A clinical assay for prostatic acid phosphatase using choline phosphate as a substrate: comparison with thymolphthalein phosphate.

We describe an assay method using choline O-phosphate as a substrate for the measurement of serum prostatic acid phosphatase as an aid in the diagnosis of prostatic cancer. Choline phosphate is hydrolyzed by homogeneous prostatic acid phosphatase, and it is also hydrolyzed by an acid phosphatase present in the serum of prostatic carcinoma patients. In contrast, serum samples from apparently healthy persons do not exhibit any significant choline O-phosphate phosphatase activity. There is a correlation of 98% (n = 46) between choline O-phosphate phosphatase activity and typical measurement for prostatic acid phosphatase activity carried out using thymolphthalein monophosphate as the substrate. The new method appears to be as accurate as colorimetric methods based on thymolphthalein phosphate as a substrate. Although not as sensitive as immunologically based methods, the present technique for measuring prostatic acid phosphatase activity using choline phosphate as a substrate is economical and relatively simple.