The most common PSA immunoassays detect which form?

The most common PSA immunoassays detect which form?

• A. Total PSA
• B. Free PSA
• C. PSA complexed with α1-antichymotrypsin
• D. PSA complexed with α2-macroglobulin

Answer: (A)

PSA in the blood appears in multiple forms, including free PSA and PSA bound to proteins such as α1-antichymotrypsin and α2-macroglobulin. The antibodies used in most PSA immunoassays recognize PSA regardless of whether it is free or bound, so the detected amount reflects the total PSA circulating in the serum. This makes total PSA the form most commonly measured and reported in routine testing, providing a reliable overall marker for screening and monitoring. Measuring free PSA is used selectively to improve specificity when total PSA is elevated, by calculating the ratio of free to total PSA. Specialized assays can quantify the complexed forms separately, but they are not the standard.

PSA in the blood appears in multiple forms, including free PSA and PSA bound to proteins such as α1-antichymotrypsin and α2-macroglobulin. The antibodies used in most PSA immunoassays recognize PSA regardless of whether it is free or bound, so the detected amount reflects the total PSA circulating in the serum. This makes total PSA the form most commonly measured and reported in routine testing, providing a reliable overall marker for screening and monitoring. Measuring free PSA is used selectively to improve specificity when total PSA is elevated, by calculating the ratio of free to total PSA. Specialized assays can quantify the complexed forms separately, but they are not the standard.