Comparability of the tandem-R andIMx assays for the measurement of serum prostate-specific antigen

Abstract

Objectives.To assess the comparability of the Tandem-R and IMx serumprostate-specific antigen (PSA) assays across levels of the ratio of free-to-total serum PSA found in a community-based population of healthy men.Methods.Banked serum samples from the baseline component of the Olmsted CountyStudy of Urinary Symptoms and Health Status Among Men were thawed and analyzed using the Tandem-R and IMx PSA assays. Serum levels also were determined for the free, noncomplexed form of PSA, PSA complexed to alpha-1 antichymotrypsin, and total PSA with a research-based immunofluorometric assay.Results.The results of the Tandem-R and IMx assays were strongly correlated at alllevels of the ratio of free-to-total serum PSA. The Spearman correlation coefficients ranged from 0.87 to 0.98 (all p Conclusions.For the majority of men, results of the Tandem-R and IMx PSA assays were virtually identical. The small differences found would not be of clinical significance for most men but should be considered when comparing results of different assays in sequential determinations for a specific man.