Prostate gland assay

Factors such as assay variations, age, and prostate gland size are known to affect cutoff values. Also, free to total PSA cutoffs are influenced by the sensitivity and specificity values chosen, the reflex range for total PSA used, differences in free PSA assays, and differences in populations studied. Different PSA values are considered due to differences in cutoffs in different assays. Studies have shown that the comparison of a chemiluminescent free PSA showed a 25 percent difference in values. These types of variations suggest a need for standardization (9,29). 

Ultrasensitive assays for PSA contribute to the earlier detection of prostate cancer relapse and (or) residual disease in prostatectomized patients as well as the more timely evaluation of response to current therapies. PSA determinations can be useful in detecting metastatic or persistent disease in patients following surgical or medical treatment of prostate cancer. Persistent elevation of PSA following treatment, or an increase in the pretreatment PSA concentrations, is indicative of recurrent or residual disease. Hence, PSA is widely accepted as an aid in the management of prostate cancer patients, and serum levels are most useful when sequential values are obtained and monitored over time. After complete removal of the prostate gland (radical prostatectomy), PSA levels should become very low or undetectable. A rise of the serum PSA level in prostatectomy patients indicates residual prostate tissue, recurrence, or metastasis of the disease (13, 16, 24, 36). 

PSA is one of the most widely used cancer biomarkers. It is a chymotryp-sin-like serine protease that is produced by epithelial cells of the prostate gland and secreted into the prostatic fluid. Prostate-cancer invasion disrupts the epithelial membrane barrier leading to elevated serum levels of PSA. Detection of PSA in blood can therefore be useful in the diagnosis of prostate abnormalities and for evaluation of prostate cancer therapy efficacy [21]. Two different forms of PSA are immunologically detectable the free form (MW 34 kDa) and a complex with a-l-antichymotrypsin (MW 96 kDa). Diagnostic assays developed for detection of PSA (e.g., enzyme-linked immunosorbent assays) detect total PSA concentrations down to 0.1 ngmL [22,23]. 

---