Validation of the Virga GFR equation in a renal transplant population.
BACKGROUND
Virga and colleagues derived a glomerular filtration rate (GFR) equation which demonstrated a superior performance over Cockcroft-Gault (C-G) and modified diet in renal disease-isotope dilution mass spectrometry (MDRD-IDMS) formulas in chronic kidney disease (CKD) patients.


OBJECTIVE
To validate the performance of the Virga equation on 103 renal transplant patients.


METHODS
We compared the performances of the MDRD-IDMS, C-G and Virga equations using inulin clearance as a reference test. Error, accuracy, relative accuracy, precision, scatter, and coefficient of variance of each equation were tested.


RESULTS
The mean absolute percentage error in estimated GFR by the new equation was 39.8 +/- 36.34% (mean +/- SD). Relative accuracy at 10, 30 and 50% range were 18.44, 48.54 and 73.78%, respectively. It has a bias of 0.09 +/- 0.169 and a precision of 19.69. Inulin clearance (GFR) in stages 1-4 were 106.19 +/- 14.11, 71.17 +/- 7, 42.37 +/- 8.40 and 22.92 +/- 3.48 ml/min/1.73 m(2), respectively. Comparative statistics in the overall population and in patients with transplant CKD stage 3T showed that the MDRD-IDMS equation had better accuracy. The performance of MDRD-IDMS over the Virga equation was clearly superior for males. In patients with CKD stage 2T, the Virga equation showed superiority over MDRD-IDMS. In the overall and subpopulations, the Virga equation performed better than the C-G equation.


CONCLUSIONS
Among renal transplant patients, the results suggest that the best GFR estimate is probably obtained using the MDRD-IDMS equation in moderate kidney failure whilst the Virga formula was superior to MDRD-IDMS for patients with mild kidney failure. As in untransplanted patients, estimating GFR with the MDRD-IDMS equation is not advisable in the range of normal renal function because of its known underestimation of renal function.
Zahran
Ahmed
A
Internal Medicine Department, Menoufiya University Hospital, Menoufiya University, Menoufiya, Egypt.
Hossain
Mohammad Akhtar
MA
Kora
Mahmoud Abd Elaziz
MA
Galal
Ali Zaki
AZ
Shoker
Ahmed
A
D000293:Adolescent; D000328:Adult; D000368:Aged; D003404:Creatinine / Q000097:blood; D005260:Female; D005919:Glomerular Filtration Rate / Q000502:physiology*; D006801:Humans; D007674:Kidney Diseases / Q000097:blood / Q000503:physiopathology / Q000601:surgery; D016030:Kidney Transplantation / Q000592:standards* / Q000639:trends; D008297:Male; D008657:Metabolic Clearance Rate / Q000502:physiology; D008875:Middle Aged; D008962:Models, Theoretical
D003404:Creatinine