Measurements of serum
prostatic acid phosphatase concentrations (PAP) by radioimmunoassay (RIA) were compared with the conventional measurements of serum
acid phosphatase activities using p-
nitrophenylphosphate (
pNPP, tot.) and
magnesium thymolphthalein monophosphate (
TMP) as substrates and L(+)-
tartrate (
pNPP, tr.) as inhibitor in five
prostatic cancer patients before
therapy and in 13 during
therapy. Elevated serum
acid phosphatase activities were detected in 2, 2 and 3 of the 5 untreated patients when using
pNPP (tot.),
pNPP (tr.) and
TMP enzyme assays, respectively. RIA for PAP detected elevated concentrations of the
enzyme in 4 of these patients' sera. Three of the patients without
metastases and one patient with suspected
metastases had elevated concentrations of PAP by RIA. Serum
acid phosphatase isoenzyme 2, which is mainly of prostatic origin, was separated chromatographically from serum samples with increased
acid phosphatase activity. It represented 60--92% of the total activity, when
TMP was used as substrate. Significant correlations (beta less than 0.001) were observed between all conventional
enzyme activity measurements used and PAP by RIA within the whole patient group (n = 18), but no correlations existed within the patient group (p = 6) of high normal, or low abnormal serum PAP (2.7--6.6 micrograms/l). In addition, PAP measured by RIA better reflected the clinical state of the 13 patients under treatment than the conventional
enzyme assays investigated.