Comparative study of assays for prostate-specific antigen molecular forms.

Area of Science:

• Clinical Chemistry
• Biomarker Detection
• Prostate Cancer Diagnostics

Background:

• Prostate-specific antigen (PSA) molecular forms, including free PSA and PSA-ACT, improve prostate cancer diagnostic accuracy in patients with borderline elevated PSA levels.
• However, inconsistencies exist in serum free PSA and PSA-ACT values across different assays, hindering reliable clinical application.

Purpose of the Study:

• To evaluate the correlation and agreement among serum free PSA and PSA-ACT values obtained from various commercially available assays.
• To establish conversion equations for standardizing measurements across different kits.

Main Methods:

• Serum free PSA and PSA-ACT were measured using multiple assay kits: Hybritech, DPC, EIKEN, Abbott, Roche, and Can-Ag for free PSA; Dainippon, Chugai, EIKEN, and Bayer for PSA-ACT.
• Data from each assay were compared against Hybritech (free PSA) and Dainippon (PSA-ACT) standards.

Main Results:

• Free PSA data from Hybritech, EIKEN, Abbott, and Can-Ag kits showed similarity.
• DPC and Roche kits demonstrated linear relationships with Hybritech, requiring conversion factors (a=1.20 and 1.57).
• PSA-ACT values from Dainippon and Chugai were identical; EIKEN required a conversion equation (0.7636x + 0.1381).

Conclusions:

• Serum free PSA and PSA-ACT values are assay-dependent and not always interchangeable.
• Specific assay kits provide consistent results, while others necessitate validated conversion equations for accurate interpretation.
• Gamma-Sm measurements exhibited significant variability and are not recommended for free PSA assessment.