Effects of Hyperglycemia on Blood Sugar Levels
Hyperglycemia, by definition, is an elevated blood glucose level above the normal range, typically greater than 180 mg/dL (10 mmol/L), which occurs when glucose influx exceeds glucose outflow from the plasma compartment. 1
Pathophysiological Mechanisms
Hyperglycemia develops through several key mechanisms:
Reduced insulin action: Hyperglycemia results from a reduction in the net effective action of circulating insulin coupled with elevated counterregulatory hormones (glucagon, catecholamines, cortisol, growth hormone) 1
Increased glucose production: In the fasting state, hyperglycemia is directly related to increased hepatic glucose production 1
Impaired glucose utilization: Defective insulin stimulation of glucose disposal in target tissues, mainly skeletal muscle, contributes to hyperglycemia 1
Renal threshold exceedance: When blood glucose levels exceed the renal threshold (approximately 180 mg/dL for most individuals), glycosuria occurs, which partially but insufficiently curbs further hyperglycemia 1, 2
Physiological Consequences of Hyperglycemia
Persistent hyperglycemia leads to several adverse physiological effects:
Osmotic diuresis: Glycosuria leads to osmotic diuresis with loss of water, sodium, potassium, and other electrolytes 1
Dehydration: Significant fluid losses occur due to osmotic diuresis, leading to dehydration 1
Metabolic derangements: In diabetic ketoacidosis (DKA), hyperglycemia is accompanied by lipolysis and ketone body formation, leading to metabolic acidosis 1
Impaired immune function: Hyperglycemia causes impairment of host defenses, including decreased polymorphonuclear leukocyte mobilization, chemotaxis, and phagocytic activity 3
Worsening insulin resistance: Short-term hyperglycemia can reduce glucose uptake, creating a vicious cycle that further worsens hyperglycemia 4
Clinical Manifestations
Hyperglycemia manifests through various symptoms:
Classic symptoms: Polyuria, polydipsia, polyphagia, weight loss, and blurred vision 2
Acute complications: In severe cases, hyperglycemia can progress to hyperglycemic crises such as DKA or hyperosmolar hyperglycemic state (HHS) 1
Neurological effects: Progressive clouding of sensoria and eventually coma may occur in severe hyperglycemic states 1
Impact on Morbidity and Mortality
Hyperglycemia significantly affects patient outcomes:
Hospital mortality: Hyperglycemia is associated with increased in-hospital mortality, especially in critically ill patients 1
Infection risk: Patients with hyperglycemia have significantly higher infection rates, particularly in surgical settings 1, 3
Length of stay: Hyperglycemic patients typically require longer hospital stays and are more likely to need ICU care 1
Cardiovascular outcomes: A significant relationship exists between blood glucose levels and mortality in acute myocardial infarction 1
Management Considerations
The approach to hyperglycemia should focus on:
Blood glucose monitoring: Regular monitoring with self-monitoring of blood glucose (SMBG) is essential for managing hyperglycemia 1
Insulin therapy: For hospitalized patients with persistent hyperglycemia, basal/bolus insulin therapy is recommended to maintain target glucose levels 1
Target glucose levels: In critically ill patients, maintaining blood glucose between 140-180 mg/dL is generally recommended to balance the risks of hyperglycemia against those of hypoglycemia 1
Correction of underlying causes: Identifying and addressing the precipitating factors for hyperglycemia is crucial for effective management 1
Important Caveats
Variable renal threshold: The renal threshold for glucose is highly variable between individuals due to factors including variation in renal glucose transporters, kidney function, and insulin resistance status 2
Risk of hypoglycemia with treatment: Aggressive treatment of hyperglycemia carries the risk of hypoglycemia, which can be equally or more dangerous than moderate hyperglycemia 1
Stress-induced hyperglycemia: Severe illness, trauma, or surgery can cause stress-induced hyperglycemia due to increased counterregulatory hormones, even in patients without diabetes 2
Hyperglycemia should be promptly recognized and treated to prevent both acute complications and long-term adverse outcomes related to persistent elevated blood glucose levels.