Hypoglycaemia in Clinical Diabetes

54 FREQUENCY, CAUSES AND RISK FACTORSProspective studiesProspective studies offer the potential to provide more convincing data on frequency of mildhypoglycaemia, but substantial differences in prevalence were again reported. In an earlierstudy of 441 patients with type 1 diabetes, managed principally with a twice daily insulinregimen containing soluble and isophane insulins, the weekly average was 1.8 episodes ofmild symptomatic hypoglycaemia (Pramming et al., 1991). These patients had moderateglycaemic control and the period of assessment was one week. This study may be of lessrelevance today in view of the current use of intensive insulin therapy and insulin analogues,yet it is interesting that the rate of mild hypoglycaemia is unchanged today.A Danish prospective study (Pedersen-Bjergaard et al., 2003a) included patients withsimilar characteristics to those in two retrospective studies by the same group (Pedersen-Bjergaard et al., 2001; Pedersen-Bjergaard et al., 2004). Hypoglycaemia was recordedmonthly with episodes of mild symptomatic hypoglycaemia being reported for the precedingweek. Mild hypoglycaemia occurred on average 1.7 times per patient per week. Subjectswere also asked to perform a monthly five-point blood glucose profile and to record in additionany blood glucose value below 3.0 mmol/l. Measurements demonstrating biochemicalhypoglycaemia represented 3.7% of all blood glucose readings.In a community-based study in Tayside, Scotland, 94 adults with type 1 diabetes wereselected at random from a regional diabetes database and were asked to record episodes ofhypoglycaemia prospectively over one month (Donnelly et al., 2005). Their median age was40 years, median duration of diabetes was 18 years and median HbA 1c was 8.3%. Biphasicinsulin was used by 35% of participants and 49% used a combination of intermediate andshort-acting insulins (although the frequency of injections was not reported). A total of325 episodes of mild hypoglycaemia occurred, representing a rate of 41.5 episodes perperson per year, i.e., approximately half the rate reported by Pramming et al., (1991) andPedersen-Bjergaard et al., (2003a). The study has weaknesses; it was relatively small anddata on frequency of blood glucose monitoring were limited. The precise criteria for definingmild hypoglycaemia were not clearly described and, in particular, the role of contemporaneousmonitoring data was not specified. Nevertheless, the subjects were probably veryrepresentative of the population of people with type 1 diabetes in that region.Similar data have been reported from a multicentre study from the United Kingdom (UKHypoglycaemia Study Group, 2007). The primary aim of this study was to compare thefrequencies of hypoglycaemia in individuals with different types and durations of diabetes,receiving different treatment modalities. As part of the study, 50 adults with type 1 diabetesof duration less than five years and 57 adults with type 1 diabetes of greater than 15 yearsduration were recruited. All subjects used two or more injections of insulin per day andtheir glycaemic control was good (mean HbA 1c < 80%). The participants were followed forbetween 9–12 months (mean 10 months) and were asked to report all episodes of symptomatic,self-treated hypoglycaemia and episodes where blood glucose was less 3.0 mmol/l,regardless of symptomatology. Subjects were given forms to record such episodes and wereencouraged to record contemporaneous blood glucose levels. To maximise compliance,subjects were asked to send in completed forms every month to the local research centre,including when no episodes of hypoglycaemia had occurred. If no forms were received,telephone contact was made with the subjects. Using this robust methodology, mean ratesof hypoglycaemia of 35 and 29 episodes per person per year were reported for the shortand long duration groups respectively. The distribution of episodes was much skewed, with