Hypoglycemia is the condition of low blood glucose concentration (< 3.9 mmol/L or < 70 mg/dL, per the American Diabetes Association and the Endocrine Society) that may be caused by endocrine deficiencies or genetic mutations, severe illness, glycogen storage disorders, reactive subtotal gastrectomy, or nonislet cell tumors (Doege-Potter syndrome is a rare nonislet cell paraneoplastic syndrome associated with a benign or malignant fibrous tumor of the chest). Drug-induced hypoglycemia is common (related to insulin therapy, angiotensin converting enzyme [ACE] inhibitors, alcohol, antidiabetic drugs such as sulfonylureas and glinides, beta blockers, insulin-like growth factor 1, quinolones, certain antifungals, and certain antimalarials). Hypoglycemia may also be caused by hyperinsulinism (insulinoma), extended fasting, malnutrition, malabsorption, or insulin autoimmune syndrome. It is most common in individuals with diabetes mellitus type 1 and is considered the most frequent and serious adverse effect of insulin therapy.

Risk factors for hypoglycemia in adults include inadequate patient education, changes in caloric intake (enteral or parenteral), improper timing of insulin with meals, decreased renal or hepatic clearance, tapering of steroids, acute illness dementia, and advanced age (older than 65 years).

In neonates, hypoglycemia may be related to endocrine deficiencies; low birth size; delayed first feeding; severe renal, liver, or heart disease; sepsis; or hereditary fructose intolerance.

Signs and symptoms depend on the causes but may be adrenergic (including agitation, tremor, hunger, weakness, palpitation, nausea, irritability, sweating, and tachycardia) or neuroglycopenic (including confusion, lethargy, paresthesia, blurred vision, headache, dizziness, behavioral changes, seizures, loss of consciousness, and coma). An infant may present with irritability, poor feeding, tachypnea, cyanosis, hypothermia, or lethargy within a few hours after birth.