Objective: To evaluate the clinical significance of serum alkaline phosphatase (ALP). ALP bone isoenzyme (ALPb) and prostate specific antigen (PSA) levels in predicting bony metastasis in prostatic carcinoma.
Patients and methods: The levels of serum ALP, ALPb and PSA were assessed in 32 patients with prostatic carcinoma and bony metastasis (group 1), 31 with prostatic carcinoma without bony metastasis (group 2), and 31 with benign prostatic hyperplasia (group 3). Bony metastases were detected using whole-body bone scintigraphy and ALPb was estimated electrophoretically before surgical or medical treatment. The levels of the three markers were compared for their ability to predict bony metastasis.
Results: In groups 1, 2 and 3, respectively, the mean (SD) serum levels of ALP were 304 (322.2), 76.6 (47.5) and 63.8 (14.7) IU/L, of ALPb were 79.9 (76.9), 23.6 (9.9) and 25.3 (9.0) IU/L and of PSA were 478.1 (352.2), 46.9 (32.1) and 8.1 (1.8) ng/mL. The differences in serum ALP and ALPb between groups 1 and 2, and between groups 1 and 3 were significant (P < 0.05), but not those between groups 2 and 3. The positive predictive value (PPV) for bony metastasis in patients with prostatic carcinoma was 91.3% (21/23) and 100% (18/18) and the negative predictive value (NPV) was 71.8% (28/39) and 68.9% (31/45) for ALP and ALPb, respectively.
Conclusion: Both serum ALP and ALPb were increased significantly in patients with prostatic carcinoma with bony metastasis. The level of ALPb had a higher PPV and specificity for bony metastasis than had the level of ALP, but a lower NPV and sensitivity than ALP or PSA (at PSA levels > 20 ng/mL).