Hypoglycaemia

Hypoglycaemia describes the situation of an abnormally low plasma glucose concentration.

It may be defined biochemically as a plasma glucose of less than 2.5 mmol/l (although the threshold for symptoms is variable); note that a BM stix estimation may be subject to user error and it is always wiser to obtain a lab estimation.

The Diabetes Audit and Research in Tayside, Scotland (DARTS) study of 367,501 people, 8655 of whom had diabetes, identified a total of 244 episodes of severe hypoglycaemia in 160 patients (1)

• overall prevalence was 7.1% in patients with type 1 diabetes and 7.3% in patients with type 2 diabetes treated with insulin, compared with 0.8% in patients with type 2 diabetes treated with an oral sulfonylurea

Notes:

• as plasma glucose levels decrease in people without diabetes, various physiological consequences occur. At levels of 4.2 mmol/L endogenous insulin secretion is suppressed (2)
  • at approximate levels of 3.7 mmol/L, increased glucagon, adrenaline, cortisol and growth hormone secretion occur
  • when levels of 3.1 mmol/L are reached, autonomic symptoms appear. Cognitive dysfunction occurs at levels of approximately 2.5 mmol/L
  • levels vary greatly between individuals and can be affected by the antecedent glucose control in any individual
    
    
• people with diabetes, the severity of hypoglycaemia is defined based on the clinical manifestations of the episodes
  
  • a level of less than 4.0 mmol/L is suggested for definition of hypoglycaemia in patients treated with insulin or an insulin secretagogue (2)

• hypoglycaemia unawareness occurs when the threshold for autonomic warning symptoms to appear becomes lower than the threshold for the neuroglycopenic symptoms, so that the first signs of hypoglycaemia will often be confusion or loss of consciousness
  • attenuated epinephrine response to hypoglycaemia in type 1 diabetes is a marker of an attenuated autonomic, sympathetic neural as well as adrenomedullary response that causes the clinical syndrome of hypoglycaemia unawareness-loss of the warning, largely neurogenic symptoms of developing hypoglycaemia (3)
    • because it compromises behavioural defences against developing hypoglycaemia (e.g., the ingestion of food), hypoglycaemia unawareness is also associated with a high frequency of severe iatrogenic hypoglycaemia
• asymptomatic hypoglycaemia is the presence of a biochemically low glucose level without any symptom
  
  
• American Diabetes Association (4) classification of hypoglycaemia:
  • Level 1 - glucose <70 mg/dL (3.9 mmol/L) and >= 54 mg/dL (3.0 mmol/L)
  • Level 2 - glucose <54 mg/dL (3.0 mmol/L)
  • Level 3 - a severe event characterized by altered mental and/or physical status requiring assistance for treatment of hypoglycaemia

References:

1. Leese GP et al.Frequency of severe hypoglycemia requiring emergency treatment in type 1 and type 2 diabetes: a population-based study of health service resource use. Diabetes Care. 2003 Apr;26(4):1176-80.
2. Yale JF et al.Canadian Diabetes Association clinical practice guidelines for the prevention and management of hypoglycemia in diabetes. Canadian Journal of Diabetes Care 2001.
3. Cryer PE, Davis SN, Shamoon H. Hypoglycemia in diabetes. Diabetes Care. 2003 Jun;26(6):1902-12
4. American Diabetes Association (ADA). Glycemic Targets: Standards of Medical Care in Diabetes-2021. Diabetes Care 2021 Jan; 44(Supplement 1): S73-S84