• Iron
• deficiency
• diagnosis
• mean
• corpuscular
• haemoglobin

As recently as 2006, to the exclusion of any mention of mean corpuscular haemoglobin (MCH), mean corpuscular volume (MCV) was the sole parameter selected for triggering evaluation of iron status in patients with microcytic anaemia.1 This strategy was, arguably, attributable to the advice emanating from the WHO guideline Assessing the Iron Status of Populations, which recommended MCV as an indicator of iron deficiency on the basis of the fact that ‘MCV indicates whether RBCs are smaller than usual (microcytic) which is a common sign of iron deficiency anaemia…’.2 Accordingly, the observation that ‘the MCH (mean corpuscular haemoglobin) rather than mean corpuscular volume (MCV) has become the most important red cell marker for detecting ID (iron deficiency) in circulating red blood cells’3 deserves to be more fully referenced than was the case in the excellent review of disorders of iron metabolism.3 Nevertheless, it should also be acknowledged that, in many instances, iron deficiency anaemia is both microcytic and hypochromic,4 notwithstanding the fact that hypochromia may antedate the onset of microcytosis.5–8 It was in the retrospective evaluation of 69 subjects with serum ferritin <20 ng/ml that low MCH values (<27 pg) were first documented as being superior to low MCV values (<77 fl) in predicting serum ferritin …