Frequent Inaccuracies in the Sysmex XN-Series Immature Granulocyte Percentage (IG%) among HIV Positive Patients and those on Treatment for Acute Lymphoblastic Leukaemia in Samples Flagged for Smear Review

Background: The immature granulocyte percentage (IG%) generated by Sysmex XN-Series analysers can reduce the need for manual differential counting in samples with significant left shift. In this study, we assessed the accuracy of this parameter in comparison to light microscopy in the South African setting.  

Results: A manual differential count was performed on 153 samples submitted for a routine differential white cell count with an IG% count >2% that were flagged for smear review. IG% results compared well in the majority of samples, but were grossly discordant in 26 patients (17%) (mean analyser IG% 10.3% vs mean manual IG% 1.7%). Patient factors identified to contribute to erroneous results included treatment of acute lymphoblastic leukaemia with chemotherapy and underlying HIV- infection. This was attributable to the miscounting of neutrophils that occurred particularly in patients with bizarre neutrophil morphology. This anomaly is frequently observed in HIV-positive patients.  

Conclusion: Raised IG% results should be treated with some circumspection in areas with high HIV-seropositivity rates.