Assessment of the Usefulness of Red Cell Indices as a Screening Tool in Haemoglobin E Trait: A Cross Sectional Study

Abstract

Background: HamoglobinE (HbE) is the second commonest structural haemoglobin variant and results from mutation in the β globin gene causing substitution of glutamic acid for lysine at position 26 of the β globin chain. When coinherited with β Thalassemia it becomes a major health burden. Objective: To assess the effectiveness of red cell parameters as a screening tool to identify haemoglobin E traits and to develop a score using red cell parameters which help to identify Haemoglobin E traits in population screening. Materials and methods: The study was carried out on 25 Haemoglobin E trait and 25 controls between 20 to 64 years of age. In all the participants’ full blood count analysis and Haemoglobin variant analysis were done. Participants were selected after excluding all factors which affect red cell indices such as iron deficiency, vitamin B12 and folate deficiency, pregnancy, liver disease, hypothyroidism, chronic alcohol consumption, Diabetes mellitus, Metformin treatment and recent blood transfusion. Comparative analysis of all haematological parameters done between two groups separately for males and females. Results: For cases of Haemoglobin E traits the overall mean Haemoglobin A was 67.9 ± 6.4%, Haemoglobin E 27.3 ± 3.7%, Haemoglobin F 0.3 ± 1.1%, Haemoglobin A2 2.6 ± 3.1%, RCC 5.03 ± 0.89 × 1012/L, Haemoglobin 12.6 ± 1.9 g/dl, MCV 77.4 ± 9.4 fl, MCH 25.4 ± 3.9 pg, MCHC 32.9 ± 2.1 g/dl, RDW 14.21 ± 4%. Between Haemoglobin E traits and normal controls following haematological parameters showed statistically significant difference. Haemoglobin E (p = 4.83 × 10-53), Haemoglobin A (p = 2.61 × 10-41), Haemoglobin F (p = 0.01), Haemoglobin (p = 0.042), Red cell count (p = 0.001), MCV (p = 4.890 × 10-12), MCH (p = 5.5 x 10-13), RDW (p = 0.007). Haemoglobin E percentage showed statistically significant positive correlation with following red cell parameters. Hb E and Red cell count (r = 0.445, t test 0.001), Hb E and Red cell distribution width (r = 0.345, t test 0.014). Haemoglobin E percentage showed statistically significant negative correlation with following indices. Hb E and MCV (r = (-) 0.76, t test 0.000) Hb E and MCH (r = (-)719, t test 0.000). Correlation of Haemoglobin E percentage with MCHC and Haemoglobin were not statistically significant (r = (-) 0.251, t test 0.078) and (r = (-)0.116, t test 0.424). In addition Hb E percentage negatively correlated with Hb A percentage (r = (-)0.917, t test 0.000) and positively correlated with Hb A2 percentage (r = 0.286, t test 0.044), and Hb F percentage (r = 0.366, t test 0.009). Sensitivity of a score as above to select patients for screening, using a cut off score of 2 or above for females and a score of 3 or above for males was 84%. Specificity was 100%. This is higher than if using the current criteria. If people with red cell count > 5 × 1012/L were also selected sensitivity would increase up to 84%, and negative predictive value to 86%. Conclusion: Even when MCV and MCH are normal, people should be screened to exclude haemoglobin E hetrozygosity, if red cell count or RDW is higher than the reference range for the age. Furthermore, clinicians can apply a score as defined above and select patients for screening. Therefore a screening tool using red cell parameters would be cost effective in hospital settings as well as for mass screening programmes.