Basophil Differentials as a Marker for Atypical Lymphocyte Morphologic Characteristics

To establish a cutoffpoint for the automated basophil differential at which point smear review becomes essential. We reviewed 184 blood samples for atypical lymphocyte flagging. At the arbitrary basophil cutoffpoints of 0, 0.6%, 1.2%, 1.8%, 2.4%, 3.0%, and 3.6%, we calculated the sensitivity, specificity, negative predictive value (NPV), and positive predictive value (PPV) for atypical lymphocyte flagging. Using this information, we plotted the receiver operating characteristic (ROC) curve. Seventy-nine samples had atypical flagging and a mean basophil differential of 2.086%. In 105 samples with no atypical flagging, the mean basophil differential was 0.750%. The sensitivity, specificity, NPV, and PPV were 73.4%, 81.9%, 80.3%, and 75.3%, respectively at the basophil cutoffpoint of 1.2%; the area under the ROC curve was 0.70. Among samples with no atypical flagging, 2 peripheral smears (with basophil differentials of 1.8% and 3.8%, respectively) also contained reactive lymphocytes. We recommend the automated basophil count of 1.2%, as measured by the ADVIA 2120 analyzer, as the criterion for smear review, which may be used as an independent marker of atypical lymphocyte morphologic manifestations.