Monitoring percent free PSA in serial specimens: Improvement of test specificity, early detection, and identification of occult tumors

Abstract

We have measured the serum concentration of prostate specific antigen (tPSA) and determined the percent free PSA (% fPSA) in serial specimens from 64 patients with prostate cancer, 35 patients with benign prostate hyperplasia (BPH), and 3 patients with prostitis. We found that the % fPSAs were not a constant for individual patients during the course of the disease. When we compared only the % fPSA of the first specimen of serial specimens from individual patients, who were largely untreated, 37% of BPH specimens were above 22%, whereas only 1.6% cancer samples were above that value. We also found that 67% of cancer specimens and 14% of BPH samples were below 8%, respectively. Although % fPSA distribution pattern remained similar between two types of specimens, less differentiation was found between BPH and prostate cancer in random specimens compared to the study using first specimens of an individual patient's serial samples. Percent fPSA apparently are affected by treatment. However, the most important benefit for the determination of % fPSA appears to be the sensitivity of % fPSA to identify occult tumors when the tPSAs were in the normal concentration range. Determination of % fPSA also seems to improve the specificity of tPSA, not only during screening for the differentiation between BPH and prostate cancer, but also during monitoring of treatment and recurrence. J. Clin. Lab. Anal. 12:26–31, 1998. © 1998 Wiley‐Liss, Inc.

Biological Variation of Total Prostate-Specific Antigen: A Survey of Published Estimates and Consequences for Clinical Practice

“…We subsequently back-calculated the CV b by subtracting CV a from CV t : CV b ϭ ͌ CV t 2 Ϫ CV a 2 (7 ). Fifteen studies reported considerable variability of serial tPSA concentrations, but it was impossible to derive the CV b because of sufficient information on CV t and CV a was lacking (33)(34)(35)(36)(37)(38)(39)(40)(41)(42)(43)(44)(45)(46)(47).…”

Impact of assay parameters on the accuracy of free PSA test: Source and stability of calibrator, calibration curve fitting, and level of total PSA in the serum

“…In other words, determination of the %fPSA cutoff improves the specificity of prostate cancer screening in men with se-rum PSA levels between 4 and 10 ng/mL. The result of our own and other studies suggested that when the %fPSA is above a certain cutoff (e.g., in this case 23%) it is most likely that patients have BPH, whereas below a certain cutoff (such as 6%) they probably have cancer (8)(9)(10)(11). Because the concentration of serum fPSA is usually much lower than that of total serum PSA, any slight deviation of fPSA from its true value will conceivably impact the %fPSA calculation.…”

Thiophilic interaction chromatography facilitates detection of various molecular complexes of prostate‐specific antigen in biological fluids

“…3). It is well known that t-PSA values are often greater than the sum of the total of f-PSA and PSA±ACT complex [27]. It is perhaps due to the presence of different molecular forms of PSA besides the PSA± ACT complex.…”