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

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.

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.

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.

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.