Frequency of symptomatic and asymptomatic hypoglycaemia in Type 1 diabetes: effect of impaired awareness of hypoglycaemia

Abstract

To characterize the frequency and the nature (symptomatic vs. asymptomatic) of hypoglycaemia in people with Type 1 diabetes with impaired awareness of hypoglycaemia. A group of 19 patients with Type 1 diabetes with normal hypoglycaemia awareness were matched for age, sex, duration of diabetes and glycaemic control with 19 patients with impaired awareness of hypoglycaemia. Frequency of severe hypoglycaemia in the preceding year was estimated retrospectively. Capillary blood glucose was monitored prospectively four times daily, over a 4-week period. All blood glucose values < 3 mmol/l were recorded and classified by symptom response. The patients with impaired awareness of hypoglycaemia exhibited twice the frequency of all episodes of hypoglycaemia over the 4-week monitoring period than those with normal awareness (mean ±sd 7.9 ± 5.4 vs. 3.7 ± 3.6, P = 0.003). No differences between the two subgroups were observed in the total number of symptomatic hypoglycaemia episodes (4.2 ± 3.3 vs. 3.2 ± 3.4, P = 0.25). The group with impaired awareness of hypoglycaemia had a sevenfold higher incidence of asymptomatic hypoglycaemia than those with normal awareness (3.7 ± 5.3 vs. 0.5 ± 1.2, P = 0.001); these episodes comprised 47% of all glucose values < 3.0 mmol/l in this group, compared with 14% in the normal awareness group. The annual prevalence of severe hypoglycaemia for patients with impaired awareness of hypoglycaemia was 53% compared with 5% for patients with normal awareness, and these patients had a significantly higher incidence of severe events (1.6 ± 2.8 vs. 0.1 ± 0.3, P = 0.001). Adults with Type 1 diabetes who have impaired awareness of hypoglycaemia are exposed to a much higher incidence of asymptomatic hypoglycaemia than those with normal awareness and are at higher risk of developing severe hypoglycaemia.