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Comparative study of total prostate specific antigen and free to total prostate specific antigen ratio in the diagnosis of prostate cancer.

This descriptive study was done to compare total Prostate Specific Antigen (tPSA) and the Free to Total Prostate Specific Antigen [(F/T) PSA] ratio measurements for prostate cancer detection. This study included a total of 43 patients with suspected prostate cancer observed over a period of 12 months. Out of 43 consecutive male patients (mean age 69±9.39 years, range 48-100 years), 32 had benign disease (74%) and 11 had prostate carcinoma patients (26%), who had histologically proven prostate cancer. The mean total PSA was 67.9 ng/ml and 12.4 ng/ml in patients with carcinoma prostate and nodular hyperplasia of prostate (NHP) respectively (p<0.05). The mean free PSA in carcinoma patients was 7.4±9.8 ng/ml and in NHP patients it was 2.3±4.1 ng/ml. The difference in mean free PSA concentration was significant (p<0.05). The free to total PSA ratio in two groups was significantly different (p<0.01) from each other. In carcinoma patients, mean F/T PSA ratio was 0.144±0.152 as compared 0.328±0.076 in patients with benign disease. The sensitivity and specificity of the test was calculated at different F/T PSA ratio cutoff. At 0.1 cut off value, sensitivity of the test was 64% and specificity was 84%. The positive predictive value (PPV) was 58% and negative predictive value (NPV) was 87%. From cutoff value of 0.12 to 0.16, sensitivity was increased from 64% to 91% but specificity was reduced from 84% to 59%. The PPV did not show much change and NPV was increased from 89% to 95%. Increasing the cut off value thereafter showed no change in sensitivity but specificity was further reduced to 41%. Therefore in this patient, F/T PSA ratio cut off of 0.15 was found to be the appropriate cutoff value. In 43 men who were biopsied, 11(26%) prostatic carcinoma were identified. Only one patient (9.1%) had F/T PSA ratio above 0.15 and diagnosed by biopsied. Out of 32 patients who were negative for malignancy, 13 patients had F/T PSA ratio more than 0.15 and 19 patients had F/T PSA ratio less than 0.15. The validity of tPSA and F/T PSA ratio in the diagnosis of prostate cancer was identified by calculating their sensitivity, specificity, PPV and NPV. In case of F/T PSA ratio the sensitivity was 91% and in conventional tPSA the sensitivity was 82%. Specificity was low in both the cases. But in tPSA the specificity was only 13% compare to 59% in F/T PSA. Positive predictive value (PPV) for tPSA was 25% and in F/T PSA it was 44%. Negative predictive value (NPV) for t PSA was 67% and for F/T PSA was 95% which was very high. The effectiveness of F/T PSA ratio at 0.15 cut off value with corresponding tPSA>10ng/ml shows sensitivity 83% in prostate cancer and 50% in NHP patient.