[Secretion of beta-hCG in pregnancy: an artefact?]

The concentration of beta-subunit (hCG beta) cannot be exactly quantified by means of competitive immunoassay in the presence of high levels of hCG, e.g. during normal pregnancy. Although the specificity and sensitivity of immunometric assay with mixed monoclonal antibodies was much improved, false positive results of hCG beta can, however, be obtained, if a high concentration of hCG is present in the hCG beta-IRMA (Ozturk et al. 1987). In this study hCG beta was therefore measured by subtraction of the values obtained by 2 immunometric assays for hCG + hCG beta and hCG in 174 serum samples of normal pregnant women during the 4th and 20th week of pregnancy. As both values did not differ, no hCG beta activity could be confirmed. Serum samples from pregnant women or authentic substances (hCG and hCG beta) were analyzed qualitatively by means of gel filtration (Sephadex-G100 column) and measurement of hCG and hCG + hCG beta activity in the fractions. In the chromatograms of pregnant serum, only one fraction with a hCG activity was observed. No additional fraction corresponding to the hCG beta activity could be identified in these chromatograms. It is concluded that, the secretion of hCG beta in serum during pregnancy is very low (less than 1%) and that the hCG beta activity measured by means of radioimmunoassay may possibly be due to an artifact.