Circulating levels of pregnancy zone protein: normal range and the influence of age and gender.

Serum levels of pregnancy zone protein (PZP) were measured in 506 apparently normal males and 329 normal non-pregnant females, the age range being 18 to 70 years. The estimations of PZP were performed by sensitive radio-rocket-line immunoelectrophoresis. The distribution of the data had a marked positive skew in both sexes which was reduced following logarithmic transformation. Serum concentrations in both men and women were found to increase significantly with advancing age. This increase and the mean concentrations were significantly higher in females.