Enzyme-immunoassay of human placental lactogen

An enzyme-immunoassay (EIA) for estimation of human placental lactogen (HPL) in plasma or serum was developed using HPL labelled with horseradish peroxidase (HRP) and anti-HPL sera raised in rabbits. The separation between antiserum-bound and free labelled hormone was accomplished with a double antibody solid phase technique. Interference of substances from the sample with the immunoassay was prevented by dilution of the sample with at least a factor of 20 and measurement of the labelled hormone attached to the solid phase. The peroxidase activity was colorimetrically measured using o-phenyl-enediamine and urea peroxide as substrate. The standard curve of the assay ranged from 3 to 40 ng HPL/ml allowing estimations of HPL in serum or plasma starting from about the 10th week of pregnancy. Normal values were established. Intra- and inter-assay variation coefficients of 6 and 7.5% respectively were found. The EIA showed no cross-reaction with human serum proteins or HCG. The low cross-reaction noted with human growth hormone did not interfere with the assay. An excellent agreement was found with the results of radioimmunoassay (RAI).