Development of internal quality control and proficiency testing program for thalassemia screening at Lamplaimat Hospital, Burirum province

Abstract

Thalassemia screening using a combined osmotic fragility (OF) test and dichlorophenolindophenol (DCIP) precipitation test has been implemented in Lamplaimat Hospital since 2005. However, quality control (QC) system has not yet been established. In order to develop an internal QC and proficiency testing program for thalassemia screening, one of laboratory staffs was assigned to prepare QC samples by selecting left-over blood samples from routine practice. The selection criterion for positive QC was MCV < 75 fl and Hb > 10 g/dl. For negative QC, sample with MCV > 85 fl and Hb > 12 g/dl was selected. These QC samples were firstly tested using the OF and DCIP tests by the assigned staff and then blindly tested by the other two laboratory staffs who took responsibility on the OF/DCIP screening in routine practice. The screening results were recorded as unknown samples. From January to June 2009, a total of 100 QC samples (66 positive QC and 34 negative QC) were collected. All of them were sent to the Centre for Research and Development of Medical Diagnostic Laboratories, Faculty of Associated Medical Sciences, Khon Kaen University, to investigate for thalassemia and hemoglobinopathies using standard methods. Agreement of the OF/DCIP screening between the 2 staffs was evaluated using Kappa statistics.  Acceptable proficiency testing was assessed according to the criteria of no false negative OF result in a-thalassemia 1 or b-thalassemia carrier and no false negative DCIP result in Hb E carrier with Hb E > 25% and with false positive rate of less than 20 % in normal QC samples (sample without a-thalassemia 1, b-thalassemia and Hb E). Based on Kappa analysis, a perfect agreement was obtained for both OF test (K = 0.93) and DCIP test (K = 0.96). Proficiency testing on thalassemia screening of the two staffs revealed acceptable result. The data indicates the same standard in performing thalassemia screening of the Lamplaimat’s laboratory staffs. The internal QC and proficiency testing program established in this study should prove useful for effective prevention and control of thalassemia in the region.