Correlation between the complex PSA/total PSA ratio and the free PSA/total PSA ratio, sensitivity and specificity of both markers for the diagnosis of prostate cancer

Abstract

Objective: To compare the behaviour of the PSAcomplex/PSAtotal percentage (PSAc%) against the PSA free/PSA total (PSAl%) and analyse both markers for their usefulness in diagnosing prostate cancer.

Material and methods: We measured total PSA (PSAt), free PSA (PSAl), complex PSA (PSAc), PSAl% and PSAc% levels in 158 patients. Of these, 98 (62%) were biopsied for presenting PSAt≥3 ng/dl and PSAl%<20, PSAt>10, suspicious rectal examination or suspicious ultrasound node. We performed linear regression and Passing-Bablok regression analyses. The ROC curves were calculated to study the sensitivity and specificity of PSAl% and PSAc% and were compared to each other. The prostate cancer diagnoses were analysed by PSAl% and PSAc% by applying the χ(2) test.

Results: The correlation coefficient (r) was good (0.7447, P<.0001), and the index of determination (r(2)) was 0,5. The result of the Passing-Bablok analysis was a slope of 1.658 (1.452 to 1.897) and an intersection of 2.044 (-0,936 to 5.393). The optimal cutoff for PSAl% (≤14.7854) showed a sensitivity of 89.29% [95% CI, 0,642-0,823] and a specificity of 54.29% (95% CI, 0,642-0,823). The optimal cutoff for PSAc% (>89.7796) had a sensitivity of 71.43% (95% CI, 0,616-0,802) and a specificity of 71.43% (95% CI, 0,616-0,802). There were no significant differences when comparing the areas under the curve of both markers (P=.59). The PPV of PSAl% was less than that of PSAc% (45.7% vs. 71%).

Conclusion: There was a good correlation between PSAl% and PSAc%. PSAc% has demonstrated greater specificity and efficacy than PSAl% in the diagnosis of prostate cancer.

Keywords: Antígeno prostático-específico; Diagnosis; Diagnóstico; Neoplasias prostáticas; Prostate-specific antigen; Prostatic neoplasms.