Impedance & Optical Platelet Count Methods & Microcytosis

Difference between impedance and optical platelet count methods in patients with microcytosis of red blood cells

R. PINKOWSKI

Platelet counts (PLT) were conducted in 30 patients diagnosed with microcytosis due to iron deficiency anemia and 30 normal subjects using optical and impedance methods (PLTo and PLTi) in an Abbott Cell-Dyn 4000 analyzer. To achieve the best estimation of the platelet and red blood cell quantity and quality (including platelet aggregation, platelet satellitism, microcytes, and schistocytes), a stained preparation was estimated and platelet count was carried out with the microscopic chamber method (PLTh). When both automated methods were used, result reproducibility was better than with the manual method. Correlation of the platelet counts between the methods was high (r > 0.98), and highest for PLTo and PLTh (r = 0.997). When the impedance method was used, platelet counts were higher on average than when the optical method was used and differed, in absolute values, by 34.1x109/L (9.7%) (p < 0.001). In some cases, the differences between PLTi and PLTo were bigger, even exceeding 150x109/L (>30%). The difference between PLTi and PLTo had an inverse correlation with mean corpuscular volume (MCV) (r = -0.635). Samples from normal subjects did not demonstrate the above discrepancies or a similar relationship with MCV. The platelet volume histogram is helpful for evaluating the interference of microcytes and platelets estimated using the impedance method. The optical method yields more reliable results in the patients with microcytosis. PLTi estimation in cases of microcytosis is insufficient, and its results are not always reliable.

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