Acid phosphatase is an enzyme found in various tissues, with high concentrations in the prostate gland (prostatic fraction) and other cells like erythrocytes and leukocytes (total fraction). It catalyzes the hydrolysis of phosphate esters in acidic environments. Measuring acid phosphatase levels, particularly the prostatic fraction, is historically significant in diagnosing and monitoring prostate-related conditions, though its use has largely been replaced by more specific markers like PSA (prostate-specific antigen).
Sample Type:

Prostatic Fraction: Derived primarily from the prostate gland, used to assess prostate health.
Total: Includes contributions from prostate, liver, spleen, red blood cells, and other tissues.

Clinical Significance:

Prostatic Fraction: Elevated levels may indicate prostate cancer, benign prostatic hyperplasia (BPH), or prostatitis. Historically used to monitor prostate cancer progression or metastasis, especially to bone.
Total Acid Phosphatase: Elevated in conditions like Gaucher’s disease, hemolytic anemia, or bone disorders, but less specific for prostate issues.

Testing:

Sample: Serum or plasma, with specific assays to differentiate prostatic fraction (e.g., tartrate-resistant acid phosphatase for non-prostatic sources).
Method: Enzymatic assays or immunoassays; prostatic fraction often measured using inhibitors to isolate prostate-specific activity.

Normal Range:

Prostatic Fraction: <2.5 ng/mL (varies by lab).
Total Acid Phosphatase: 0–6.5 U/L (varies by lab).

Limitations:

Less specific than PSA for prostate cancer.
Non-prostatic sources (e.g., hemolysis, liver disease) can elevate total levels.
Rarely used today due to PSA’s superior sensitivity and specificity.