“Arbitrary” criterion for the diagnosis of acute leukemia

Abstract

According to the WHO classification of acute leukemia, diagnosis is based on an arbitrary cut-off point of 20% blasts, as the percentage of bone marrow total or non-erythroid cells, or as the percentage of peripheral blood cells. This cut-off point is also currently used in under-resourced laboratories in which the FAB classification is more commonly used.This cut-off point seems to be universally accepted, and for the time being represents the bestknown criterion for defining acute leukemia; however, "arbitrary" may still precede the criterion due to the follow:1. This percentage does not represent a specific biological event in the continuum of an increasing blast count, but is merely, to the best to our knowledge, a cut-off point that facilitates relatively clear classification and therapeutic planning. Nonetheless, some high-risk MDS patients with only 10% bone marrow blasts are actively treated. 2. A significant difference in the blast percentage cut-off point between peripheral blood and bone marrow is well established in MDS; RAEB-1 (blast count <5% in peripheral blood and 5%-9% in bone marrow) and RAEB-2 (blast count of 5%-9% in peripheral blood and 10%-19% in bone marrow). In acute leukemia no such differentiation exits. 3. Morphological findings of pathological "clonal" blasts (type II that contain Auer rods, PseudoChédiak-Higashi or other specific inclusions that are not seen in reactive marrow) refer to the diagnosis of RAEB-2 or AML; here again the arbitrary cut-off point of 20% blasts results in a specific diagnosis. 4. The original FAB classification was based for many years on the arbitrary cut-off point of 30% bone marrow blasts and in the past some patients with 20%-29% blasts remained stable for months without chemotherapy. 5. Although there is a general consensus concerning the criterion for identifying myeloblasts as agranular (type I) and granular blasts (types II and III), there is some disagreement concerning their definitions, and in practice it may be a matter of convention (subjective method) to differentiate them from the continuum of cells, such as determining whether the cell is a type III blast or a promyelocyte. 6. Blasts refer to myeloblasts, lymphoblasts, monoblasts, promonocytes, and megakaryoblasts.

Pattern of hematological malignancies diagnosed by peripheral smear examination

“…8 This 20% blasts cut-off point seems to be universally accepted and for the time being, it represents the best known tool for defining acute leukemia. 9 CML is often suspected on the basis of a complete blood count which shows increased granulocytes of all types, typically including mature myeloid cells. Basophils and eosinophils are almost universally increased.…”

Diagnosis of Acute Leukemia in Under-Resourced Laboratories

“…This 20% myeloblasts cut-off point seems to be universally accepted and for the time being it represents the best known tool for defining acute leukemia. However, the word "arbitrary" may still precede it and this may be attributed to (Abdulsalam, 2011): 1. This precise percent does not represent some specific biological event in the continuum of increasing blast count, but it is merely, to the best to our current knowledge, a cut-off point that permits a relatively clear classification and therapeutic aim.…”

“…Therefore, the era of 20% blasts to diagnose acute leukemia may not stand the time any longer than that of the old FAB group 30% blasts lower threshold. However, at least in the present and the near future the morphology will remain the initial diagnostic test of acute leukemia and the abovementioned blast threshold will still be useful as a tool for classification (Abdulsalam, 2011). The presence or absence of myeloblasts has a central role in diagnosis of AML and suspicion of ALL respectively.…”

“…In order to correctly reference this scholarly work, feel free to copy and paste the following: Abbas H. Abdulsalam (2011). Diagnosis of Acute Leukemia in Under-Resourced Laboratories, Acute Leukemia -The Scientist's Perspective and Challenge, Prof. Mariastefania Antica (Ed.…”