal study of diagnostic test accuracy.
4 clinical trials with longitudinal measurements of GFR and serum creatinine on the same day, including individuals with and without kidney disease with a wide range of kidney function, diverse racial backgrounds, and varied clinical characteristics.
GFR estimated using the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation.
GFR measured using urinary clearance of (125)I-iothalamate.
Data included 19,735 GFR measurements in 3,531 participants during a mean follow-up of 2.6 years. Mean values at baseline for measured and estimated GFR and error (measured GFR - estimated GFR) were 73.1 (95% CI, 71.6 to 74.5), 72.7 (95% CI, 71.5 to 74.0), and 0.14 (95% CI, -0.35 to 0.63) mL/min/1.73 m(2), respectively. Mean rates of change in measured and estimated GFR and error were -2.3 (95% CI, -2.4 to -2.1), -2.2 (95% CI, -2.4 to -2.1), and -0.09 (95% CI, -0.24 to 0.05) mL/min/1.73 m(2) per year (P < 0.001, P < 0.001, and P = 0.2, respectively). Variability (ie, standard deviation) among participants in rate of change in measured GFR, estimated GFR, and error was 4.3, 3.4, and 3.3 mL/min/1.73 m(2) per year, respectively. Only 15% of participants had a rate of change in error >3 mL/min/1.73 m(2) per year, and only 2% had a rate of change in error >5% per year.
Participants' characteristics were not available over time.
The accuracy of GFR estimates did not change over time. Clinicians should interpret changes in estimated GFR over time as reflecting changes in measured GFR rather than changes in errors in the GFR estimates in most individuals.
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ABSTRACT: Glomerular filtration rate (GFR) is the best overall measure of kidney function. Reference GFR measurements (e.g. inulin clearance) are laborious. Estimation of GFR using equations based on endogenous filtration markers is simpler, cheaper and easy to apply in practice but suffers from limited accuracy and reproducibility. This review summarizes the recent studies comparing measured and estimated GFR in various populations and disease settings. We consider the utility of newer estimating equations based on standardized methodology, including those incorporating cystatin C. Equations proposed by the Chronic Kidney Disease-Epidemiology (CKD-EPI) Consortium slightly improve the accuracy of GFR estimation compared with those used formerly. The black ethnicity coefficient in the CKD-EPI equation may not be transferable across other black populations and the equations require further validation in other ethnic groups. All currently reported equations fall short of ideal. Incorporation of cystatin C into the CKD-EPI equation improves precision and offers hope of a GFR estimate that may not require ethnic adjustment. The ideal biomarker and equation to estimate GFR would provide reproducible and accurate results across the entire range of GFRs, populations and diseases. Newer GFR markers and equations are required to fulfil this holy grail of research.Current Opinion in Nephrology and Hypertension 03/2014; · 3.96 Impact Factor
- Kidney International 04/2014; 85(4):723-7. · 8.52 Impact Factor
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ABSTRACT: Uncertainty exists regarding the optimal method to estimate glomerular filtration rate (GFR) for disease detection and monitoring. Widely used GFR estimates have not been validated in British ethnic minority populations.Methods/design: Iohexol measured GFR will be the reference against which each estimating equation will be compared. The estimating equations will be based upon serum creatinine and/or cystatin C. The eGFR-C study has 5 components:1)A prospective longitudinal cohort study of 1300 adults with stage 3 chronic kidney disease followed for 3 years with reference (measured) GFR and test (estimated GFR [eGFR] and urinary albumin-to-creatinine ratio) measurements at baseline and 3 years. Test measurements will also be undertaken every 6 months. The study population will include a representative sample of south-Asians and African-Caribbeans. People with diabetes and proteinuria (ACR >=30 mg/mmol) will comprise 20-30% of the study cohort.2)A sub-study of patterns of disease progression of 375 people (125 each of Caucasian, Asian and African-Caribbean origin; in each case containing subjects at high and low risk of renal progression). Additional reference GFR measurements will be undertaken after 1 and 2 years to enable a model of disease progression and error to be built.3)A biological variability study to establish reference change values for reference and test measures.4)A modelling study of the performance of monitoring strategies on detecting progression, utilising estimates of accuracy, patterns of disease progression and estimates of measurement error from studies 1), 2) and 3).5)A comprehensive cost database for each diagnostic approach will be developed to enable cost-effectiveness modelling of the optimal strategy.The performance of the estimating equations will be evaluated by assessing bias, precision and accuracy. Data will be modelled as a linear function of time utilising all available (maximum 7) time points compared with the difference between baseline and final reference values. The percentage of participants demonstrating large error with the respective estimating equations will be compared. Predictive value of GFR estimates and albumin-to-creatinine ratio will be compared amongst subjects that do or do not show progressive kidney function decline. The eGFR-C study will provide evidence to inform the optimal GFR estimate to be used in clinical practice.Trial registration: ISRCTN42955626.BMC Nephrology 01/2014; 15(1):13. · 1.64 Impact Factor