1. Sialic acid moieties of erythrocyte membrane glycoproteins are the principal determinants of the negative charge on the cell surface. The resultant electrostatic repulsion between the cells reduces erythrocyte aggregation and hence the low shear rate viscosity and yield stress of blood.

2. Using g.c.–m.s., a decrease in sialic acid content has been observed in the major erythrocyte membrane glycoprotein, glycophorin A, obtained from nine diabetic patients compared with that from seven normal control subjects [median (range): 3.30 (0.01–11.90) versus 18.60 (3.20–32.60) μg/100 μg of protein, P<0.02].

3. Erythrocyte aggregation, measured by viscometry as the ratio of suspension viscosity to supernatant viscosity (Ls/S) in fibrinogen solution, was increased in ten diabetic patients compared with ten normal control subjects (mean ± sem, 37.6 ± 1.3 versus 33.8 ± 0.6, P<0.02).

4. In the patients in whom both viscometry and carbohydrate analysis were performed, the decrease in erythrocyte glycophorin sialylation and the increase in erythrocyte aggregation in fibrinogen solution were related statistically(LS/S correlated negatively with glycophorin sialic acid content, r = 0.73, P <0.05).

5. Decreased glycophorin sialylation provides an explanation at the molecular level for increased erythrocyte aggregation and it may be important in the pathogenesis of vascular disease in diabetes.

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