Plasma leptin concentrations in lean and obese human subjects and Prader-Willi syndrome: Comparison of RIA and ELISA methods

Immunoassays for circulating leptin are important research tools for examin ing the role and regulation of leptin expression in human obesity. However, uncertainty exists regarding the comparability between studies of reported plasma or serum leptin concentrations. The purpose of the present study wa s to directly compare plasma leptin concentrations by using two of the most widely reported immunoassay methods-namely, a commercially available radio immunoassay (RIA) and a proprietary enzyme-linked immunosorbent assay (ELIS A). Plasma leptin concentrations were measured in healthy lean and obese vo lunteers and in patients with Prader-Willi syndrome (PWS), Over a wide rang e of plasma concentrations (2 to 70 ng/mL), leptin measurements obtained wi th the RIA and ELISA methods were highly correlated (r = 0.957, P < .0001) and were essentially indistinguishable. Leptin levels measured by RIA and E LISA were highly correlated with body mass index (BMI) overall (r = 0.784, P < .0001 and r = 0.732, P < .0001, respectively) and in the lean and obese subgroups. When compared with the results in the lean individuals (mean +/ - SEM, 11.6 +/- 3.2 ng/mL), plasma leptin was significantly higher in both the obese (35.5 +/- 4.0 ng/mL, P < .0001) and the PWS subjects (30.7 +/- 6. 9 ng/mL, P < .05). However, after we controlled for differences in BMI, the leptin levels were similar in all three groups. In conclusion, we found th at the RIA and ELISA used in the present study yield plasma leptin concentr ations that are essentially indistinguishable. Our findings should facilita te comparisons of leptin levels measured by these two widely used immunoass ays in previous and future studies that examine the role of leptin in body weight regulation.