PSA Specimen Type
Prostate-Specific Antigen (PSA) is measured from serum or blood specimens. 1
Standard Specimen Collection
- Serum PSA is the gold standard specimen type used in clinical practice for prostate cancer screening, diagnosis, and monitoring 1
- PSA circulates in the bloodstream in two primary forms: bound to serum proteins (primarily alpha-1-antichymotrypsin) and unbound or free PSA (fPSA) 1
- Approximately 60-90% of circulating PSA is covalently bound to endogenous protease inhibitors, while the remainder circulates as free PSA 1
Alternative Collection Methods
- Capillary whole blood from finger-stick can be used with specialized point-of-care systems, though this is not yet standard practice 2, 3
- Finger-stick blood collection systems (such as the Claros® analyzer) require only 10 µL of blood and provide results in 10 minutes, with high correlation (R² = 0.982-0.985) to standard serum assays 2
- Diluted whole blood samples can be stabilized and transported for PSA analysis, though this requires modified assay techniques 3
Clinical Context
PSA is a glycoprotein produced exclusively by prostatic tissue and is secreted into prostatic ducts, with only minor amounts leaking into circulation from normal prostate tissue 4, 5, 6
- The release of PSA into serum is increased in prostatic disease, including both prostate cancer and benign prostatic hyperplasia (BPH) 4, 6
- PSA's absolute tissue specificity makes it valuable as a tumor marker, though it lacks disease specificity since both malignant and benign conditions elevate serum levels 5, 6
Important Caveats
- Serum PSA measurements should be confirmed by retesting if abnormal, as fluctuations can occur due to laboratory interassay variability or individual biologic variability 1
- Various factors can transiently elevate serum PSA, including urinary catheterization (particularly traumatic), prostatitis, and digital rectal examination 1
- Medications such as finasteride and dutasteride (5α-reductase inhibitors) lower serum PSA values and require multiplication by a factor of 2.3 for accurate interpretation 1