GCG

Glucagon

Hormones

What is Glucagon?

Glucagon is a 29-amino acid peptide hormone produced by alpha cells of the pancreatic islets of Langerhans. It is the primary counter-regulatory hormone to insulin, functioning to raise blood glucose levels when they fall too low. While insulin promotes glucose uptake and storage, glucagon stimulates hepatic glycogenolysis (breakdown of stored glycogen into glucose), gluconeogenesis (production of new glucose from amino acids and other substrates), and ketogenesis. Together, insulin and glucagon maintain blood glucose within a narrow physiological range.

Glucagon secretion is stimulated by low blood glucose, amino acids (particularly alanine and arginine), catecholamines, and sympathetic nervous system activation. It is suppressed by high blood glucose, insulin, somatostatin, and GLP-1. In healthy individuals, the insulin-to-glucagon ratio determines the metabolic state: a high ratio (fed state) promotes anabolism and glucose storage, while a low ratio (fasting state) promotes catabolism and glucose release. Dysregulation of glucagon signaling contributes to hyperglycemia in diabetes mellitus.

Why It Matters

Glucagon dysregulation is increasingly recognized as a key contributor to diabetes pathophysiology—type 2 diabetes involves not just insulin deficiency or resistance but also relative glucagon excess that drives hepatic glucose output. This "bihormonal" model has led to therapeutic advances including GLP-1 receptor agonists and dual GIP/GLP-1 agonists that suppress glucagon. Glucagon is also clinically important as a life-saving emergency treatment for severe hypoglycemia and as a tumor marker for rare glucagonomas. Understanding glucagon physiology is essential for comprehending metabolic regulation.

Normal Reference Ranges

GroupRangeUnit
Fasting Adults50–150pg/mL

Reference ranges may vary by laboratory. Always compare results to the ranges provided by your testing facility.

What High GCG Levels Mean

Common Causes

  • Glucagonoma (rare pancreatic alpha-cell tumor)
  • Type 2 diabetes mellitus (relative hyperglucagonemia)
  • Diabetic ketoacidosis
  • Acute pancreatitis
  • Chronic kidney disease (reduced clearance)
  • Cirrhosis
  • Prolonged fasting or starvation
  • Stress, trauma, or sepsis

Possible Symptoms

  • Necrolytic migratory erythema—characteristic painful, blistering skin rash (glucagonoma)
  • Severe weight loss
  • Diabetes or glucose intolerance
  • Deep vein thrombosis (glucagonoma is strongly thrombogenic)
  • Anemia
  • Glossitis and stomatitis (sore, red tongue and mouth)
  • Depression

What to do: Markedly elevated fasting glucagon (>500 pg/mL) with the characteristic rash (necrolytic migratory erythema) is virtually diagnostic of glucagonoma—the "4D syndrome" of dermatitis, diabetes, DVT, and depression. CT or MRI of the pancreas is used for localization. Glucagonomas are often large and malignant at diagnosis, with liver metastases in 50–80% of cases. Surgical resection is the primary treatment when feasible. Somatostatin analogs (octreotide) can control symptoms and glucagon secretion. Moderately elevated glucagon in diabetes reflects the bihormonal pathophysiology and is addressed by medications that suppress glucagon (GLP-1 agonists, DPP-4 inhibitors).

What Low GCG Levels Mean

Common Causes

  • Chronic pancreatitis with islet cell destruction
  • Total or near-total pancreatectomy
  • Cystic fibrosis-related pancreatic insufficiency
  • Somatostatin-producing tumors (somatostatinomas)
  • Idiopathic (rare)

Possible Symptoms

  • Recurrent or severe hypoglycemia (especially fasting)
  • Impaired counter-regulatory response to low blood sugar
  • Symptoms of hypoglycemia: shakiness, sweating, confusion, seizures
  • Difficulty maintaining blood glucose during illness or fasting

What to do: Glucagon deficiency impairs the counter-regulatory response to hypoglycemia, putting patients at risk for severe low blood sugar. In patients with diabetes who also have pancreatic insufficiency, the loss of glucagon makes hypoglycemia management more challenging. Treatment focuses on preventing hypoglycemia through careful insulin dosing, frequent meals, and patient education about recognizing and treating low blood sugar. Patients with impaired glucagon response should carry emergency glucose sources. Exogenous glucagon (injectable or nasal) should be available for emergencies but does not replace the continuous counter-regulatory function.

When Is GCG Testing Recommended?

  • When a glucagonoma is suspected (characteristic rash, unexplained diabetes, DVT)
  • When evaluating recurrent hypoglycemia with impaired counter-regulation
  • When assessing pancreatic endocrine function in chronic pancreatitis
  • As part of research protocols studying diabetes pathophysiology

Frequently Asked Questions

Glucagon and insulin are opposing hormones that maintain blood glucose homeostasis through a tightly coordinated balance. After eating, rising blood glucose stimulates insulin release from beta cells and suppresses glucagon from alpha cells—this promotes glucose uptake into muscle and fat, glycogen synthesis, and lipogenesis. During fasting, falling glucose suppresses insulin and stimulates glucagon—this promotes glycogen breakdown, gluconeogenesis, and fat mobilization to maintain fuel supply. The insulin-to-glucagon ratio, rather than either hormone alone, determines the metabolic direction. In type 2 diabetes, this coordination is disrupted: alpha cells fail to suppress glucagon appropriately after meals, contributing to postprandial hyperglycemia.
A glucagonoma is an extremely rare neuroendocrine tumor of the pancreatic alpha cells, with an incidence of approximately 1 in 20 million people per year. It typically presents with the "glucagonoma syndrome": necrolytic migratory erythema (a distinctive painful, crusting skin rash that migrates across the body), new-onset diabetes or worsening glucose control, deep vein thrombosis, weight loss, anemia, and depression. The rash is often the presenting feature and may be misdiagnosed for months to years before the tumor is identified. Glucagonomas are usually found in the body or tail of the pancreas and are malignant in approximately 60–80% of cases. Fasting glucagon levels >500 pg/mL are highly suggestive, and levels >1000 pg/mL are virtually diagnostic.
Glucagon is a life-saving emergency treatment for severe hypoglycemia when a person is unconscious or unable to take oral glucose. It works by stimulating the liver to release stored glycogen as glucose, typically raising blood sugar within 10–15 minutes. Glucagon is available as an intramuscular injection kit (requiring reconstitution), a pre-filled auto-injector (dasiglucagon), and a nasal powder that can be administered by bystanders without injection. It is essential for people with type 1 diabetes and those on insulin therapy. Glucagon has limited effectiveness in patients with depleted glycogen stores (prolonged fasting, alcohol use, advanced liver disease) because it depends on hepatic glycogen for its glucose-raising effect.

Related Biomarkers

InsulinInsulinGLUGlucoseHbA1cHemoglobin A1c

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Medical Disclaimer: This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Reference ranges may vary between laboratories. Always consult your healthcare provider for interpretation of your specific test results.

Disclaimer: SymptomGPT is not a medical diagnosis tool and does not provide medical advice. Always consult a qualified healthcare professional. If you are experiencing a medical emergency, call 911 immediately.