Comment on: McClung JA, Naseer N, Saleem M et al (2005) Circulating endothelial cells are elevated in patients with type 2 diabetes mellitus independently of HbA₁c. Diabetologia 48:345–350

To the Editor: We read with interest the article by McClung et al [1] on circulating endothelial cells in type 2 diabetes mellitus. Despite the exciting and original rationale of the study, we think that some methodological matters somehow weaken the results:

• 1. The small number of control subjects, lower than half of the number of patients.

• 2. As can be judged by the patients' characteristics table, more than half of the patients should also have hypertension and some of them hyperlipidaemia, compared with only one control subject. How can someone exclude the effect of long-standing, even well controlled, hypertension and hyperlipidaemia on the endothelium?

• 3. It does not seem clear that the circulating endothelial cells were elevated in patients due to diabetes alone, since no correlation was observed between circulating endothelial cells and HbA₁c, despite their occurrence in patients with glucose levels ranging from 8.33 to 16.66 mmol/l. If the number of circulating endothelial cells, as a result of endothelial cells sloughing, is not related to the severity of hyperglycaemia, it is difficult to associate this mechanism, at least directly, to the vascular complications of diabetes.

Nevertheless, the findings McClung and co-workers are interesting and surely deserve further study to elucidate the association between circulating endothelial cells and vascular disease in diabetes.