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Introduction ⬇

Alkaline phosphatase (ALP) is an enzyme originating mainly in the bone, liver, and placenta, with some activity in the kidney and intestines. It is called alkaline because it functions best at a pH of 9. ALP levels are age and gender dependent. Postpuberty ALP is mainly of liver origin.

ALP is used as an index of liver and bone disease when correlated with other clinical findings. In bone disease, the enzyme level rises in proportion to new bone cell production resulting from osteoblastic activity and the deposit of calcium in the bones. In liver disease, the blood level rises when excretion of this enzyme is impaired as a result of obstruction in the biliary tract. Used alone, ALP may be misleading.

Normal Findings ⬆ ⬇

Adults: 52–142 U/L

Normal values are higher in pediatric patients and in pregnant women. Values increase up to three times in puberty. Check with your laboratory for reference values. Values may vary with method of testing.

Procedure ⬆ ⬇

  1. Obtain a 5-mL fasting venous blood sample (red-topped tube). Serum is used for this test. Anticoagulants may not be used. Observe standard precautions. Label the specimen with the patient’s name, date and time of collection, and test(s) ordered. Place the specimen in a biohazard bag.

  2. Refrigerate sample as soon as possible.

  3. Note age and gender on test requisition.

Clinical Implications ⬆ ⬇

  1. Elevated levels of ALP in liver disease (correlated with abnormal liver function tests) occur in the following conditions:

    1. Obstructive jaundice (gallstones obstructing major biliary ducts; accompanying elevated bilirubin)

    2. Space-occupying lesions of the liver such as cancer (hepatic carcinoma) and malignancy with liver metastasis

    3. Hepatocellular cirrhosis

    4. Biliary cirrhosis

    5. Intrahepatic and extrahepatic cholestasis

    6. Hepatitis, infectious mononucleosis, cytomegalovirus

    7. Diabetes (causes increased synthesis), diabetic hepatic lipidosis

    8. Chronic alcohol ingestion

    9. Gilbert syndrome (hyperbilirubinemia)

  2. Bone disease and elevated ALP levels occur in the following conditions:

    1. Paget disease (osteitis deformans; levels 10–25 times normal)

    2. Metastatic bone tumor

    3. Osteogenic sarcoma

    4. Osteomalacia (elevated levels help differentiate between osteomalacia and osteoporosis, in which there is no elevation), rickets

    5. Healing factors (osteogenesis imperfecta)

  3. Other diseases involving elevated ALP levels include the following:

    1. Hyperparathyroidism (accompanied by hypercalcemia), hyperthyroidism

    2. Pulmonary and MIs

    3. Hodgkin disease

    4. Cancer of lung or pancreas

    5. Ulcerative colitis, peptic ulcer

    6. Sarcoidosis

    7. Perforation of bowel (acute infarction)

    8. Amyloidosis

    9. CKD

    10. Heart failure

    11. Hyperphosphatasia (primary and secondary)

  4. Decreased levels of ALP occur in the following conditions:

    1. Hypophosphatasia (congenital)

    2. Malnutrition, scurvy

    3. Hypothyroidism, cretinism

    4. Pernicious anemia and severe anemias

    5. Magnesium and zinc deficiency (nutritional)

    6. Milk-alkali syndrome (Burnett syndrome)

    7. Celiac sprue

Interventions ⬆ ⬇

Pretest Patient Care

  1. Explain test purpose and blood-drawing procedure. Fasting is required.

  2. Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

Posttest Patient Care

  1. Have patient resume normal activities.

  2. Review test results; report and record findings. Modify the nursing care plan as needed. Monitor appropriately for liver or bone disease and evidence of tumor. Testing for 5′-nucleotidase provides supportive evidence in the diagnosis of liver disease and a definitive diagnosis of Paget disease and rickets, in which high levels of ALP accompany normal (0–5 U/L or 0–0.08 μkat/L) or marginally increased 5′-nucleotidase activity.

  3. A useful test to confirm biliary abnormality is GGT. The GGT test is elevated in hepatobiliary disease, but not in uncomplicated bone disease.

  4. Follow guidelines in Chapter 1 for safe, effective, informed posttest care.

Interfering Factors ⬆

  1. A variety of drugs produce mild to moderate increases or decreases in ALP levels. see Appendix E for drugs that affect outcomes.

  2. Young children, those experiencing rapid growth, pregnant women, and postmenopausal women have physiologically high levels of ALP; this level is slightly increased in older persons.

  3. After IV administration of albumin, there is sometimes a marked increase in ALP for several days.

  4. ALP levels increase at room temperature and in refrigerated storage. Testing should be done the same day.

  5. ALP levels decrease if blood is anticoagulated.

  6. ALP levels increase after fatty meals.