Background: The accuracy of automated platelet counts can be compromised when measuringrnseverely thrombocytopenic samples. This is especially of concern because current clinicalrnguidelines lowered the prophylactic platelet transfusion threshold to 10 Ã— 109/L for patientsrnwithout additional risk factors. This count is a threshold for background count of manyrnhematological analyzers, thus making validation of the automated platelet count a crucial step.rnObjective: To compare manual platelet estimates and automated platelet count by Sysmex KXrn21N at Tikur Anbessa Hospital (TASH).rnMethods: A hospital based cross-sectional comparative study was conducted in Tikur AnbessarnSpecialized Hospital from January to March 2017 on 320 blood samples. Platelet count wasrnenumerated by sysmex KX 21 and by manual method. Number of platelets/1000 RBC in PBSrnwas multiplied by automated RBC count in 106/uL to get an estimate of platelet count in 103/uLrnand the average number of platelet/10 oil emersion field (OIF) was multiplied by 20,000. Therndata were entered and analyzed using SPSS version 20 and interpreted accordingly. Statisticalrnsignificance was determined at 95% confidence interval. Pearson correlation coefficient wasrnused to determine correlation between the methods. Bland Altman plot was used to assessrnagreement between tests. Figures and tables were used for the description of the data.rnResult: For normal platelet count the Paired t-test showed non-significant difference betweenrnautomated and PLT estimated from average platelets/10 OIF (p>0.05), were positively correlatedrn(r=0.994) and in the limit of agreement range (95%). For severe thrombocytopenic samples therntwo platelet estimation methods did not show significant difference when tested by paired t-testrn(p>0.05), were positively correlated (r=0.869) and in the limit of agreement range (97.5%).rnConclusions: The mean PLT count by automated and PLT estimated from PLT:RBC ratio forrnnormal count did not show significant difference so the two methods could give the same PLTrncount result. The mean PLT count for severe thrombocytopenic patient samples did not showrnsignificant difference when analyzed by the two manual platelet estimation methods.rnKey words: Peripheral blood smear, Platelet count, Platelet: red blood cell ratio, plateletrnestimate