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Functional Blood Chemistry Manual



Laboratory reference range: 65–99 mg/dL

Functional reference range: 75–85 mg/dL



Glucose is a monosaccharide sugar with the molecular formula C6H12O6. Glucose is the primary energy source of most living cells across the five kingdoms of living organisms. The molecule is a substrate for energy production via aerobic respiration, anaerobic respiration, and fermentation.1 Glucose may be obtained from the diet directly, or more commonly, from the breakdown of disaccharides (e.g., sucrose, lactose) and larger carbohydrates (e.g., starch) consumed in the diet. In gluconeogenesis, glucose can be synthesized from non-carbohydrate precursors such as lactate and pyruvate.1 Glucose may also be converted into glycogen, which is a large, branched polymer of glucose molecules.2 Glycogen is stored in the liver and is available to rapidly release glucose into the bloodstream when needed.

Glucose levels in the bloodstream are hormonally regulated by insulin and, to a lesser extent, by glucagon.3 Circulating glucose, which increases after a meal, is taken up by pancreatic beta cells via glucose transporters.4 In response, these pancreatic beta cells release insulin into the bloodstream. Initially, there is a rapid burst of insulin that reaches a peak within three to five minutes and then subsides within 10 minutes.5 Additional insulin is released by the pancreas if glucose levels in the blood remain elevated.3 Circulating insulin then binds to cells throughout the body, permitting cellular uptake of glucose. As glucose enters the cells, levels drop in the bloodstream. If circulating glucose levels drop too low, glucagon and epinephrine stimulate cells in the liver to breakdown glycogen molecules to form glucose.6 In healthy individuals, these opposing hormones keep circulating glucose levels within normal limits.

An elevated glucose level is called hyperglycemia. Healthy individuals have transient increases in blood glucose, but because of tight hormonal regulation, these levels usually do not exceed 200 mg/dL.7 Hyperglycemia often occurs in the context of diabetes mellitus. The main types of diabetes mellitus are type 1, type 2, and gestational diabetes, though there are several less common varieties. Hyperglycemia may occur in people who do not have a diagnosis of diabetes, but even in these cases, the affected person most likely has some degree of insulin insensitivity or insulin deficiency. Infection and various drugs that cause increases in circulating blood glucose are more likely to affect people with diabetes or prediabetes.8,9 Hyperglycemia may be caused by various endocrine system disturbances, such as Cushing syndrome or hyperthyroidism.8 Diseases that affect the exocrine function of the pancreas, such as pancreatitis and cystic fibrosis, can also cause hyperglycemia.8

Hypoglycemia indicates an abnormally low blood glucose level. As with hyperglycemia, hypoglycemia is more likely to occur in individuals with diabetes, especially those individuals who have poorly controlled diabetes or “brittle” diabetes, which is prone to rapid blood glucose fluctuations.10 Insulin and several classes of oral type 2 diabetes medications are associated with hypoglycemia. Moreover, various prescription medications can cause hypoglycemia, usually in people with diabetes.11 Hypoglycemia may indicate a primary endocrine disorder other than diabetes, such as glucagon deficiency, pheochromocytoma, or Addison’s disease. Starvation and malnutrition may overcome the body’s ability to provide glucose from glycogen stores, which can cause hypoglycemia.

Handheld blood glucose meters can provide rapid and reasonably accurate blood glucose measurements at the bedside.12 Glucose is measured as part of the basic metabolic panel or complete metabolic panel.



High in:8,9,13

  • Diabetes mellitus
    • Type 1
    • Type 2
    • Gestational
    • Latent autoimmune diabetes in adults
    • Maturity onset diabetes of the young
    • Neonatal
  • Genetic defects in insulin action (e.g., type A insulin resistance)
  • Diseases of the exocrine pancreas (e.g., pancreatitis, cystic fibrosis)
  • Endocrinopathies (e.g., acromegaly, Cushing syndrome, hyperthyroidism)
  • Infections (e.g., cytomegalovirus, rubella)
  • Drugs
    • Antibiotics (e.g., quinolones)
    • Atypical antipsychotics (e.g., clozapine, olanzapine)
    • Beta-blockers (e.g., metoprolol, propranolol)
    • Corticosteroids
    • Calcineurin inhibitors (e.g., cyclosporine, tacrolimus)
    • Protease inhibitors
    • Thiazide diuretics


Low in:11,14,15

  • Diabetes mellitus
  • Liver disease
  • Endocrine disorders (e.g., glucagon deficiency, Addison’s disease)
  • Malnutrition
  • Alcohol abuse
  • Substance abuse
  • Jamaican vomiting sickness
  • Gastric surgery
  • Excessive muscular activity
  • Diarrhea (childhood)
  • Drugs
    • Antibiotics (e.g., quinolones, chloramphenicol, pentamidine)
    • ACE inhibitors (e.g., enalapril, lisinopril)
    • Beta-blockers (e.g., metoprolol, propranolol)
    • Salicylates (e.g., aspirin)
    • Diabetes treatments
      • Insulin
      • Sulfonylureas
      • DPP-4 inhibitors
      • SGLT2 inhibitors
      • Alpha-glucosidase inhibitors
    • Chloroquine
    • Clofibrate
    • Disopyramide



High in:

  • Early stages of impaired glucose tolerance and insulin resistance
  • Active stress response

Low in:

  • Reactive hypoglycemia
  • Hypoglycemia (may still be present when glucose is above 65)
  • Impaired liver function



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