Acid Phosphatase is normally found in many tissues, including liver, red blood cells, bone marrow, and platelets. The highest levels are found in the prostate gland—the Prostatic Acid Phosphatase (PAP) isoenzyme. Usually (but not always) elevated levels are seen in patients with prostatic cancer that has metastasized beyond the capsule to other parts of the body, especially bone. The degree of elevation indicates the extent of disease.
Because acid phosphatase is also found at high concentrations in seminal fluid, this test can be performed on vaginal secretions to investigate alleged rape. This is now the primary use of PAP testing. High levels of acid phosphatase also exist in white blood cells (mostly monocytes and lymphocytes). They are helpful in determining the clinical course of patients with lymphoproliferative diseases and hairy cell leukemia. Acid phosphatase is a lysosomal enzyme. Therefore lysosomal storage diseases (such as Gaucher disease and Niemann-Pick disease) are associated with elevated levels.
In males, one half of the total acid phosphatase (nearly all of the PAP) is found in the prostate gland. Lesser amounts are found in the liver, spleen, blood cells, and bone marrow. In females, total acid phosphatase is from the liver, red blood cells (RBCs), and platelets.
Acid phosphatase can be identified by cellular hydrolysis of naphthol phosphoric acid. The optimal pH for this reaction is on the acid side. When tartaric acid is added to the solution, hydrolysis of the substance by acid phosphatase is inhibited in prostate cells but not in the cells of hairy cell leukemia. The identification of tartrate-resistant acid phosphatase (TRAP) in white blood cells is therefore helpful in the diagnosis of hairy cell leukemia (and occasionally other lymphoproliferative diseases). It is important to note, however, that the specimens of 5% of patients with hairy cell leukemia are not tartrate resistant. In the past decade, radioimmunoassay and enzyme-linked immunosorbent assay kits have been used to determine acid phosphatase levels (specifically PAP). These methods are more accurate than the biochemical methods previously described and are more easily performed.
Causes of False Acid Phosphatase test results
- Falsely high levels of acid phosphatase (and specifically PAP) may occur in males after a digital rectal examination or after instrumentation of the prostate (e.g., cystoscopy) because of prostatic stimulation. Elevated levels of 25% to 50% may occur for up to 48 hours after prostate manipulation. The test should be repeated if elevated levels occur after a rectal or prostate examination.
- Acid Phosphatase is heat and pH sensitive, and acid phosphatase activity will decrease if left for long time in room temperature .
- Drugs that may cause increased levels of acid phosphatase include alglucerase, androgens (in females), and clofibrate (Atromid-S).
- Drugs that may cause decreased levels include alcohol, fluorides, heparin, oxalates, and phosphates.
Normal Acid Phosphatase Levels
Newborns normally have higher Acid Phosphatase Levels than adults. Normal Acid Phosphatase levels decrease by aging. The following is a listing of Normal Acid Phosphatase Levels:
- Newborn: 10.4 to 16.4 units/mL at 30° C (86° F).
- Child: 8.6-12.6 units/mL at 30° C (86° F ).
- Adult: 0.13 to 0.63 units/L at 37° C (98.6° F).
Causes of High Acid Phosphatase Levels
- Acid Phosphatase (and specifically PAP) exist in the Pysosomes of Prostate cells. Diseases affecting prostate tissue will destroy those cells, and the lysosomal contents will spill into the bloodstream, where they will be detected. This can be an indication of Prostatic Carcinoma, Benign Prostatic Hypertrophy, or Prostatitis.
- Because acid phosphatase exists in the lysosomes of the bone marrow, diseases affecting the bone will be associated with elevated blood levels. This may indicate Multiple Myeloma, Paget Disease, Hyperparathyroidism, or Metastasis to the Bone.
- Because acid phosphatase exists in the lysosomes of blood cells, diseases affecting blood cells will be associated with elevated blood levels. This can be caused by Multiple Myeloma, Sickle Cell Crisis, or Thrombocytosis.
- Lysosomal Disorders (Gaucher Disease for example): Because acid phosphatase exists in the lysosomes of many tissues affected by these diseases, elevated blood levels can be expected.
- Renal and Liver diseases, such as cirrhosis: Because acid phosphatase is present in these organs, diseases affecting these organs will be associated with elevated blood levels. Rape: PAP will be elevated in vaginal secretions of a woman having been recently raped. The PAP assay is a well-documented presumptive assay for the presence of semen.