Prediction of Glomerular Filtration Rate From Body Cell Mass and Plasma Creatinine

Abstract

The gold standards for the measurement of glomerular filtration rate (GFR) are inulin clearance and radioisotopic methods. However, creatinine clearance is the most used test to evaluate GFR in clinical practice. Its adequacy is questionable, since its repeatability is quite poor, mainly due to errors in the collection of urine. The aim of this study was to evaluate a new method to predict GFR from the body cell mass (BCM) and plasma creatinine (Pcr), avoiding urine collection. The values of BCM were obtained in 275 adult renal patients with different renal function, ranging from normality to advanced renal failure. The relationship of GFR (clearance of (99m)Tc-DTPA) with BCM and Pcr was calculated in the first 85 patients. A highly significant linear correlation was found between GFR and the ratio BCM/Pcr. Thereafter, GFR was predicted from BCM and Pcr (BCM GFR) with formulas derived from the relationships found between GFR and the ratio BCM/Pcr. For comparison, GFR was predicted also according to other prediction formulas: Cockcroft and Gault (CG GFR), and the simplified MDRD formula (MDRD GFR). BCM GFR gave a more precise estimate of GFR than CG GFR and MDRD GFR. In fact, BCM GFR had the best correlation and agreement with true GFR ((99m)Tc-DTPA). Furthermore, CG GFR and MDRD GFR markedly overestimated true GFR. Finally, the error of prediction of BCM GFR was definitely lower than that of the two other estimates of GFR. GFR can be predicted from BCM and plasma creatinine. This method, which is very simple and accurate, seems suitable to establish the adequate dosage of drugs cleared by the kidneys.

Performance of the Cockcroft-Gault, MDRD, and New CKD-EPI Formulas in Relation to GFR, Age, and Body Size

“…This makes it more likely that the accuracy of MDRD and CKD-EPI are indeed highly in line with each other; however, in the elderly and in those with a low body weight or BMI, Cockcroft-Gault remains a good alternative. Our finding that the MDRD or the CKD-EPI formula seems to be the best option for young patients is in agreement with the results of Donadio et al (5). Using these formulas in the elderly is also supported by others (8,21), although not by all (5,22).…”

“…Our finding that the MDRD or the CKD-EPI formula seems to be the best option for young patients is in agreement with the results of Donadio et al (5). Using these formulas in the elderly is also supported by others (8,21), although not by all (5,22). This difference might be caused by small differences in bias and precision between the formulas in the elderly, because all formulas had smaller absolute biases in these subjects.…”

“…In line with our results, others also found the estimation of Cockcroft-Gault to be more dependent on body weight or BMI than MDRD (8,19,20). The influence of BMI on the bias of Cockcroft-Gault has been described before (5,23), although not all studies found this relationship (6,21).…”

“…This difference might be caused by small differences in bias and precision between the formulas in the elderly, because all formulas had smaller absolute biases in these subjects. For Cockcroft-Gault, a relation between its bias and age has been shown before (5,8,22).…”

Exogenous Fluorescent Agents for the Determination of Glomerular Filtration Rate

“…[16][17][18] The results from this analysis are frequently misleading since the value is affected by age, state of hydration, renal perfusion, muscle mass, dietary intake, and many other anthropometric and clinical variables. Theoretical methods for estimating GFR (eGFR) [19][20][21] from body cell mass and plasma creatinine concentration have also been developed, but these methods also rely on the above anthropomorphic variables. Moreover, creatinine is www.intechopen.com partially cleared by tubular secretion along with glomerular filtration, and, as Diskin 17 recently remarked, "Creatinine clearance is not and has never been synonymous with GFR, and all of the regression analysis will not make it so because the serum creatinine depends upon many factors other than filtration."…”