Prostate-Specific Antigen (PSA)

Overview

Prostate-Specific Antigen (PSA), also known as kallikrein-3 (KLK3), is a serum biomarker widely used for the early detection and monitoring of prostate cancer. It is a glycoprotein enzyme produced mainly by the epithelial cells of the prostate gland.

Prostate-Specific Antigen belongs to the serine protease family and functions to liquefy semen, allowing the release and mobility of spermatozoa. Structurally, PSA is a single-chain glycoprotein of approximately 34 kDa, composed of 237 amino acids, carbohydrate side chains, and multiple disulfide bonds.

In healthy men, Prostate-Specific Antigen is present at very low concentrations in the blood (<1 ng/mL) but is abundant in semen. Its half-life is around 2.2 days. Importantly, Prostate-Specific Antigen is not cancer-specific, as elevated levels may occur in both malignant and benign prostate conditions. Therefore, Prostate-Specific Antigen testing should be interpreted alongside clinical findings, PCA3 mRNA testing, and other diagnostic tools.

Symptoms

Prostate-Specific Antigen testing is usually performed when patients present with urinary or systemic symptoms suggestive of prostate disease. Clinical indications include:

1. Urinary Symptoms:
   1. Frequent urination, especially night-time frequency (nocturia)
   2. Difficulty starting or stopping urination
   3. Weak urine flow
   4. Recurrent urinary tract infections (UTIs)
   5. Hematuria (blood in urine)
2. Systemic Symptoms:
   1. Severe bony pain in ribs, vertebrae, or sternum (suggesting metastasis)
   2. Unexplained metastatic deposits in bones in men
   3. General fatigue and discomfort

These symptoms often prompt Prostate-Specific Antigen testing for differentiation between prostate cancer, benign prostatic hyperplasia (BPH), and prostatitis.

Causes

Elevated Prostate-Specific Antigen levels can arise from both cancerous and non-cancerous conditions:

1. Malignant Causes:
   1. Prostate cancer
   2. Metastatic prostate cancer (often in bones or distant organs)
2. Benign Causes:
   1. Benign glandular hyperplasia (BPH)
   2. Prostate infections (prostatitis) or inflammation
   3. Recent urinary procedures or catheterization
   4. Blood sample collected immediately after digital rectal examination (DRE), which can falsely elevate PSA

This lack of specificity highlights the importance of correlating Prostate-Specific Antigen values with clinical assessment and confirmatory tests.

Risk Factors

Certain groups of men are at increased risk of abnormal PSA results and underlying prostate pathology:

1. Age:
   1. PSA levels naturally increase with age.
   2. Reference ranges:
      1. Up to 40 years: ≤ 2.5 ng/mL
      2. 40–60 years: ≤ 4.0 ng/mL
      3. Above 60 years: ≤ 5.0 ng/mL
2. Genetic and Family History:
   1. Men with a family history of prostate cancer are more likely to develop elevated PSA levels.
3. Prostate Conditions:
   1. Benign prostatic hyperplasia and chronic prostatitis can elevate PSA.
4. Procedural Interference:
   1. PSA may be artificially raised after rectal examination or biopsy.
5. Cancer Progression Factors:
   1. Rapid PSA velocity (>0.75 ng/mL/year) and high PSA density (>0.15 ng/mL²) increase cancer risk.
   2. A reduced free-to-total PSA ratio (<25%) favors malignancy.
6. Lifestyle and Ageing:
   1. Older men with lifestyle-related health issues may show higher PSA variability.

Prevention

Though prostate cancer and Prostate-Specific Antigen elevation cannot be fully prevented, proactive measures improve early detection and outcomes:

1. Routine Screening and Monitoring:
   1. Men above 40 should undergo regular PSA testing combined with digital rectal examination (DRE).
   2. Include PCA3 mRNA testing for confirmation when PSA is elevated.
2. Accurate Test Practices:
   1. Collect 3 mL of blood in a plain tube (red-capped).
   2. Separate serum quickly and transport properly.
   3. Avoid sample collection immediately after rectal exams to prevent false positives.
3. Advanced PSA Parameters:
   1. Evaluate total PSA, free PSA, % free PSA, PSA velocity, and PSA density for more reliable interpretation.
4. Lifestyle Adjustments:
   1. Maintain a healthy diet, exercise regularly, and reduce risk factors for prostate enlargement and inflammation.
5. Clinical Correlation:
   1. Always interpret PSA values along with clinical symptoms, imaging, and biopsy results.

Through proper testing and preventive care, elevated Prostate-Specific Antigen levels can be accurately assessed, reducing unnecessary anxiety and ensuring timely prostate cancer management.