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Introduction ⬇

Electrophoresis, or separation, of LDH identifies the five isoenzymes of fractions of LDH—each with its own physical characteristics and electrophoretic properties. Fractioning the LDH activity sharpens its diagnostic value because LDH is found in many organs. LD isoenzymes are released into the bloodstream when tissue necrosis occurs. The isoenzymes are elevated in terms of the patterns established, not on the basis of the value of a single isoenzyme. The origins of the LDH isoenzymes are as follow: LD1 and LD2 are present in cardiac tissue and erythrocytes; LD3 originates mainly from the lung, spleen, pancreas, and placenta; and LD4 and LD5 originate from skeletal muscle and liver.

The five isoenzyme fractions of LDH show different patterns in various disorders. Abnormalities in the pattern suggest which tissues have been damaged. This test is useful in the differential diagnosis of megaloblastic anemia (e.g., folate deficiency, pernicious anemia), hemolytic anemia, and, very occasionally, renal infarct. These entities are characterized by LD1 increases, often with LD1:LD2 inversion (flip).

Normal Findings ⬆ ⬇

LD1: 17%–27% of total or 0.17–0.27

LD2: 29%–39% of total or 0.29–0.39

LD3: 19%–27% of total or 0.19–0.27

LD4: 8%–16% of total or 0.08–0.16

LD5: 6%–16% of total or 0.06–0.16

Procedure ⬆ ⬇

  1. Obtain a 5-mL venous blood sample (red-topped tube). Serum is needed.

  2. Avoid hemolysis.

  3. 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.

Clinical Implications ⬆ ⬇

  1. Abnormal LD1 and LD2 patterns reflect damaged tissues (Table 6.12).

    1. The appearance of an LD flip (i.e., when LD1 level is higher than LD2 level) is helpful in the diagnosis of hemolytic, megaloblastic, and sickle cell anemia. This is because RBCs have an isoenzyme pattern similar to that of heart muscle. The time elapsed to peak values may help to differentiate these conditions.

  2. LD3 increases occur in advanced cancer and malignant lymphoma; this level should decrease following effective therapy. LD3 is occasionally elevated with pulmonary infarction or pneumonia.

  3. LD5 is increased in the following conditions:

    1. Liver disease, hepatitis

    2. Heart failure, pulmonary edema

    3. Striated muscle trauma, burns

  4. LD5 increase is more significant when LD5/LD4 ratio is increased.

  5. In most cancers, one to three of the bands (LD2, LD3, and LD4) are frequently increased. A notable exception is in seminomas and dysgerminomas, in which LD1 is increased. Frequently, an increase in LD3 may be the first indication of the presence of cancer.

  6. All LD isoenzymes are increased with systemic diseases (e.g., carcinomatosis, collagen vascular disease, disseminated intravascular coagulation, sepsis) (see Table 6.12).

  7. Increased total LD with normal distribution of isoenzymes may be seen in coronary artery disease (CAD) with chronic heart failure, hypothyroidism, infectious mononucleosis and other inflammatory states, uremia, and necrosis.

Clinical Alert

LDH isoenzymes should be interpreted in conjunction with clinical findings

Interventions ⬆

Pretest Patient Care

  1. Explain test purpose and procedure. Repeat testing on 3 consecutive days is likely. Obtain pertinent clinical signs and symptoms.

  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 abnormal LD patterns and pulmonary infarction.

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