A comparison of three free and total PSA assays

Abstract

Prostate-specific antigen (PSA) has emerged as the most predictive test of whether or not a man has prostatic carcinoma. The free to total PSA ratio provides important enhancement in specificity, thus obviating unnecessary negative biopsies. In the absence of an international standard for total PSA, much less free PSA, variation between manufacturers may cause confusing results. We sought to compare three different manufacturer's free and total PSA assays in a population consisting of consecutive patients who had PSA testing in a reference laboratory in Germany. Between April 1994 and July 1996, serum specimens from 240 men were evaluated with three different free and total PSA assays. Indications for PSA determination were based on the referring physician, who also provided the clinical diagnosis. Total and free PSA were measured on the same freeze-thaw cycle with Chiron Diagnostics, Enzymun Boehringer Mannheim, and Hybritech Tandem-R assays. Seventy-nine men had carcinoma of the prostate, 120 had clinical evidence of benign prostatic hyperplasia and 27 were without evidence of prostatic disease. The Chiron ACS: 180 free to total ratio compared very well with the Tandem-R assay at the 95% sensitivity level, affording 17 and 22% specificity respectively. Using the range of total PSA of 4-10 ng/ml, the increase in specificity of the free to total PSA is quite significant, and the specificity of the Enzymun assays is greatly improved. (Specificity of 49%, 29% and 25% at 95% sensitivity for ACS, Enzymun and Tandem respectively.) This data, based on 'real world' clinical experience, shows significant variation between different manufacturers' assays. There was significant equivalence between the Chiron and Hybritech assays. The Enzymun assay performed well only when data from the total PSA range of 4-10 ng/ml was included. Clinicians must be aware of which manufacturers' assays for both the free and total PSA their laboratory staff is utilizing, and laboratory technicians must provide meaningful outcome data based on the patient population they serve with respect to the performance of these assays.

Prostate-specific antigen: current status

“…In a more recent investigation, we compared free assays and total PSA assays by three different manufacturers 57 . This investigation also confirmed substantial equivalence between the methods developed by Hybritech and Chiron, whereas discrepancies were discovered in results reported with the Boehringer tests (Table 10).…”

Prostate‐specific antigen

“…The measurement of two analytes potentially compounds the bias between different manufacturer assays. We have observed considerable bias in assays of total PSA [54,55] and also of free PSA [55]. More recently, we have demonstrated considerable bias when the free and total assays of the same manufacturer are compared with those of different manufacturers [54].…”

“…We have observed considerable bias in assays of total PSA [54,55] and also of free PSA [55]. More recently, we have demonstrated considerable bias when the free and total assays of the same manufacturer are compared with those of different manufacturers [54]. In this latter investigation, 240 sera from men coming in for routine PSA testing were compared utilizing three different manufacturers and their corresponding total assays.…”

“…Currently, we are carrying out a prospective screening study with this assay and have shown that cPSA identifies all men with prostate cancer who would be found with a total PSA of greater than 4.0 ng/ml with significant reduc- *Data from all patients in the benign prostatic hyperplasia and prostate cancer groups is included [54]. PSA, prostate-specific antigen; F/T, free to total.…”

Long-term stability of alpha-1-antichymotrypsin complexed form of prostate specific antigen

“…14 ± 17 Problems exist with this ratio, including so-called quotient bias resulting in potentially signi®cant discrepancy in clinical testing compared to what is found in the literature. 18,19 The free/total PSA ratio requires the measurement of two analytes, potentially doubling the cost of PSA testing.…”