Prostate-Specific Antigen (PSA) with Free PSA Ratio and Total PSA Screening
This blood test measures prostate-specific antigen (PSA), a protein produced by the prostate gland, to help screen for or monitor prostate health. It includes calculations for free PSA and total PSA to assess risk.
["PSA tests help detect early signs of prostate issues, including cancer, by measuring protein levels in your blood."]
Key facts at a glance
- LOINC
- 109070-3
- Short code
- CA199
- Synonyms
- Cancer Ag19-9 Msmt SerPl
- Category
- chemistry
- Sample
- serum
- Container
- Serum separator tube (SST) or red-top vacutainer tube; plasma may be collected in lithium heparin or EDTA tubes
- Units
- N/A
- Ref low
- 0
- Ref high
- 37
- Critical range
- 0.5 N/A – —
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- Method
- Immunoassay (Chemiluminescent or Electrochemiluminescent)
- CPT
- 86301
- SNOMED
- 1152685006
- Specimen volume
- 1 mL of serum or plasma (minimum 0.5 mL)
- Stability
- Room temperature: 8 hours; Refrigerated (2-8°C): 7 days; Frozen (-20°C or below): 3 months. Avoid repeated freeze-thaw cycles.
- Hemolysis max
- 100
- Lipemia max
- 200
- Icterus max
- 50
- TAT
- 4–24 hours
- Order
- routine
What PSA Tests Measure
The test includes three key measurements: total PSA (the overall protein level), free PSA (the portion of PSA that isn’t bound to other substances), and the free PSA ratio (the percentage of free PSA relative to total PSA). These help doctors evaluate prostate health more precisely.
Why Total PSA Matters
Total PSA levels can rise with prostate inflammation, infection, or benign enlargement (BPH), as well as prostate cancer. However, higher PSA alone doesn’t always indicate cancer, so doctors use it alongside other factors.
Why Free PSA Ratio Matters
A higher free PSA ratio (typically >25%) suggests less concern for cancer, while a lower ratio may raise suspicion. This ratio helps narrow down whether further testing is needed.
When This Test Is Ordered
Doctors may recommend this test during routine checkups, when symptoms like urinary changes appear, or as part of follow-up for prostate concerns. It’s often used in screening or monitoring existing conditions.
Reference range
<37 U/mL (commonly cited upper reference limit; values may vary by assay manufacturer)N/A
No special patient preparation required. Fasting is not necessary. However, recent meals may cause minor physiological variations in some individuals.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Elevated PSA levels can signal prostate issues, including cancer, but they’re not definitive. Doctors use PSA alongside physical exams, imaging, and other tests to make accurate diagnoses. Regular monitoring helps track changes over time.
Short name
PSA Blood Test
Frequently asked questions
What does a PSA test measure?
Why is free PSA important?
Can PSA levels change with age?
Sources
- 1
- 2Lab Tests OnlineSource
- 3
Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.
This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.
If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.
Medically reviewed by WellAlly Editorial Team Last reviewed August 17, 2026. · Read our editorial policy