Plasma leptin measurements in epidemiological investigation: comparison of two commonly used assays and estimate of regression dilution bias
Iacone, R.; Russo, O.; Russo, P.; Venezia, A.; Varriale, V.; Gerardi, M.C.; Strazzullo, P.
Nutrition Metabolism and Cardiovascular Diseases Nmcd 12(2): 71-79
2002
ISSN/ISBN: 0939-4753 PMID: 12189906 Document Number: 548232
Background and aim: As leptin is the object of intensive clinical research, we compared the radioimmunological assay (RIA) and ELISA commercially available for measuring its plasma concentration in humans (Study 1), and sought to determine the power of a single plasma leptin measurement to characterize adequately a subject within a population on the basis of its intra- and inter-individual variations (Study 2). Methods and results: In study 1, plasma leptin concentrations were determined by means of RIA and ELISA in a sample of 80 males. The measurements obtained using the two methods were closely correlated (r=0.942), but the bias of the means was 21.1+or-73.5% (M+or-SD, p<0.001) and indicated that the two assays were not in agreement with each other. As expected, there were strong statistical associations between plasma leptin and a number of anthropometric indices, but the slopes of the regression of leptin concentration was significantly steeper when measured by ELISA. In study 2, ELISA was used to measure plasma leptin concentrations in three different samples obtained from 12 males and 12 females at two-week intervals. The inter-individual variation in plasma leptin was much greater than its intra-individual variation (the ratio of intra- to inter-individual variance=0.05 and 0.04 in males and females, respectively), thus suggesting that a single fasting measurement is sufficient to characterise an individual's plasma leptin level within a population. Conclusions: ELISA is at least as effective as RIA in measuring plasma leptin, and is fully suitable for epidemiological investigations. A single measurement made in the morning and under fasting conditions is sufficient to characterise an individual within a population.