Role of red cell distribution width in screening for Hb E trait in population screening for haemoglobin disorders

Abstract

INTRODUCTION AND OBJECTIVES: The national screening policy for haemoglobinopathies uses the red cell indices MCV <80 and MCH<27 as cut offs, a strategy known to miss some individuals with Hb E trait (EBT), the commonest abnormal haemoglobin in Sri Lanka. We investigated the possibility of increasing the accuracy of red cell indices in detecting Hb E trait. Objective was to determine if red cell distribution width (RDW) cut off values would help increase sensitivity of screening for Hb E trait. METHODS: Mean corpuscular volume (MCV), mean corpuscular haemoglobin (MCH) and red cell distribution width (RDW) of all samples referred for thalassaemia screening were measured using the Coulter counter. High Performance Liquid Chromatography (HPLC) was carried out as the gold standard to detect haemoglobinopathies. Receiver Operating Characteristic (ROC) curve was drawn to determine the cut-off value for EBT against Beta trait (BTT) and other anaemias. RESULTS: There were 246 BTT, 110 EBT and 151 other anaemias. Mean (SD) MCV of BTT 62.7 (5.9), EBT 73.4 (7.4) and other anaemias 71.3 (8.3) femtolitres (p<0.001). Mean (SD) MCH of BTT 19.6 (2.1), EBT 24 (2.7) and other anaemias 22.8 (3.6) (p<0.001). Mean (SD) RDW among BTT were 16 (2.8), EBT 14.5 (2.9) and other anaemias 15.8 (4.2) (p<0.001). Using 14.45 as cut off for RDW in addition to accepted cut off values for MCV<80 and MCH<27, gave a predictive sensitivity of 98.2% for EBT. DISCUSSION: By using RDW cutoff at 14.45 in addition to the accepted screening indices, sensitivity of Hb E trait detection went up from 86.6% to 98.2%. This study highlights the importance of taking RDW into consideration for screening.