Prostate-Specific Antigen (PSA) Test
The PSA test consists of a blood analysis that detects abnormal levels of the protein responsible for facilitating sperm motility, which may indicate a prostate pathology.
General Description
The prostate-specific antigen (PSA) test measures the amount of PSA, a protein produced by the prostate to liquefy semen, present in the blood. This protein is primarily found in semen, but a small portion (less than 4 ng/mL up to age 70 and less than 6.5 ng/mL thereafter) circulates in the blood of any healthy man. Blood PSA levels gradually increase with age or when the prostate enlarges. A sudden rise to very high levels may indicate infection (prostatitis), inflammation, benign prostatic hyperplasia, or prostate cancer. Generally, values between 4 and 10 ng/mL are considered borderline, with approximately 25% associated with a malignant tumor. Levels above 10 ng/mL increase the risk to 50%.
To confirm the diagnosis of a prostate condition, additional complementary tests are required. Therefore, the PSA test is primarily used to detect abnormalities or rule out disease in selected patient groups as a screening tool.
When is it indicated?
The PSA test is performed when there is suspicion of prostate disease or routinely in men aged 55 to 69 with risk factors. It is used to diagnose the following conditions:
- Prostate cancer
- Benign prostatic hyperplasia: enlargement of the gland without the presence of cancerous cells
- Prostatitis: inflammation of the prostate
How is it performed?
The PSA test is performed via a blood sample collected in the same manner as a routine blood test:
- The patient sits or lies on an examination table with the arm extended and fist closed.
- A tourniquet is applied above the elbow.
- After disinfecting the area, a needle is inserted into a vein in the forearm.
- The tourniquet is released as the patient opens their hand.
- Once the tube is filled (yellow cap, containing a separating gel and a clotting additive for laboratory analysis), the needle is removed.
In the laboratory, the sample is centrifuged to separate plasma from serum, and various techniques are used to quantify PSA levels:
- ELISA (enzyme-linked immunosorbent assay): enzyme-labeled antibodies react with a streptavidin-biotin substrate, generating a color change that allows identification of the number of PSA molecules.
- Chemiluminescence: an advanced technique that uses light to detect PSA. Specific antibodies labeled with a luminescent molecule bind to PSA, then a reagent is added to oxidize the luminophore, emitting light. This light is detected with a chemiluminometer to determine PSA concentration.
Risks
The PSA analysis does not pose a risk to the patient, although a hematoma may appear at the needle insertion site.
What to expect from a PSA test
The patient is only required to be present on the day of blood collection. Fasting is generally not necessary unless the sample will be used for other parameter studies.
Although not a painful procedure, some patients with higher sensitivity may experience discomfort during needle insertion, which usually resolves quickly. Patients prone to dizziness should lie down during the procedure and remain at rest afterward to prevent complications.
It is recommended not to bend the arm and to apply pressure to the puncture site to avoid hematoma formation.
Typically, results are available within one to two days. If results are positive, the specialist will explain the next steps in a follow-up consultation.
Specialties in which the PSA test is requested
The PSA test is requested in the specialty of Urology.
How to prepare
In the days prior to a PSA blood test, certain recommendations should be followed to avoid altered results:
- One week before: avoid other prostate-related medical procedures, such as digital rectal examination or transrectal ultrasound.
- 24–48 hours prior:
- Avoid ejaculation
- Avoid intense physical exercise
The specialist will advise if any ongoing medications should be temporarily suspended. Additionally, urinary tract infections should be monitored, and if present, the procedure may be postponed.
