Variations in prostate-specific antigen free/total ratio in acute stress

Serum prostate-specific antigen complexed to alpha2-macroglobulin is occult and is not detected by conventional immunoassays. Conditions affecting alpha2-macroglobulin levels may alter the specificity of prostate-specific antigen free/total ratio in predicting prostate cancer. A group of patients (n=24) undergoing surgical stress due to a coronary artery bypass grafting was followed pre- and postoperatively up to 6 days. Total and free prostate-specific antigen, alpha2-macroglobulin, and C-reactive protein were measured by electrochemiluminescence, immunonephelometry, and immunoturbidimetry, respectively. Total prostate-specific antigen and C-reactive protein increased significantly postsurgery and remained elevated. Free/total ratio correlated negatively with C-reactive protein only (p = 0.000) using xtgee panel data analysis, after correction for plasma volume changes using albumin. Increased C-reactive protein may reflect falsely decreased free/total ratio. Therefore, prostate-specific antigen free/total ratio would be more reliable if interpreted in combination with information about CRP. However, it is recommended to defer the measurement of free/total ratio if CRP is highly elevated.