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Introduction ⬇

The periodic acid–Schiff (PAS) stain aids in the diagnosis of ALL. Early myeloid precursors and erythrocyte precursors are negative. As granulocytes mature, they increase in PAS positivity, whereas mature RBCs stay negative. The PAS stain cannot be used to distinguish between ALL and AML or between benign and malignant lymphocytic disorders.

Normal Findings ⬆ ⬇

Lymphoblasts: stain (positive)

Myeloblasts: do not stain (negative)

Procedure ⬆ ⬇

  1. Obtain bone marrow aspirate.

  2. Prepare slide, stain with PAS, and scan microscopically.

Clinical Implications ⬆ ⬇

  1. Positive reaction

    1. Blasts in ALL in childhood often have coarse clumps or masses of PAS-positive material within their scent cytoplasm. The staining pattern is usually heterogeneous, with some cells containing PAS-positive clumps and others virtually unstained.

    2. AML

    3. Hairy cell leukemia

    4. Sézary syndrome

    5. Conspicuous PAS positivity in the erythroid precursors is strongly suggestive of erythroleukemia (M6)

  2. Weakly positive

    1. In acute granulocytic leukemia, the blasts display either a negative or weakly positive, finely granular pattern.

    2. In some cases of thalassemia and in anemias with blocked or deficient iron, the RBC precursors also contain PAS-positive material.

    3. Hodgkin lymphoma

    4. Infectious mononucleosis

  3. Negative stain

    1. Lymphoblasts of Burkitt lymphoma

    2. Megaloblastic leukemia

Interventions ⬆

Pretest Patient Care

  1. Explain test purposes and procedures.

  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.

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