Real and artefactual erythrocyte swelling in hyperglycaemia

The mean erythrocyte volume of patients with acute diabetic decompensation was determined by Coulter measurement and found to be elevated above normal (mean increase 5.5 mu3). Experiments in vitro revealed this to be an artefact associated with Coulter determination. A more reliable estimate of in vivo erythrocyte volume can be obtained from centrifugated haematocrit and erythrocyte count. With this method, true erythrocyte swelling parallel to glucose concentration was observed when erythrocytes were exposed to isotonic glucose-NaCl solutions. This volume increase resulted from decreased sodium concentration and was in the order of 0.5-1.0 mu3 per mmol/l of sodium. Glucose was osmotically ineffective. Similar volume changes were documented in a diabetic patient parallel to his daily variations of blood glucose. In severe diabetic decompensation, dehydration usually prevents an increase in erythrocyte volume. We conclude that hyperglycaemia is associated with erythrocyte swelling if total serum tonicity remains within the normal range.