Alinity hq platelet count is not impacted by severe microcytosis

BACKGROUND: Impedance technology has been shown to overestimate platelet (PLT) count in samples with microcytes, while the optical‐fluorescence PLT count (PLT‐F) by Sysmex has been suggested to be unaffected by microcytosis. The Abbott Alinity hq analyzer employs multi‐dimensional optical PLT counting. Our goal was to assess the accuracy of this technology in microcytic samples. METHODS: Platelet measurements were performed by Alinity hq and the impedance (PLT‐I) and PLT‐F methods on a Sysmex XN‐3000 analyzer on 464 samples. PLT concentration range was 6.56–947 × 10(9)/L and mean cell volume (MCV) 40.9–123.0 fL. Samples were categorized into normocytic (MCV > 80 fL), microcytic (MCV 65–80 fL), and severely microcytic (MCV < 65 fL) groups. RESULTS: Alinity hq PLT count showed excellent agreement with PLT‐F (r = 1.00). Sysmex PLT‐I data showed somewhat weaker correlation with both PLT‐F and Alinity hq (r = 0.98). Increasing bias between Sysmex PLT‐I and PLT‐F was seen with decreasing MCV values, with mean bias of 35.2 × 10(9)/L in severe microcytosis. An inverse relationship was demonstrated between the PLT‐I versus PLT‐F bias and MCV (p < 0.0001). Consistent mean bias was observed between Alinity hq and PLT‐F across all MCV ranges. Mean platelet volume was suppressed or flagged by Sysmex XN in 50% of the samples in the severely microcytic group, and markedly higher red cell distribution width (RDW) was reported compared to Alinity hq (18.1% vs 13.7%, p < 0.0001). CONCLUSION: The Sysmex PLT‐I method overestimated the PLT count in samples with severe microcytosis. Alinity hq provided PLT counts and PLT and RBC indices that were not impacted by microcytosis.