Fig. 1

Ability of zinc protoporphyrin-haem ratio, either alone or in combination with haemoglobin concentration, to discriminate between children with and without iron deficiency. Panel a: Receiver operating characteristics (ROC) curves for various blood markers, used alone, to discriminate between iron-deficient and iron-replete children. Panel b: As in Panel a, with haemoglobin concentration and whole blood ZPP, alone and in combination. Panel c: As in Panel a, with haemoglobin concentration and erythrocyte ZPP, alone and in combination. Panel d: As in Panel a, with combined haemoglobin concentration and whole blood ZPP, versus combined haemoglobin concentration and erythrocyte ZPP. Hb: haemoglobin concentration. Grey diagonal lines in ROC curves indicate a ‘worst’ possible test, which has no discriminatory value and an area-under-the-curve (AUC) of 0.5. An ideal marker would have a curve that runs from the lower-left via the upper-left to the upper-right corner, yielding an AUC of 1.0