Serum levels of prostate-specific antigen and vitamin D in peritoneal dialysis patients

Measuring the free:total ratio of prostate-specific antigen (f/t-PSA) can improve the specificity of single-serum PSA values, distinguishing between benign prostatic hyperplasia (BPH) and prostatic carcinoma (PCa) in men over the age of 50. Additionally, clinical trials have shown that dihydroxyvitamin D3 can slow the rate of PSA rise in PCa patients. However, little is known regarding the applicability of those findings in men undergoing chronic peritoneal dialysis (CPD). In the present study, we investigated the prevalence of increased serum PSA levels among CPD patients and correlated those values with serum levels of vitamin D [25-hydroxyvitamin D3 and 1,25-dihydroxyvitamin D3]. We undertook a cross-sectional study of 71 male CPD patients without a known history of prostate cancer from 24 centers in Canada, Greece, and Turkey. All of the patients were more than 50 years of age. In these patients, we measured serum concentrations of PSA, free PSA (f-PSA), total PSA (t-PSA), prostate alkaline phosphatase (PAP), 25-hydroxyvitamin D3, 1,25-dihydroxyvitamin D3, and intact parathyroid hormone (iPTH). We recorded serum PSA levels < 4 ng/mL in 62 patients (87.3%, group A) and levels > 4 ng/mL in 9 patients (12.7%, group B). The f/t-PSA ratio was < 0.25 in 16 patients (22.5%). Group B patients were older than those in group A (median: 73 years vs. 65 years, p < 0.01) and had a lower body weight (median: 66.5 kg vs. 76.7 kg, p < 0.05). We observed no statistically significant difference between the two groups for serum 1,25-dihydroxyvitamin D3 (median: 9.8 ng/mL vs. 10.1 ng/mL) or 25-hydroxyvitamin D3 (8 ng/mL vs. 8.2 ng/mL) levels. Also, we observed no correlation between vitamin D levels and f/t-PSA, but iPTH levels were significantly higher in group A (200.5 pg/mL vs. 61.2 pg/mL, p < 0.04). Also, serum PAP levels correlated significantly with PSA (r = 0.49, p = 0.01) and with f-PSA (r = 0.56, p = 0.000). Our results showed no clear relationship between vitamin D and serum levels of PSA or-of f/t-PSA in PD patients. However, further studies are needed to better define the uses of these PSA markers in PD patients because, in such patients, other relevant factors might be implicated in their predictive value.