Screening for beta thalassaemia and HbE traits with the mean red cell volume in pregnant women.

Both beta thalassaemia and HbE disease are microcytic red cell disorders. Pregnancy however induces macrocytosis which makes screening with the mean cell volume (MCV) difficult in antenatal patients. In addition, population screening for HbE has not been widely reported in the literature and the screening criteria for beta thalassaemia may not necessarily apply. A study of the value of the MCV for routine screening for both beta thalassaemia and HbE traits in 3696 antenatal patients of different gestational ages was carried out. All patients with an MCV < or = 80 fL received confirmatory tests for haemoglobinopathies. The MCV rose by only 2.0% in pregnancy. A total of 494 patients (13.4% of the general population) had an MCV < or = 80 fL. Of these microcytic patients, 11.3% (56) and 4.7% (23) were eventually confirmed to have beta thalassaemia and HbE traits respectively. The mean MCV for the 3696 antenatal patients was 87.8 fL (SD 7.5) compared to patients with beta thalassaemia and HbE traits, which were 67.5 fL (SD 4.5) and 75.7 fL (SD 4.1). HbE traits were less microcytic than beta thalassaemia traits and overlapped significantly with the general population. Beta thalassaemia trait and HbE trait detected by this screening method constituted 1.52% and 0.62% respectively of the total antenatal population screened. The MCV remains a valid screening parameter in pregnancy for beta thalassaemia trait. As for HbE trait, applying a discriminant value of 80 fL to the MCV in the population screening would miss a significant proportion of the HbE traits.(ABSTRACT TRUNCATED AT 250 WORDS)