Abstract: Objective:To explore the relationship between PLT parameters and PLT morphology and the application of abnormal PLT index as alarms for manual blood smear review of CBC. Method:588 patients were selected out as our objects,all the samples were tested by PLT-I method by XE-5000 and re-tested by manual blood smear review.The samples were divided them into 3 groups:group A represented samples with MPV<12.0 FL as our control group,group B represented samples with MPV>12.0 FL and group C represented samples with no PLT parameter values.Another 1 000 patients were chosen as our validating objects and tested by XE-5000 and re-tested by manual smear review according to the 41 rules plus alarms that MPV>12 FL or without PLT parameter values.Another 31 PLT aggregating samples were chosen as group D and we summarized the PLT index distribution by XE-5000. Result:The P-LR had a positive relationship with MPV(r=0.7427,t=20.9).The true positive rates of giant PLT of group A,B and C were 0.80%,8.79% and 45.89% respectively and the false negative rates of giant PLT were 0.80%,2.09% and 6.93% respectively if we comprehended the results by XE-5000 according to the 41 rules alone.The FN of giant PLT of C were obviously higher than that of group A(U=22.35,P<0.01).The manual smear review rate of our validating objects increased from 19% to 22.6% and the true positive rate of giant PLT increased from 2.4% to 4.1%.The PLT index of 96.8%(30/31)samples of group D were missed.Conclusion:Samples with MPV>12 FL and samples with no PLT parameter values might indicate the existence of giant PLT or PLT aggregating and 41 rules might not be sufficient to screen out all samples with giant PLT.Therefore,we recommend that samples with abnormal PLT indices should be re-tested by manual smear review no matter whether any of the 41 rules are triggered or not.