Stability of prostate specific antigen (PSA) in blood samples
Evidence Overview
Background
- In NHSScotland, total prostate specific antigen (PSA) levels are measured as a first line test for men presenting in primary care with symptoms suggestive of prostate cancer.
- Total PSA levels in whole blood or serum are more stable over time than free PSA levels.
- Variation in total PSA levels in samples remained below 5% change from baseline for approximately 3 days at room temperature. Changes in free PSA levels exceeded 5% within about 24 hours, even at refrigerated temperatures. A 5% change from baseline is viewed as a clinically important change that affects the accuracy of the test result.
- Refrigerating blood or serum samples for PSA testing slows down the changes in total and free PSA levels before testing.
- Storing serum on the clot or allowing blood to coagulate leads to larger and faster changes in total and free PSA levels.
- A requirement to test total PSA levels within 24 hours has potential implications for NHS Boards serving people living in remote, rural and island communities in Scotland.
