Stability of free and total prostate specific antigen in serum from patients with prostate carcinoma and benign hyperplasia
Abstract
Instability of prostate specific antigen (PSA) in serum might complicate the interpretation of the free-to-total PSA ratio. We studied the in vitro stability of free PSA and total PSA in serum of patients with prostate cancer or benign prostate hyperplasia (BPH), and of elderly men without known prostate disease. Furthermore, we investigated conditions to stabilize the in vitro values in serum. The effects of storage at 4C on free and total PSA were investigated in serum of 32 men with prostate cancer, 25 with BPH and 29 older than 70 years. All had total PSA less than 25 microg./l. The influence of total PSA levels on in vitro changes in free-to-total PSA was studied in serum of 39 other prostate cancer patients (total PSA 1.7 to 298 microg./l.). Stabilization studies were performed in yet another series of samples from 54 prostate cancer patients (total PSA 1.3 to 238 microg./l.) by adjustment of serum pH to 5.5 before storage. Free and total PSA was measured by a commercial immunofluorometric assay, as well as by in-house immunofluorometric assays. Statistical analyses of the results were performed by analysis of variance with repeated measures. We found no difference between the results obtained by the 2 assay systems. Afte...Continue Reading