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Introduction ⬇

The isoenzymes of ALP are produced in various tissues. AP-1, α2 is produced in the liver and by proliferating blood vessels. AP-2, β1 is produced by the bone and placental tissue. The intestinal isoenzyme AP-3, β2 is present in small quantities in group O and B individuals who are Lewis-positive secretors. Placental ALP is present in the last trimester of pregnancy.

Any patient with an elevation of serum total ALP is a candidate for ALP isoenzyme study. The ALP isoenzymes test is mainly used to distinguish between bone and liver elevations of ALP.

Normal Findings ⬆ ⬇

AP-1, α2: values (liver) reported as weak, moderate, or strong or 24–158 U/L (0.40–2.64 μkat/L)

AP-2, β1: values (bone) reported as weak, moderate, or strong or 24–146 U/L (0.40–2.44 μkat/L)

AP-3, β2: values (intestines) reported as weak, moderate, or strong or 0–22 U/L (0–0.36 μkat/L)

AP-4: values (placental) reported as weak, moderate, or strong. Placental AP-4 is found only in ­pregnant women

Procedure ⬆ ⬇

  1. Obtain a 5-mL fasting venous blood sample in a plain red-topped tube or serum separator tube (SST) tube. Serum is needed. Centrifuge blood promptly, within 30 minutes after draw.

  2. 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.

  3. Refrigerate if not tested immediately.

Clinical Implications ⬆ ⬇

  1. Liver (AP-1, α2) isoenzymes are elevated in hepatic and biliary diseases such as the following conditions:

    1. Cirrhosis (hepatic)

    2. Hepatic carcinoma

    3. Biliary obstruction, primary biliary cirrhosis

  2. Bone (AP-2, β1) isoenzymes are elevated in the following conditions:

    1. Paget disease (excessive breakdown and formation of bone tissue)

    2. Hyperparathyroidism

    3. Bone cancer, rickets (all types)

    4. Osteomalacia, osteoporosis

    5. Malabsorption syndrome

    6. Certain kidney disorders (uremic bone disease or renal rickets)

  3. Intestinal (AP-3, β2) isoenzymes are elevated in the following conditions:

    1. Intestinal infarction

    2. Ulcerative lesions of the stomach, small intestine, and colon

    3. Individuals with blood type O or B secrete intestinal isoenzymes 2 hours after a meal

  4. Placental (AP-4) isoenzymes are increased in the following conditions:

    1. Pregnancy (late in third trimester to onset of labor)

    2. Complications of pregnancy such as hypertension and preeclampsia

  5. Placental-like isoenzymes occur in some cancers (unidentified isoenzymes):

    1. Regan isoenzyme

    2. Nagao isoenzyme

Clinical Alert

  1. This test should not be done if the total ALP level is normal.

  2. For evaluation of the biliary tract, alternative tests such as GGT, leucine aminopeptidase, and 5′-nucleotidase studies are recommended over the ALP ISO test.

  3. ALP isoenzymes have little value in children and adolescents because bone and liver fractions are normally elevated.

  4. In pregnancy, marked decline of the placental isoenzyme is seen with placental insufficiency and imminent fetal demise.

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 levels. see Appendix E for drugs that affect outcomes.

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

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

  4. ALP levels decrease if blood is anticoagulated.

  5. ALP levels increase after fatty meals.