Phosphatases are enzymes that cleave phosphate from compounds with a single phosphate group. Those that are optimally active at pH 5 are grouped under the name acid phosphatase (ACP).

Many tissues (kidneys, spleen, liver, bone) contain ACP, but the prostate gland, red blood cells (RBCs), and platelets are especially rich in this activity. Two isoenzymes, prostatic fraction and RBC/platelet fraction, are diagnostically significant. These isoenzymes differ from one another in preferred substrate and in the degree to which they are inhibited by various additives during laboratory testing. Normal serum contains more RBC/platelet than prostatic ACP, and small changes in prostatic fraction may be difficult to detect. Tartaric acid inhibits prostatic ACP. Thus, many laboratories report tartrate-inhibitable ACP as well as total ACP in an effort to focus more specifically on the prostatic fraction.

Decreased levels of prostatic ACP are seen after estrogen therapy for prostatic carcinoma and in clients with Down syndrome. Decreased levels are associated with ingestion of alcohol, fluorides, oxalates, and phosphates.

Administration of androgens in women and of clofibrate in both genders produces elevated levels.

• Prostatic massage or rectal examination within 48 hours of the test may cause elevated levels.
• Administration of androgens in females and of clofibrate in either gender may produce elevated levels.
• Ingestion of alcohol, fluorides, oxalates, and phosphates may result in decreased levels.

• Enlarged prostate gland, especially if prostatic carcinoma is suspected:
  • Prostatic ACP is elevated in 50 to 75 percent of individuals with prostatic carcinoma that has extended beyond the gland.
  • Cancers that remain within the gland cause ACP elevation in only 10 to 25 percent of those affected.
  • Benign hyperplasia, inflammation, or ischemic damage to the prostate rarely causes elevated ACP levels.
• Evaluation of the effectiveness of treatment of prostatic carcinoma:
  • ACP levels fall to normal within 3 to 4 days of successful estrogen therapy.
  • Recurrent elevation strongly suggests that bone metastases are active.
• Support for diagnosing other disorders associated with elevated prostatic ACP levels (e.g., metastatic bone cancer, Paget's disease, osteogenesis imperfecta, hyperparathyroidism, and multiple myeloma)
• Known or suspected hematologic disorder:
  • Elevated RBC/platelet ACP is seen in hemolytic anemia, sickle cell crisis, thrombocytosis, and acute leukemia.
• Support for diagnosing other disorders associated with increased RBC/platelet ACP (e.g., renal insufficiency, liver disease, Gaucher's disease, and Niemann-Pick disease)

Nursing Care Before the Procedure

Client preparation is the same as that for any test involving the collection of a peripheral blood sample (see Appendix I).

• It is recommended that any drugs that may alter test results be withheld for 12 to 24 hours before the test, although this practice should be confirmed with the person ordering the study.

A venipuncture is performed and the sample collected in a red-topped tube. The sample should be handled gently to avoid hemolysis and transported promptly to the laboratory. If the test cannot be performed within a few hours, the serum should be frozen.

Nursing Care After the Procedure

Care and assessment after the procedure are the same as for any study involving the collection of a peripheral blood sample.

• Resume any drugs withheld before the test.
• Abnormal values: Note and report increased levels or associated levels of prostate-specific antigen. Provide support in coping with a life-threatening disease, hormonal therapy, and possible surgical procedure.