Increased erythrocytic diphosphoglycerate in megaloblastic anaemia. A compensatory mechanism?

The levels of erythrocytic 2,3-diphosphoglyceric acid (2,3-DPG) in a group of patients with megaloblastic anaemia were compared with levels in an iron-deficient subject. The megaloblastic cells appeared to have 2 mumol more 2,3-DPG per g Hb than the iron-deficient cells, at the average haemoglobin level found in the megaloblastic group. The anticipated adaptive decrease in the oxygen affinity of the blood was not apparent when the relationship of P50 (7,4) to haemoglobin level was examined. This was shown to be due to a decreased mean corpuscular haemoglobin concentration (MCHC), which counteracted the effect of the increased 2,3-DPG.