Reliability of the MDRD method for estimating glomerular filtration rate in relation to gender, body mass index and extracellular fluid volume.
BACKGROUND
The accuracy of estimating glomerular filtration rate from plasma creatinine (eGFR) has been questioned but it is unclear how much covert error in several reference methods that have been used has contributed to this perceived inaccuracy. The aim of the study was to evaluate eGFR in comparison with a second 'gold standard' to test the performance of the primary gold standard and to examine the influence of patient demographics (age, body mass index (BMI), extracellular fluid volume (ECV) and gender).


METHODS
Non-fasting multisample GFR and ECV were measured in 80 subjects simultaneously and independently with Cr-51-EDTA (GFR(EDTA)) and iohexol (GFR(iohexol)). Percentage bias and imprecision in the prediction of, and disagreement with, GFR(EDTA) were compared between eGFR and GFR(iohexol). Another simplified method for measuring GFR, the slope-only method ((SO)GFR), was also evaluated against multisample GFR (measured with the opposing indicator). Accuracies were assessed in all subjects and across age, BMI and ECV boundaries of 65 y, 29 kg m(-2) and 14 L.


RESULTS
eGFR was less precise than GFR(iohexol) (imprecisions of 22.3% and 12.9%; P < 0.01). The precision of (SO)GFR was intermediate between eGFR and GFR(iohexol). Both GFR(iohexol) and eGFR were less precise in the elderly, the obese and men, but minimally influenced by ECV. (SO)GFR was minimally influenced by subject demographics.


CONCLUSIONS
Although eGFR does not predict GFR (based on a primary gold standard) as accurately as a second gold standard, a significant component of its poor performance is the result of inaccuracy in the primary gold standard. (SO)GFR measured with Cr-51-EDTA is superior to eGFR.
Bird
N J
NJ
Department of Nuclear Medicine, Addenbrooke's Hospital, Cambridge, UK.
Peters
C
C
Michell
A R
AR
Peters
A M
AM
D000328:Adult; D000367:Age Factors; D000368:Aged; D015992:Body Mass Index; D002860:Chromium Radioisotopes; D003404:Creatinine / Q000097:blood*; D004435:Eating / Q000502:physiology; D045604:Extracellular Fluid / Q000502:physiology*; D005260:Female; D005919:Glomerular Filtration Rate / Q000502:physiology*; D006801:Humans; D007472:Iohexol; D008297:Male; D008875:Middle Aged; D012015:Reference Standards; D015203:Reproducibility of Results; D012737:Sex Factors; D013223:Statistics as Topic
D002860:Chromium Radioisotopes; D007472:Iohexol; D003404:Creatinine