Objective

Impaired awareness of hypoglycaemia (IAH) is a major risk factor for severe hypoglycaemia in Type 1 diabetes. Although biochemical hypoglycaemia is asserted to be more frequent in IAH, this has not been estimated accurately. The aim of this study was to use Continuous Glucose Monitoring (CGM) to quantify hypoglycaemia in IAH and evaluate its use in identifying impaired awareness of hypoglycaemia.

Methods

Ninety-five patients with Type 1 diabetes were classified as having normal (n = 74) or impaired awareness (n = 21) using an established method of assessing hypoglycaemia awareness. Hypoglycaemia exposure was assessed prospectively over 9-12 months using weekly 4-point capillary home blood glucose monitoring (HBGM), 5 days of CGM and prospective reporting of severe hypoglycaemia. The frequencies of biochemical and severe hypoglycaemia were compared in patients with normal and impaired awareness of hypoglycaemia.

Results

Patients with impaired awareness had a 3-fold higher incidence of severe hypoglycaemia than those with normal awareness [incidence rate ratio (IRR) 3.37 (95% CI 1.30-8.7); P = 0.01] and 1.6-fold higher incidence of hypoglycaemia on weekly HBGM [IRR 1.63 (95% CI 1.09-2.44); P = 0.02]. No significant differences were observed with CGM [IRR for sensor glucose < or = 3.0 mmol/l 1.47 (95% CI 0.91-2.39); P = 0.12; IRR for sensor glucose < or = 2.2 mmol/l 1.23 (95% CI 0.76-1.98); P = 0.40].

Conclusions

Patients with Type 1 diabetes with impaired awareness had a 3-fold higher risk of severe hypoglycaemia and 1.6-fold higher incidence of biochemical hypoglycaemia measured with weekly glucose monitoring compared with normal awareness, but 5 days of CGM did not differentiate those with impaired from those with normal awareness.