Appropriate MCV and MCH cut off values for screening of -thalassemia 1 and 0-thalassemia: Study at 4 community hospitals in northeast Thailand

Abstract

Screening of thalassemia carriers in Thailand is usually encountered with a high false positive rate associated with unnecessary workload and expense of confirmatory test. This could be due to the use of inappropriate cut off values for MCV and MCH. In this study, the retrospective MCV and MCH values of samples referred to the Thalassemia Service Unit, Centre for Research & Development of Medical Diagnostic Laboratories, Faculty of Associated medical Sciences, Khon Kaen University during February 2009 – January 2011 for confirmation from 4 community hospitals in northeast Thailand were analyzed. Among 746 samples, 154 were found to carry a – thalassemia 1 or b⁰-thalassemia allele. All of these subjects had MCV < 78 fl and MCH < 25 pg. Using MCV of 78 fl and MCH of 25 pg as the cut off   levels, prospective screening was done at the same hospitals for additional 145 subjects during April – June 2011. No false negative for those of subjects with a – thalassemia 1 or b⁰-thalassemia was observed (n = 21). As compared to the standard cut off levels (MCV 80 fl and MCH 27 pg), it was found that these new cut off levels could lead to a reduction in false positive rate by about 25 % for MCV and 33 % for MCH with no alteration on the sensitivity. The approach used in this study should prove useful for other hospitals to re-analyze their screening data and establish their appropriate cut off levels which should lead to effective prevention and control program of severe thalassemia in the area.