Assay

Prostate Specific Antigen

Key Words

PSA

Specimen Collection

Serum (brown), Plasma (orange)

Turnaround Time

72hrs

Test Indications

Prostate specific antigen (PSA) is used as a tumour marker for prostate cancer. It can be used in diagnosis (in conjunction with DRE), where the higher the PSA concentration, the greater the probability of prostate cancer. Around 15% of men with PSA <4ug/L will have prostate cancer on biopsy, as will 25% of men with PSA 4-10ug/L and 50% of men with PSA >10ug/L. Confirmed levels of >100ug/L are consistent with metastatic disease.

Limitations/Interferences

No significant interferences from lipaemia, icterus, common drugs, rheumatoid factor etc.It is known that in rare cases PSA isoforms do exist which may be measured differently by different PSA tests. PSA is not known to be elevated in cancers of other origins, but a number of medical investigations or interventions (e.g. catherisation, cystoscopy, digital rectal examination, prostatic needle biopsy, prostatic massage, prostate ultrasonography, transurethral prostatic biopsy) can cause elevated concentrations, and 5-a-reductase inhibitors can decrease concentrations. Benign conditions that may cause elevated concentrations include acute urinary retention, benign prostatic hyperplasia, prostatitis and urinary tract infections.

Reference Range

0–49 yrs      up to 2.5 μg/L

50–69 yrs    up to 3.0 μg/L

70-79 yrs        up to 5.0 μg/L

80+ yrs         up to 10.0 μg/L

PSA cut offs are based on the criteria for referral via the 2WW pathway as recommended by NICE, with other age-related cut offs as suggested by local prostate cancer leads. If PSA elevated and this is a new finding, recommend repeat sample in 4 weeks. Referral is recommended when there are two elevated PSA results in the absence of urinary infection and recent ejaculation.

If new finding of significant PSA elevation (>10ug/L), suggest immediate referral to urology.

Analytical Error

3.5%

Reference Change Value

21.1%