Background and objectives: GFR is scaled to body surface area (S), whereas hemodialysis dosage is scaled to total body water (V). Scaling to metabolic rate (M) or liver size (L) has also been proposed.
Design, setting, participants, & measurements: In 1551 potential kidney donors (662 men and 889 women) for whom GFR had been estimated from (125)I-iothalamate clearance (iGFR) between the years 1973 and 2005, iGFR scaling was examined. Scaling was to estimates of S, V, M, or L. The study looked at the variation of iGFR by gender, age, S, V, M, and L within the study population.
Results: In multiple regression analysis, neither gender nor race was significantly associated with iGFR after controlling for height, weight, and age. Raw iGFR averaged 122 +/- 23 ml/min in men and 106 +/- 21 ml/min in women (P < 0.001). In an adjusted analysis, iGFR scaled to S or L was similar for men and women (NS), whereas iGFR scaled to either V or M was substantially different between the genders (P < 0.001). When the patients by gender were divided into five quintiles of V or S, the iGFR-V ratio varied more with body size than iGFR scaled to the other measures.
Conclusions: iGFR scaled to S or L was similar in men and women. Scaling to either M or V resulted in a sizeable gender difference, whereas scaling to V led to markedly different values of iGFR across body size.