Performance evaluation of the white cell precursor channel on the Sysmex XN hematology analyzer in HIV specimens

Background: Automated hematology analyzers generate white blood cell (WBC) suspect flags to indicate smears requiring manual review. In a human immunodeficiency virus (HIV) patient population with a high frequency of abnormal specimens, the usefulness of these flags depends on their sensitivity and specificity. The white cell precursor (WPC) channel on the Sysmex XN-9000 analyzer (Sysmex Corporation, Kobe, Japan) has recently been introduced in order to distinguish immature cells such as blasts and abnormal lymphocytes. Methods: The efficiency of the flags generated by WPC reflex testing was compared to the white cell differential (WDF) on the Sysmex XN-9000 in 400 routine HIV samples. Results: A flag was generated by the WDF channel in 346 (86.50%) samples. Addition of the WPC to the WDF resulted in a 20.99% reduction in the smear review rate. WPC analysis correctly identified the initial WDF flag in 59 (60.82%) samples with 'blasts?' or 'abnormal lympho?' flags. WPC showed an excellent sensitivity of 100%. However, the specificity remained poor. On investigation, samples with chronic infection/ inflammation (35.00%) and lymphopenia (63.25%) were associated with a high false positive rate of 76.32% and 55.56%, respectively. WPC analysis removed 45 (51.72%) coexisting 'atypical lympho?' false positive WDF flags. The 'atypical lympho?' flag showed an increased sensitivity and specificity of 88.46% and 74.67%, respectively. Conclusion: White cell precursor reflex testing showed improved flagging efficiency for the 'atypical lympho?' flag, which was a good indicator of reactive lymphocytes during chronic infection/inflammation. Nevertheless, the false positive rate for 'abnormal lympho/blasts?' was high in the presence of lymphopenia and infection.