Assessment of reduced awareness of hypoglycaemia

Journal of Diabetes Nursing, April, 2003 by David Kerr, Joan D Everett

Introduction

Unfortunately, some patients with diabetes lose the ability to detect impending hypoglycaemia. This article describes the mechanisms involved and how reduced awareness of hypoglycaemia can be assessed. We used a validated method to evaluate the extent of the problem of reduced awareness of impending hypoglycaemia within a clinic-based population and compared these rates with those perceived by healthcare professionals.

KEY WORDS

* Hypoglycaemia

* Reduced awareness

* Warning symptoms

* Healthcare professionals

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The brain is almost entirely dependent upon a continuous supply of glucose from the peripheral circulation for normal function. Therefore, complex physiological mechanisms have evolved in order to protect cerebral glucose supply. As blood glucose levels fall towards 4mmol/l, there is activation of the autonomic nervous system with release of counter-regulatory hormones. At a blood glucose level of around 3.5mmol/L, characteristic warning symptoms (sweating, shaking, lightheadedness, hunger) alert individuals to take appropriate action by eating rapidlyabsorbed carbohydrate. Below 3mmol/L, impairment of higher cerebral (cognitive) function develops and below this, the patient is at risk of marked neuroglycopaenia with altered consciousness, seizures or coma. (Hepburn et al, 1991).

Unawareness of hypoglycaemia

Unfortunately, loss of ability to detect the early onset of hypoglycaemia occurs in up to 25% of patients with long-standing type 1 diabetes. (Pramming et al, 1991). This unawareness of hypoglycaemia can take three forms: reduction in intensity or complete loss of warning symptoms; failure to recognise the warning symptoms as indicators of low blood glucose levels; or failure to take appropriate action despite recognising symptoms.

Unawareness of hypoglycaemia is also associated with:

* Intensive insulin therapy

* Attempts to achieve normoglycaemia

* Sleep

* Alcohol

* Recurrent hypoglycaemia per se

* Extremes of age

* Renal failure.

Loss of warning symptoms can be compounded by the effects of low blood glucose on memory (Deary, 1999); patient self-reported rates could be an underestimate due to amnesia for the event.

Establishing loss of warning symptoms

Healthcare professionals involved in diabetes care are responsibile for determining whether patients are prone to recurrent, unheralded hypoglycaemia particularly with respect, for example, to being able to drive a motor vehicle.

There are three accepted methods of assessing awareness of hypoglycaemia:

1) Self report questionnaires

2) Determination of impaired awareness on the basis of actual recognition occurring over a period of time, e.g. using a hand-held computer, where blood glucose levels are recorded as well as hypoglycaemic symptoms experienced (Cox et al, 1995).

3) Experimentally induced hypoglycaemia by defining the glycaemic threshold for the occurrence of autonomic symptoms.

One study concluded that questionnaire assessment of hypoglycaemia awareness (Clarke et al, 1995) agreed reasonably well with laboratory-based physiological assessment (Janssen et al, 2000).

Aim

The aim of this study was to evaluate the extent of the problem of reduced awareness of impending hypoglycaemia within a clinic-based population and compare actual rates with those perceived by health professionals.

Methods

Patients

100 consecutive patients (55 men) with type I diabetes (mean age 51, range 17-88 years; duration of diabetes 21, range 1-53 years, with an HbA[.sub.lc] of 8.5, SE [+ or -] 0.2%) and 100 consecutive patients (51 men) with type 2 diabetes (age 66, range 38-83 years; duration of diabetes 12, range 3-30 years with a mean HBA[.sub.lc] of 8.7 [+ or -] 0.3%) attending the diabetes clinic were asked to complete a validated questionnaire (Clarke et al, 1995).

The questionnaire consisted of eight questions that patients answered by ticking boxes. The patients were asked about the frequency of severe hypoglycaemia during the last 6 months, how low their blood glucose levels had to drop before they had symptoms of hypoglycaemia and how often low blood glucose levels were recorded without any symptoms. Each of the eight questions was either scored as awareness or reduced awareness of hypoglycaemia. Four or more responses of reduced awareness signified that the patient had reduced awareness of hypoglycaemia. All data were analysed using SPSS.

Healthcare professionals

50 healthcare professionals, from the Wessex region who were working in diabetes care, were randomly selected and asked:

* What proportion of patients with type 1 diabetes have reduced awareness of hypoglycaemia?

* Does this reduced awareness vary with the prevailing standard of control?

Results

Patients with type 1 diabetes

Table 1 shows the characteristics of patients with type I diabetes. Patients on multiple daily injections (MDI) of soluble insulin were older (53 [+ or -] 3 versus 46 [+ or -] 2 years, p<0.046) and had a longer duration of diabetes (30 [+ or -] 3 versus 19 [+ or -] 2 years, p<0.002) than those on MDI of an analogue insulin. Patients using a fixed mixture of insulin were older (62 [+ or -] 3 versus 53 [+ or -] 3 years, p<0.043) but had a shorter duration of diabetes (14 [+ or -] 3 versus 30 [+ or -] 3, p<0.001) compared with those on MDI of soluble insulin.

After analysing the questionnaires, all patients were either labelled as having awareness or reduced awareness of hypoglycaemia.