One-step enzyme-linked immunosorbent assay (ELISA) for measurement of serum free leptin

In man, circulating leptin levels are increased with obesity and are regulated by a complex of hormonal, feeding and body-weight changes. Accurate and precise methods to quantitate circulating serum free leptin (f-leptin) concentrations are needed for physiological and clinical studies. We developed a one-step enzyme immunoassay to measure human f-leptin in serum. The detection limit was 0.40 ng/ml. The recovery of leptin added to serum was 90.8-102.8%. The within-run and between-day coefficients of variation (C.V.) ranged from 2.8 to 7.7 and 5.7 to 9.7%, respectively, and the immunoassay had an overall recovery rate for serial dilution in the range of 94. 0-109.9%. Measured serum f-leptin concentrations in 201 adults correlated (r=0.449, P<0.001) directly with body mass index (BMI kg/m(2)), particularly when results were separated by gender (r=0. 709 for male, P<0.001; r=0.643 for female, P<0.001). We conclude that this one-step enzyme immunoassay is accurate for measuring f-leptin in human serum.