Enhanced accuracy of optical platelet counts in microcytic anemia.

OBJECTIVE To determine whether microcytic erythrocytes influence the accuracy of automated platelet (PLT) counting. METHODS We divided a total of 206 K2 ethylenediaminetetraacetic acid (EDTA)-anticoagulated blood samples into 4 groups, as follows: In group 1 (control group), normal mean corpuscular volume (MCV > 80 fL) and PLT count equal or greater than 140,000/microL (n = 45); group 2, normal MCV, reduced PLT count (< 140 x 10(3)/microL, n = 41); group 3, microcytic samples with normal PLT count (n = 68); and group 4, microcytic samples with reduced PLT count (n = 49). We also compared the platelet counting using electroimpedance (PLT-EI), platelet count using fluorescent optical (PLT-FO), and platelet-count manual (PLT-M) methods, using the Sysmex XE 2100 automatic analyzer. RESULTS Despite highly significant overall correlations between PLT-EI and PLT-FO, PLT-EI and PLT-M, and PLT-FO and PLT-M (r = 0.95 [all P < .001]), use of the PLT-EI method resulted in widely overestimated PLT counts in microcytic samples (MCV < 80 fL), compared with use of PLT-FO and PLT-M. Our results identify an MCV of 70 fL as the critical threshold below which PLT-EI became unreliable. CONCLUSION The PLT-EI mode overestimated PLT counts compared with PLT-FO and PLT-M modes in microcytic blood. Therefore, PLT-FO is the preferred method for PLT counting in patients with microcytic anemia when using an automated analyzer.