Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1111 page)

   Use of wrong anticoagulant rather than the recommended 3.2% sodium citrate (currently used in blue top tubes)

Analytic Pitfalls

   Hemolyzed, severely icteric, or hyperlipemic blood may affect results (modern equipment may override icteric or hyperlipidemic blood)

Other Limitations: Drugs

   Short values may be seen with estrogen therapy or oral contraceptives.

   Prolonged values may result from diphenylhydantoin, naloxone, and radiographic contrast agents.

PERIPHERAL BLOOD SMEARS (PBS)
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   Definition

   The primary purpose of studying PBS is to obtain differential counts of WBC and to study blood cell morphology.

   Use

   Blood collected for CBC is prepared manually (or by automated equipment), smearing a thin layer of blood on a glass slide, and then staining with special dyes for microscopic examinations. They are most helpful for the rapid identification of anemias, leukemias, and platelet abnormalities. PBS are also studied for the presence of organisms. When malaria is suspected, the PBS (thin smear) is most useful in finding and identifying parasites (thick film: a concentrated technique by which a large amount of blood is placed in a small area; it is used in cases with sparse parasites).

   Special stains may be added to provide additional diagnostic information:

   Leukocyte (neutrophil) alkaline phosphatase: normal range is 11–95. It is an absolute value derived for counting the leukocyte granules at the microscope. It is used primarily to differentiate between CML and leukocytosis of other etiologies. It is decreased in myeloid cells of CML patients and in some cases of myelodysplastic syndrome, as well as in pernicious anemia and PNH. It is increased in leukemoid reactions and myeloproliferative neoplasms.

   Myeloperoxidase: Stains primary granules of neutrophils and secondary granules of eosinophils, identifying myeloid lineage (helpful for blast lineage identification in leukemias).

   Specific (naphthol AS-D chloroacetate esterase) identifies cells of myeloid series but not monocytes or lymphocytes.