AN ANALYTICAL COMPARISON OF THE 3 MOST COMMONLY USED PROSTATE-SPECIFIC ANTIGEN ASSAYS - TANDEM-R, TANDEM-E, AND IMX

Objectives. To compare the similarity of individual prostate-specific antigen (PSA) results when using the Tandem-R PSA assay, the Tandem-E PSA assay, or the IMx PSA assay; to assess the lot-to-lot variation within (intra-assay interlot) and between (interassay interlot) the Tandem-R, Tandem-E, and IMx PSA assays; and to evaluate the individual and overall potential lot-to-lot bias of the Tandem-R, Tandem-E, and IMx PSA assays. Methods. Forty-nine serum samples (PSA values from 0 to 85 ng/mL) were each tested by three separate lots (manufacturer's reagent materials) of Tandem-R, Tandem-E, and IMx PSA assays, Therefore, a total of nine different lots were utilized per patient sample in this investigation. Analyses primarily focused on three ranges: 0 to 10 ng/mL (low), 10 to 85 ng/mL (high), and 0 to 85 ng/mL (overall). Results, In the 0 to 10 ng/mL range, 93% of the assay comparisons yielded an actual difference of less than 1 ng/mL. All three assays demonstrated excellent correlation within and between their three respective lots, within all three ranges. The 95% confidence intervals around the percent coefficient of variation (CV) demonstrated similar results for each assay (CV range, 3.2% to 6.0%). All lots demonstrated an average actual PSA bias of less than +/- 1 ng/mL. The average percent PSA bias was also similar between all three assay systems, All lots demonstrated a less than +/- 4% bias. Conclusions. Overall, the Tandem-R and IMx PSA assays yielded slightly lower results than the Tandem-E PSA assay. However, these differences were not statistically significant. In addition, the overall lot-to-lot variation (intra-assay and interassay) was not statistically significant, and the actual or percent PSA bias was minimal with these three assays. Therefore, a clinician can feel confident that a patient's serum sample should yield a similar and interchangeable result, whether it is determined by the Tandem-R, Tandem-E, or IMx PSA assay system.