Elsevier

Journal of Diabetes and its Complications

Volume 24, Issue 6, November–December 2010, Pages 392-397
Journal of Diabetes and its Complications

Classification of hypoglycemia awareness in people with type 1 diabetes in clinical practice

https://doi.org/10.1016/j.jdiacomp.2009.07.006Get rights and content

Abstract

Aim

No consensus exists on classification of hypoglycemia awareness. We compared three methods for assessment of hypoglycemia awareness in a clinical setting.

Methods

A questionnaire including the three methods was filled in by 372 outpatients with Type 1 diabetes [43% women, age 51±14 years (mean±S.D.)], duration of diabetes 24±13 years, and hemoglobin A1c 8.2±1.0%). Method A (Diabetes Care, 17, 697–703) and B (Diabetes Care, 18, 517-522) classify into two degrees of awareness, while Method C (Diabetes/Metabolism Research and Reviews, 19, 232-240) includes three classes.

Results

Normal awareness was reported in 75%, 51%, and 41% (A, B, C); 25% and 28% had impaired awareness (A, B); and 13% were unaware (C); 46% belonged to the intermediate class of impaired awareness (C), while 21% were not classifiable (B). Higher rates of severe hypoglycemic events were reported by patients with impaired awareness (A, B) and unawareness (C) compared to aware patients. Patients with impaired awareness (C) had more severe hypoglycemia than aware patients and less severe hypoglycemia than unaware patients. A lower rate of severe hypoglycemia was reported by aware patients classified by Method C than A. Fractions of patients with normal awareness without an event of severe hypoglycemia were 0.81, 0.86, and 0.91 (A, B, C).

Conclusion

All three methods for assessment of hypoglycemia awareness are feasible in clinical practice since the degree of awareness is associated with risk of severe hypoglycemia. The trisected method (C) identifies an intermediate group with impaired awareness and with a risk of severe hypoglycemia that is significantly different from those of aware and unaware patients.

Introduction

A reduced ability to perceive the onset of hypoglycemia — impaired hypoglycemia awareness — is the major known risk indicator for severe hypoglycemia in patients with Type 1 diabetes (Bragd et al., 2003, Clarke et al., 1995, Gold et al., 1994, Hepburn et al., 1994, MacLeod et al., 1993, Mühlhauser et al., 1998, Pedersen-Bjergaard et al., 2003, Pedersen-Bjergaard et al., 2004, ter Braak et al., 2000) and insulin-treated Type 2 diabetes (Akram et al., 2006, Henderson et al., 2003). In most instances, awareness is gradually impaired along the course of diabetes simultaneously with the occurrence of hypoglycemia-associated autonomic failure (Cryer, 2005). The most severe cases of impaired awareness are termed hypoglycemia unawareness. Presence of impaired hypoglycemia awareness is associated with 3- to 10-fold increased risk of severe hypoglycemia in both types of diabetes (Akram et al., 2006, Bragd et al., 2003, Clarke et al., 1995, Gold et al., 1994, Henderson et al., 2003, Hepburn et al., 1994, MacLeod et al., 1993, Mühlhauser et al., 1998, Pedersen-Bjergaard et al., 2003, Pedersen-Bjergaard et al., 2004, ter Braak et al., 2000). It is important to identify patients with impaired hypoglycemia awareness in order to prevent severe hypoglycemic episodes and — equally important — to identify patients with normal hypoglycemia awareness and low risk of severe hypoglycemia because these patients may benefit from stricter glycemic control.

Methods of assessing hypoglycemia awareness for clinical use should ideally provide maximal information about the risk of severe hypoglycemia in the most simple and reliable way. Furthermore, they should reflect the fact that impairment covers a wide spectrum of abnormality, meaning that awareness is not an all-or-none phenomenon. Due to the complexity of hypoglycemia awareness, there is, at present, no general agreement on a classification.

Only three studies validating prospective recording of severe hypoglycemic episodes against self-estimated state of awareness at entry into the study have been published (Clarke et al., 1995, Gold et al., 1994, Pedersen-Bjergaard et al., 2003). Two of the methods divide hypoglycemia awareness into two classes (Clarke et al., 1995, Gold et al., 1994), while the third method includes three classes of hypoglycemia awareness (Pedersen-Bjergaard, Pramming et al., 2003).

We conducted a cross-sectional questionnaire survey comparing the usefulness of these three methods for assessment of self-estimated hypoglycemia awareness in a clinical setting (Clarke et al., 1995, Gold et al., 1994, Pedersen-Bjergaard et al., 2003) in a large cohort of patients with Type 1 diabetes.

Section snippets

Methods

In May 2006, a questionnaire comprising a random combination of all questions from all three methods for classification of hypoglycemia awareness (Clarke et al., 1995, Gold et al., 1994, Pedersen-Bjergaard et al., 2003) was mailed to all patients with Type 1 diabetes in our outpatient diabetes clinic together with a return envelope. Questions were explained in paragraphs so that misunderstandings could be avoided. The patients were requested to contact the clinic in case of doubt of how to fill

Results

A total of 470 patients were invited to participate and 385 patients (82%) returned the questionnaire. Thirteen patients had to be excluded because of missing or incomplete answers, leaving 372 patients (79%) for evaluation. Participants were older and had lower HbA1c levels than nonparticipants but did not otherwise differ (Table 1).

Discussion

The clinical assessment of awareness can be based on four different types of data: (a) subjects' own estimation of their state of awareness, (b) self-monitored glucose data or continuous glucose monitoring data with scoring of symptoms in case of hypoglycemia, (c) an objective measure in terms of the response to a provoked hypoglycemic challenge, (d) an evaluation of the clinical consequence of impaired awareness: occurrence of severe hypoglycemia, or a combination of these methods. A simple

Acknowledgments

The authors thank research nurses Pernille Banck-Petersen and Tove Larsen for skilful data collection.

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