Objectives Haemorheological variables influence endothelial function through the release of several factors. Clinical studies have described an association among blood viscosity, haematocrit, haemoglobin and macro-angiopathy. Few data are reported about the association between haemorheological variables and micro-angiopathy. The aim of the present study was to evaluate the association between these variables and retinopathy in subjects with type 2 diabetes.

Methods 111 men, 79 postmenopausal women, and 95 healthy age- and sex-matched controls were recruited. Haematocrit and haemoglobin were measured by standard methods. Blood viscosity was calculated according to the formula (0.12× haematocrit)+(0.17× (plasma proteins−2.07)). Subjects were grouped according to the presence or absence of diabetic retinopathy, while the severity of retinopathy was classified according to the Early Treatment Diabetic Retinopathy Study scale.

Results Haemoglobin, haematocrit and whole blood viscosity were significantly lower in subjects with retinopathy compared to subjects without retinopathy in both sexes. These variables significantly decreased with increasing severity of retinopathy. A multiple logistic regression analysis confirmed the independent inverse association among viscosity, haematocrit, haemoglobin and retinopathy (p<0.01).

Conclusion Results demonstrate the association among low viscosity, haemoglobin, haematocrit and diabetic retinopathy. The mechanisms responsible for this association can be hypothesised. Reduced haemoglobin might cause direct organ damage. Low blood viscosity, through the reduction of shear stress, might inhibit the anti-atherogenic functions of endothelial cells.