Alinity hq platelet count is not impacted by severe microcytosis

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.

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 × 10⁹ /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.

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 × 10⁹ /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).

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.