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Hypoglycemia in Patients without Diabetes Mellitus:
Evaluation and Management
Rhett Nichols, DVM, DACVIM (SAIM)

Antech Diagnostics, Farmingdale, NY, USA

Hypoglycemia is defined as a blood glucose concentra­ gluconeogenesis. The whole process of gluconeogene­
tion of <60 mg/dL (3.3 mmol/L). Because of the effective­ sis is quite complex and is dependent on certain
ness of defense mechanisms against falling glucose substrates such as amino acids and free fatty acids
concentrations, hypoglycemia is an uncommon clinical mobilized from muscle and adipose tissue. In addition,
event in nondiabetic adult dogs and cats, although two a normally functioning endocrine system is also
exceptions are xylitol toxicity and babesiosis caused by necessary to maintain glucose homeostasis and prevent
Babesia canis rossi in the dog. However, hypoglycemia hypoglycemia. Insulin is the dominant glucose‐lower­
does occur with regularity in neonates, toy and minia­ ing hormone. It suppresses endogenous glucose
ture breed dogs less than 6 months of age without porto­ production and stimulates glucose utilization. The glu­
systemic vascular anomalies (PSVA), and young dogs cose‐raising or counterregulatory hormones include
with PSVA. In addition, hypoglycemia is a very common epinephrine, glucagon, growth hormone (GH), and
complication in insulin‐treated diabetic dogs and cats; cortisol. These increase hepatic glucose production by
the incidence of owner‐reported “occasional” hypoglyce­ stimulating glycogenolysis and gluconeogenesis and
mic episodes ranges from 35% to 40%. Although animals also inhibit glucose utilization by tissues.
with diabetes are not spared the risk for the same hypo­ Because the brain cannot synthesize glucose, store gly­
glycemic disorders as those without diabetes, the vast cogen, or use physiologic circulating concentrations of
majority of their hypoglycemic episodes are the result of alternative fuels effectively, maintenance of brain func­
diabetes treatment. Furthermore, because the patho­ tion, and ultimately survival, requires a continuous sup­
physiology of hypoglycemia in diabetes is distinct, and ply of glucose from the circulation. That, in turn, requires
the diagnostic and management approaches are different maintenance of the plasma glucose concentration within
for pets without diabetes, this chapter will only address the physiological range because blood‐to‐brain glucose
the evaluation and management of hypoglycemia in transport is a direct function of the arterial plasma glu­
patients without diabetes mellitus. In addition, insulin‐ cose concentration. Glucose counterregulatory mecha­
secreting pancreatic endocrine tumors, more commonly nisms effectively prevent or rapidly correct hypoglycemia.
known as insulinomas, will be covered in Chapter XX. These critical physiologic defenses include a decrease in
insulin secretion as glucose levels decline within the
physiologic range; an increase in glucagon secretion; or,
Maintenance of Normal Glucose in its absence, an increase in epinephrine secretion, both
Concentrations in Healthy Dogs and Cats occurring as glucose levels decline just below the physi­
ologic range. In addition, increased cortisol and GH
Cell function and metabolism are dependent on energy secretion are involved in the defense against prolonged
sources delivered via the circulation. There are two hypoglycemia. If these defense mechanisms fail, blood
major sources of energy: meals (ingested carbohydrates, glucose levels will continue to fall, and as a result, insulin
proteins, and fat) and glucose that is produced by the secretion is virtually completely suppressed at glucose
liver. The liver initially produces glucose by the break­ levels <60 mg/mL.
down of stored glycogen (glycogenolysis). As glycogen In essence, hypoglycemia develops when the sum of
stores are depleted, glucose levels are augmented by glucose utilization from the circulation (largely by the

Clinical Small Animal Internal Medicine Volume I, First Edition. Edited by David S. Bruyette.
© 2020 John Wiley & Sons, Inc. Published 2020 by John Wiley & Sons, Inc.
Companion website: www.wiley.com/go/bruyette/clinical