General blood tests and leukocyte differential count are very useful in diagnosing, treating and managing patient’s diseases. This study was conducted to reduce errors caused by the manual method as much as possible by using an automated hematology analyzer (Sysmex K-4500), and to alleviate work burden of the laboratory. The T1 and T2 values calculated from leukocyte differential count that was obtained from the automated hematology analyzer Sysmex K-4500, and the results measured from the manual method were compared and analyzed by using the blood samples of 400 patients who were commissioned in the diagnostic laboratory of the hospital with 120 beds. Upon the results of the study, T1 and T2 obtained from lymphocyte differential count of the automated hematology analyzer Sysmex K-4500 demonstrated high correlation compared to manual method, and the analysis of monocyte, eosinophil, basophil and band cell obtained from T1, T2 and manual method enabled percentile calculation, even though it was difficult to predict the exact monocyte, eosinophil, basophil and band cell. Therefore, it is regarded that the optimal patient results can be reported if manual method observation is selectively combined while referring to T1 and T2 obtained from lymphocyte differential count of the automated hematology analyzer Sysmex K-4500.