The I<sup>2</sup> for the pooled AUC analysis indicated generally low to moderate heterogeneity across studies.<h4>Conclusions</h4>The current WHO cut-offs to define anaemia among children are in the middle to upper range of Hb values that best discriminate concurrent physical activity and development, and are in the lower range of values that best discriminate subsequent child development. The gene discussed is GSTM1; the disease is anemia (phenotype).