Objectives Hypochromia and microcytosis exist in iron deficiency anaemia (IDA) and thalassaemias. Several red blood cell (RBC) indices have been proposed to differentiate between these conditions, but with low specificity or sensitivity confirmation by standard laboratory methods is still required, especially in adults. In addition, most studies originated in countries with a higher prevalence of IDA or beta thalassaemias. As, in the United Arab Emirates, alpha thalassaemias prevails (with diagnosis beyond infancy requiring DNA studies not widely available), we studied the value of RBC indices to diagnosis IDA in our population.

Methods In a cohort study of 91 children (6 months to 12 years) with either microcytosis (MCV <77 fl) or hypochromia (MCHC <32 g/dL), with or without anaemia, we calculated the RBC indices from the full blood count at presentation. We analysed their predictive value as well as their respective Youden’s index for the diagnosis of IDA.

Results IDA occurred in 18.7%. Alpha thalassaemia traits occurred in 73% of the other children, beta thalassaemia traits in 20% and beta thalassaemia in 4%. The Youden’s index shows that the best discriminatory indices for IDA are, in descending order: a Green-King index >65 (correctly identifies 72.5% of cases), red cell distribution with (RDW)>14 (identifies 55%) and a positive England-Fraser index (identifies 47%).

Conclusion In countries with a high prevalence of alpha thalassaemia, IDA in children with microcytosis is best differentiated with a Green-King index >65, a RDW>14 and a positive England Fraser index.