The patient was anemic, which explains the fatigue and lethargy. His platelet count was also low, possibly accounting for the bruising. The white count was elevated, with a large percentage designated as blasts. With such a finding, there is no doubt that the patient has acute leukemia since the typical range for acute leukemia is greater than 20% blasts.
Because of their morphology and consistent appearance, an initial guess would be that they are lymphoblasts (see image of Wright stained blood smear to the right), thus yielding a possible diagnosis of Acute Lymphoblastic Leukemia (ALL). However, further testing is needed. Other tests include:
- cytochemical analysis, which can help determine the lineage
- immunophenotyping
- cytogenetic analysis
- genetic testing.
The cytochemical analysis is the low-tech way of differentiating between lymphoblasts and myeloblasts. Cytochemical stains target structures found in either lymphoblasts and/or myeloblasts. The cytochemical profile of lymphoblasts is Periodic Acid Schiff (PAS) positive and myeloperoxidase, Sudan black B, and alpha-naphthyl butyrate esterase negative. The image below shows PAS-positive lymphoblasts with dark staining polysaccharides in the cytoplasm.
Most labs will not rely on cytochemical staining alone for diagnosis. When doing cytochemical analysis, it is important to do all stains because some myeloblasts can be PAS positive but also positive with some of the other stains.
The following pages will discuss the other three tests used to diagnose ALL.
