Empeiria

Prostate specific antigen, total

Also known as PSA, prostate specific antigen

protein · no single molecular formula

LOINC 2857-1 code verified serum ng/mL

What this substance is

A glycoprotein enzyme of about 30 kDa made by the prostate, with no single small molecule to draw. Its shape is a 3D question.

UniProt P07288

3D model · Protein (predicted)

Predicted structure of PSA, one chain (AlphaFold). PSA works as a single chain. Predicted by AlphaFold (model v6, average confidence 92 of 100); its sequence matches UniProt exactly. Colour is AlphaFold's own confidence for each part: dark blue very high (above 90), light blue confident (70-90), yellow low (50-70), orange very low (below 50). Drag to rotate, scroll to zoom.

Reference ranges

Checking your own result against this range needs the running application; this is a static copy. Nothing you type anywhere in Empeiria is ever sent to a server.

male
4
normal range · ng/mL
Applies toNormalOptimalCritical
male ≤ 4 ng/mL — —

guideline limit Prostate-Specific Antigen (PSA) Test, National Cancer Institute cited · not yet checked by a person

How it is measured

In practice

A health worker takes a small blood sample from a vein in your arm. Do not have sex or masturbate for 24 hours before the test, because releasing semen can raise PSA. Tell your provider about your medicines, since some can make PSA read falsely low. Do not test soon after a urinary infection or a procedure on the urinary system.

Total PSA is measured on a venous blood sample. Ejaculation should be avoided for 24 hours beforehand, and testing deferred after a urinary tract infection or urological procedure; cystoscopy, prostate biopsy, catheterisation, prostatitis and recent colonoscopy can raise PSA. Some medicines lower PSA falsely. A raised result is often repeated, commonly within 3 months, and free PSA may be added.

Before the test

  • Avoid sex and masturbation (ejaculation) for 24 hours before the test.
  • Tell your provider about all medicines you take; do not stop any unless told to.
  • Do not have the test soon after a urinary tract infection or a urinary procedure or surgery; ask how long to wait.

Where: laboratory

Sources: Prostate-Specific Antigen (PSA) Test -- MedlinePlus Medical Tests, U.S. National Library of Medicine; Prostate-specific antigen (PSA) blood test -- MedlinePlus Medical Encyclopedia, U.S. National Library of Medicine cited · not yet checked by a person

In the lab

immunoassay

Total PSA immunoassay

PSA floats in blood both on its own and stuck to another protein. The test uses antibodies that latch onto both kinds, and a machine compares the signal with samples of known PSA amounts.

Total PSA is measured by immunoassay using antibodies intended to detect both free PSA and PSA complexed to alpha-1-antichymotrypsin (PSA-ACT), the main immunoreactive forms in serum; results are read off a calibration curve built from PSA calibrators.

  • Read by: Signal from labelled antibody bound to PSA, converted to concentration via the calibration curve
Why labs disagree: PSA results depend on the calibrator: assays calibrated to the WHO PSA standards have been reported to give total PSA results 20–25% lower than when calibrated to the Hybritech standard. Calibrators purified from seminal plasma contain differing amounts of intact and cleaved PSA forms, and not all assays respond equally to free and complexed PSA, which contributes to value differences between manufacturers.

Source: McJimpsey EL (NIST). Molecular Form Differences Between Prostate-Specific Antigen (PSA) Standards Create Quantitative Discordances in PSA ELISA Measurements. Sci Rep 2016 (PMC open access) cited · not yet checked by a person

What it reports on

Associated symptoms

Conditions this marker features in