Abstract: Objective: To investigate the diagnostic value of changes of leukocyte count in patients with acute myocardial infarction(AMI).Methods: A total of 47 patients with AMI were selected according to the following standards:the chest pain lasted for no more than 2 hours,the myoglobin(Mb) was negative,and no one had diseases related to inflammation.The blood samples were obtained respectively at the time of onset,4-8 h and 12-24 h after the chest pain.And the leukocyte-reactive protein,cardiac troponin I(cTNI) and Mb were detected.All the patients were followed up for 3-12 months.During this period,their WBC was examined for three times,and the mean value was compared with that of the autoleukocyte controls as well as that of the normal control.Results: Within 2 hours of the onset of chest pain and with the Mb still negative,the leukocyte count in the AMI patients began to rise(9.12±2.18) ×10⁹/L,which was higher than that of the autoleukocyte controls(6.49±1.09) ×10⁹/L and the normal control(5.97±1.24) ×10⁹/L(P<0.01).But neutrophil percentage presented no significant difference between AMI patients and the autoleukocyte controls at the time of onset(P>0.05).There was no significant difference in C reactive protein(CRP) levels between AMI patients and the normal control at the time of onset(P>0.05).The levels of WBC and CRP in AMI patients increased significantly after Mb and cTNI became positive(P<0.01),and reached their peak at 12-24 hours after the onset of chest pain.At the same time neutrophil percentage increased significantly,too(P<0.01).Conclusions: The white cell count begins to rise significantly at the onset of acute myocardial infarction when the Mb and cTNI are still negative.So the increase of leukocyte count is one of the early symptoms of AMI.