Using red cell indices as a screening test for the detection of haemoglobin E trait in population screening for haemoglobin disorders

Abstract

INTRODUCTION: When screening populations for haemoglobin E trait, which is found in up to 5% in some regions in Sri Lanka, some believe that the full blood count with red cell indices, demonstrating hypochromasia and microcytosis (MCV<80fl and MCH< 27pg), is not sensitive enough, as up to 5% may be missed. If this is true, more complicated and expensive tests will be necessary to detect Hb E trait. There are no studies which have attempted to test the efficacy of red cell indices as a screening test for Hb E trait in Sri Lanka AIMS: To test the sensitivity of the full blood count with red cell indices as a screening test for the detection of haemoglobin E trait MATERIALS AND METHODS: Individuals diagnosed to have Hb E trait by the usage of high performance liquid chromatography (HPLC) - (Bio Rad) had their red cell indices measured using an automated cell counter (Coulter, Act Diff III) RESULTS: 47 Individuals with Hb E trait were identified using HPLC analysis. 28 were females (59%). The haemoglobin levels ranged from 10.5 to 15.4 g/dl. (Mean 12.6). There was only one individual with an MCV of 80, whilst the rest had values below that. MCV values ranged from 58-80fl. There were 3 individuals with an MCH over 27 (27.4, 28.8 and 27.4). The individual with an MCV of 80 had an MCH of 27.4. CONCLUSIONS: In this ongoing study we found that by using a cutoff point for MCV at 80ft up to 2% of individuals with Hb E trait will be missed. As the screening test needs to be more sensitive than this, we suggest that by using a slightly higher cutoff point for the MCV (eg. 81 fl) we would still be able to detect individuals with Hb E trait using red cell indices, thus minimizing cost.