Comparative Analysis of Impedance and Optical Platelet Counting Techniques in Correlation with Peripheral Smear Examination in Thrombocytopenic Pregnant Women

Abstract

Background: Thrombocytopenia affects 7–12% of pregnant women, which may increase the risk of maternal bleeding. Accurate platelet counting is crucial in obstetrics regarding drugs and transfusion decisions. Impedance and optical-based counting methods are used in automated haematology analyzers. However, their reliability can be affected by large and giant-sized platelets common in pregnancy. Platelet counting on Peripheral smear under light microscope is time-consuming, but it has remained the reference standard for confirming low counts.

Objectives: To assess the correlation between platelet counting by peripheral smear and both the impedance and optical-based methods in thrombocytopenic pregnant women.

Methodology: A prospective cross-sectional study was conducted at Haematology Lab, PIMS Hospital Islamabad on 176 thrombocytopenic pregnant women. Platelet count was measured by peripheral smear examination, impedance and optical methods on the same EDTA sample. Data was analyzed using SPSS v20 with Spearman correlation assessment between the peripheral smear method with both the automated methods. Correlation was also done based on Mean Platelet Volume (MPV) and the degree of thrombocytopenia.

Results: Platelet counting by Peripheral smear examination showed a very strong correlation with optical counts (r=0.96) as compared to impedance (r=0.72, p<0.001). In the cases with higher MPV>12fL, optical correlation was greater than impedance method (r=0.95 vs 0.59, p=0.017). Optical method had a much better correlation as compared to impedance in mild (r=0.91 vs 0.28) and moderate (r=0.75 vs 0.26) thrombocytopenia.

Conclusion: Impedance method is unreliable in thrombocytopenia cases with higher MPV. Optical method is more reliable in mild to moderate thrombocytopenia. In very low platelet count, both methods showed similar results.