Hypoglycaemia in Clinical Diabetes

FREQUENCY OF HYPOGLYCAEMIA 55some individuals reporting no events and others in excess of 200 per year; overall, approximately85% of individuals experienced at least one episode of mild hypoglycaemia. Theauthors did not report the relative proportion of symptomatic and asymptomatic episodes, orthe proportion of symptomatic episodes with a corroborative blood test, but these data areextremely informative and indicate that duration of diabetes has little impact on the frequencyof mild hypoglycaemia, an observation that has been made before (Pedersen-Bjergaardet al., 2004).In a 12 month prospective study of 243 insulin-treated adults, Leckie and colleaguesreported that mild, symptomatic hypoglycaemia occurred with a frequency of only eightepisodes per patient per year (Leckie et al., 2005). This is one of the lowest rates to bereported in a large group of people, most of whom had type 1 diabetes. However, severalreasons may account for this result. The subjects had suboptimal glycaemic control, with amean HbA 1c of 9.1%. A small number of people with insulin-treated type 2 diabetes wereincluded, who might be expected to have had a lower overall frequency of hypoglycaemia.The prevalence of impaired awareness of hypoglycaemia, a recognised risk factor for hypoglycaemia(see Chapter 7), was exceptionally low in this cohort at 3%. The proportion ofsubjects using insulin analogues was not reported, but it would certainly have been higherthan in studies from the early 1990s. The main strength of the study, namely a long periodof follow up, may have been an inadvertent weakness by causing ‘patient fatigue’, i.e.,participants may have been less assiduous in recording episodes of mild hypoglycaemia asthe study progressed. Finally, this was primarily a study of the impact of hypoglycaemiaoccurring in the work place. Thus, all of the participants were in full-time employment and sorepresented an atypical group of individuals who may have adopted strategies to reduce thefrequency of hypoglycaemia because of the potentially adverse effects that this could haveon their jobs.Frequency of Asymptomatic, Biochemical HypoglycaemiaAside from the problem of specifying a biochemical threshold for hypoglycaemia, therecan be little doubt that asymptomatic hypoglycaemia is even more common than symptomatic,mild hypoglycaemia. However, a major determinant of the frequency of documentedasymptomatic hypoglycaemia is, necessarily, the frequency with which blood glucose ismeasured.Traditionally, two different approaches have been used to investigate this phenomenon:(a) taking multiple sequential blood samples in a controlled, experimental setting, over a prespecifiedtime period; and (b) inviting patients in the community to perform capillary bloodtests at multiple, pre-set time points. Providing the sampling frame is sufficiently frequent,the advantage of the former strategy is that it will capture all episodes of biochemicalhypoglycaemia, however brief, during the time period under study. The disadvantage isthat it is labour intensive for investigators and so only a small number of subjects can bestudied over a relatively short time period, such as 12 or 24 hours. By contrast, the use ofhome blood glucose monitoring, particularly with meters that store the results electronically,allows larger numbers of subjects to be studied over very prolonged time periods. Typically,subjects are asked to perform periodic seven-point profiles, i.e., blood glucose estimationsbefore each meal, two hours after food and during the night. The obvious disadvantages ofthis mode of investigation are that subjects may forget to perform the relevant monitoring,