Objectives: Materials and methods: Results: Conclusions: This study shows that applying root cause analysis to the problems involved in specimen rejection provided improvement in the process. The collaborative approach has efficiently solved the problems of inappropriate specimen collection.The major errors of specimen rejection were: 1) blood for Coagulogram is clotted; 2) misuse of caps/tubes; 3) blood for CBC is clotted; 4) inappropriate amount of sample. The causes identified from the questionnaires were some misunderstandings of sample collection process. The distribution of the leaflet provided improvement of the sample rejection rate. The sample rejection rate were significantly reduced from 2.05% to 0.99% with p-value (chi-square test) < 0.01.This study reports an investigation to improve the specimen rejection rate using root cause analysis. The records of specimen quality collected during 2005-2006 were analyzed. To determine the causes of the problems, we conducted a questionnaire survey to assess the understanding about specimen rejection criteria for hematology testing from the relevant nurses. The data showed that an instructive leaflet about the collection process was highly required. We then prepared and distributed instructive leaflets for the usage of Complete Blood Count (CBC) and Coagulogram tubes to the ward staffs. The rates of rejection between the 3 months before the distribution of the leaflet and during the 3 months after the distribution (August 2007 - March 2008) were compared.Using root cause analysis to evaluate and improve the specimen collection process in order to reduce the sample rejection rate for hematology testing.