Do infections cause hyperglycemia in patients with diabetes or other risk factors for elevated blood glucose?

Do Infections Increase Glucose?

Yes, infections cause hyperglycemia through stress-induced metabolic changes that increase hepatic glucose production and induce insulin resistance, even in patients without pre-existing diabetes. 1

Mechanisms of Infection-Induced Hyperglycemia

Acute illness triggers a cascade of metabolic and hormonal changes that directly elevate blood glucose levels. During infection, the body increases hepatic glucose production through both gluconeogenesis and glycogenolysis, despite elevated serum insulin levels, indicating profound insulin resistance. 1 This occurs through upregulation of counter-regulatory hormones including glucagon, cortisol, growth hormone, catecholamines, and inflammatory cytokines, all of which stimulate glucose production and impair peripheral insulin-mediated glucose uptake. 1

The metabolic shift during infection redirects glucose to immune cells to support aerobic glycolysis in the early stages of fighting infection. 1 This phenomenon is often termed "stress diabetes" or "diabetes of injury." 1

Clinical Significance and Prevalence

Hyperglycemia during acute illness is extremely common and clinically significant. Approximately two-thirds of patients with acute illness develop elevated serum glucose, even without pre-existing diabetes. 1 This stress-induced hyperglycemia is independently associated with:

• Increased mortality and morbidity 1
• Longer hospital stays and higher healthcare costs 1
• Higher infection rates, particularly in surgical patients 2
• Delayed wound healing 2

Bidirectional Relationship: Infection and Glucose

The relationship between infection and hyperglycemia is bidirectional and creates a vicious cycle. 2

Infection Causes Hyperglycemia:

• Influenza infection increases abnormal glucose levels by 75% in patients with type 2 diabetes 2
• Sepsis commonly causes disturbances in glucose homeostasis 2
• Acute illness can precipitate diabetic ketoacidosis in susceptible patients 2

Hyperglycemia Worsens Infections:

• Elevated glucose provides energy substrate for bacterial proliferation 3, 4
• Hyperglycemia impairs neutrophil function, including migration, phagocytosis, and microbial killing 5
• High glucose concentrations decrease formation of neutrophil extracellular traps 5
• Hyperglycemia promotes bacterial virulence, tissue adherence, and biofilm formation 4

Monitoring Recommendations

Check blood glucose levels in every patient with sepsis or acute infection whenever possible. 2 This is particularly critical in patients with:

• Altered mental state (86% specificity for predicting hypoglycemia in septic patients) 2
• Known diabetes or metabolic syndrome 2
• Age >60 years 2
• Previous history of transitory hyperglycemia 2

Target Glucose Levels During Infection

Maintain blood glucose between 70-180 mg/dL (4-10 mmol/L) during acute infection. 2

• Lower threshold: Keep glucose ≥70 mg/dL (≥4 mmol/L) to prevent hypoglycemia 2
• Upper threshold: Avoid targeting tight control <150 mg/dL (<8.3 mmol/L) due to increased risk of dangerous hypoglycemic events 2
• In diabetic patients: Mortality increases when glucose exceeds 180 mg/dL (10 mmol/L) 2
• In non-diabetic patients: Mortality increases when glucose exceeds 140 mg/dL (7.8 mmol/L) 2

Common Pitfalls

Beware of hypoglycemia in specific infection contexts. Certain infections (particularly malaria) and sepsis in late stages can cause hypoglycemia, especially in malnourished patients, children, or those with liver disease. 2 If blood glucose cannot be measured in a patient with impaired mental state, presume hypoglycemia and administer 30-50g of intravenous glucose. 2

Stress hyperglycemia in non-diabetics may be more dangerous than similar glucose levels in known diabetics. At the same glucose level, stress-induced hyperglycemia in previously non-diabetic patients carries worse prognosis than chronic hyperglycemia in known diabetics. 2