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Introduction ⬇

PNH was first described by a patient who noted hemoglobinuria after sleep. In many patients, the hemolysis is irregular or occult. PNH is a hemolytic anemia in which there is also production of defective platelets and granulocytes. The diagnostic feature of PNH is an increased sensitivity of the erythrocytes to complement-mediated lysis. Although patients with PNH can present with hemoglobinuria or a hemolytic anemia, they may also present with iron deficiency (because of urinary loss of blood), bleeding secondary to thrombocytopenia, thrombosis, renal abnormalities, or neurologic abnormalities.

These tests are carried out to make a definitive diagnosis of PNH. The basis of these tests is that the cells peculiar to PNH have membrane defects, making them extra sensitive to complement in the plasma. Cells from patients with PNH undergo marked hemolysis after 15 minutes in the laboratory test. The tests are performed for patients who have hemoglobinuria, bone marrow aplasia (hypoplasia), or undiagnosed hemolytic anemia; they may be useful in the evaluation of patients with unexplained thrombosis or acute leukemia.

Normal Findings ⬆ ⬇

Negative or <1% hemolysis

Procedure ⬆ ⬇

  1. Obtain a venous blood sample of 5 mL anticoagulated with EDTA. 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. Mix the patient’s RBCs with normal serum and also with the patient’s own serum, acidify, incubate at 37 °C, and examine for hemolysis. Normally, there should be no lysis of the RBCs in this test (also called Ham test).

  3. Be aware that a separate test called the sugar water test or sucrose hemolysis test may also be done at this time.

Clinical Implications ⬆ ⬇

A positive test (hemolysis) is found in:

  1. PNH: A positive test (10%–50% lysis) is needed for diagnosis. The sucrose hemolysis test is also positive in PNH.

  2. Hereditary erythroblastic multinuclearity associated with a positive acidified serum test: The sucrose hemolysis test is negative.

Interventions ⬆ ⬇

Pretest Patient Care

  1. Explain test purpose and procedure.

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

Posttest Patient Care

  1. Review test results; report and record findings. Modify the nursing care plan as needed. Counsel the patient regarding abnormal findings; explain the need for possible follow-up testing and treatment. Monitor for anemia.

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

Interfering Factors ⬆

  1. False-positive results may be obtained with the following:

    1. Blood containing large numbers of spherocytes (hereditary or acquired)

    2. Dyserythropoietic anemia

    3. Specimen >8 hours old, specimen hemolyzed

    4. Aplastic anemia

    5. Leukemia and myeloproliferative syndromes

  2. These conditions can be distinguished from PNH by the fact that hemolysis occurs in both acidified serum and complement. In PNH, hemolysis occurs only in complement (complement dependent).