True basophilia is an uncommon finding in hematology labs. If a manual count differs from the automated count, it is often due to inexperienced laboratorians identifying neutrophils with toxic granulation as basophils; it has even been my experience that students will sometimes identify small lymphocytes as basophils. However, in this case, the analyzer results were higher than those from the manual differential. The CLSI standard for determining basophil count is to count at least 400 cells (200 each on two smears) because of the low numbers and, thus, the possibility of statistical error. It is unknown in this case whether the manual count was based on 400 cells.
Reactive basophilia is fairly uncommon. When the basophil count exceeds the reference range, the main reason for concern is a myeloproliferative disease such as chronic myeloid leukemia (CML) or sometimes a myelodysplastic syndrome (MDS). It is important to differentiate reactive from malignant.
The situation is that basophil counts can sometimes be spuriously high or low, depending on the hematology analyzer used.
The following pages will review some possible causes of spurious results, summarize reactive and neoplastic causes, and mention how to differentiate the two.
