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Published on: May 10, 2013
Using standardized serum creatinine values in the modification of diet in renal disease study equation for estimating
Andrew S Levey1, Josef Coresh, Tom Greene
1Tufts-New England Medical Center, Boston, Massachusetts 02111, USA.
Insights
The revised 4-variable Modification of Diet in Renal Disease (MDRD) Study equation offers accurate glomerular filtration rate (GFR) estimates for chronic kidney disease patients with GFR below 90 mL/min/1.73 m2. This allows clinical labs to report improved GFR measurements.
Area of Science:
- Nephrology
- Clinical Chemistry
Background:
- Glomerular filtration rate (GFR) estimation is crucial for detecting chronic kidney disease (CKD).
- Accurate GFR estimation requires calibration of serum creatinine assays to the equation's developing laboratory.
- The 4-variable Modification of Diet in Renal Disease (MDRD) Study equation was reexpressed for a standardized assay.
Purpose of the Study:
- To evaluate the performance of the revised 4-variable MDRD Study equation.
- To compare the revised 4-variable MDRD equation with the 6-variable MDRD and Cockcroft-Gault equations.
Main Methods:
- A comparison of estimated GFR (eGFR) and measured GFR (mGFR) was conducted.
- Data from 1628 CKD patients across 15 clinical centers in the MDRD Study were analyzed.
- Serum creatinine was calibrated to an isotope-dilution mass spectrometry-traceable assay; mGFR was measured using 125I-iothalamate urinary clearance.
Main Results:
- The revised 4-variable MDRD equation demonstrated accuracy and precision comparable to the 6-variable MDRD equation.
- The revised 4-variable MDRD equation outperformed the Cockcroft-Gault equation, even when bias-corrected (90% vs. 60% within 30% of mGFR).
- All equations showed greater discrepancies at eGFR levels of 60 mL/min/1.73 m2 or higher.
Conclusions:
- The reexpressed 4-variable MDRD Study equation provides reliable GFR estimates for CKD patients with mGFR < 90 mL/min/1.73 m2.
- Use of the reexpressed MDRD equation with a standardized assay enables clinical laboratories to report more accurate GFR.
- Limitations include limited patient data with GFR > 90 mL/min/1.73 m2 and lack of comparison in a separate sample.
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.
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