What is the Difference Between Free PSA and Total PSA?
🆚 Go to Comparative Table 🆚The main difference between free PSA and total PSA lies in their binding to other proteins in the blood. Prostate-specific antigen (PSA) is a protein produced by prostate cells, and it circulates in the blood in two ways: bound to other proteins or unbound (free).
- Free PSA: This is the unbound PSA that circulates freely in the blood. A free PSA test measures the percentage of unbound PSA in the blood.
- Total PSA: This measured amount includes both free and bound PSA in the blood.
Doctors often use both tests together to determine the likelihood of prostate cancer. A higher ratio of free PSA to total PSA indicates a lower risk of prostate cancer, while a lower ratio indicates a higher risk. If a man's total PSA level is between 4 and 10 ng/ml, doctors may test the blood for free PSA. A percent-free PSA above 25% is considered normal, while a lower percentage may warrant further investigation, such as a biopsy.
In summary, the main difference between free PSA and total PSA is their binding status in the blood. Free PSA circulates freely, while total PSA includes both free and bound PSA. The ratio of free to total PSA can help determine the risk of prostate cancer, and both tests are often used together for a more accurate assessment.
Comparative Table: Free PSA vs Total PSA
The difference between free PSA and total PSA lies in their binding to other proteins and their concentration in the blood. Here is a table summarizing the differences:
Parameter | Free PSA | Total PSA |
---|---|---|
Definition | Free PSA is the percentage of unbound PSA circulating in the blood. | Total PSA measures the total amount of both free and bound PSA in the blood. |
Binding | Unbound | Bound to other proteins. |
Concentration | Lower in cases of prostate cancer. | Higher in cases of prostate cancer. |
Testing | Tests are done on patients with total PSA levels between 4 ng/ml and 10 ng/ml. | Tests are done to measure the amount of PSA in the blood. |
Ratio | The free-to-total PSA ratio is calculated by dividing the free PSA concentration by the total PSA concentration. | Not applicable. |
Comparing total PSA levels with free PSA levels can give an idea of the risk of having prostate cancer. A total PSA level between 4 and 10, doctors may test your blood for free PSA. A percent-free PSA above 25% is considered normal.
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