Placental-type alkaline phosphatase in pregnancy and malignancy plasma: specific estimation using a monoclonal antibody in a solid phase enzyme immunoassay.

A solid-phase enzyme immunoassay has been developed using a monoclonal antibody with specificity only for the placental-type alkaline phosphatase isoenzyme (Pl-ALP). This assay is uniquely sensitive, having a lower limit of detection of 0.1 U/l (approximately 0.07 micrograms/l) Pl-ALP. All plasma samples from healthy non-pregnant individuals had undetectable Pl-ALP levels whereas, in pregnancy, a wide range (0-400 U/l) of Pl-ALP levels was noted for 208 maternal plasma samples from 12 weeks gestation to term. There was no significant difference in circulating Pl-ALP levels between severe pre-eclamptic and normal pregnancy. Low levels of Pl-ALP (0.1-4.7 U/l) were found in 31 of 217 plasmas from human malignancies. Within these, 23 of 65 (35%) histologically-proven ovarian carcinoma patients were positive.