Feline Hypocalcemia: Low Ionized Calcium, Tetany and Calcium Gluconate Therapy

Feline hypocalcemia is a critical metabolic emergency defined by a subnormal concentration of biologically active ionized calcium in the circulation (iCa < 1.0 mmol/L or < 4.0 mg/dL). Because extracellular calcium stabilizes neuronal and sarcolemmal voltage-gated sodium channels, a precipitous drop lowers depolarization thresholds, igniting spontaneous neuromuscular excitability. Most frequently triggered by iatrogenic parathyroid injury following bilateral thyroidectomy in hyperthyroid cats, acute pancreatitis, or puerperal eclampsia, hypocalcemia escalates from facial twitching into severe generalized tetany and diazepam-refractory seizures requiring continuous ECG-monitored intravenous calcium gluconate administration.

Sources

This guide is not a substitute for a vet.24h Emergency Vets

Veterinary intensive care nurse monitoring a resting cat on a thermal pad with infusion pump — Foto: Nekolife

In this guide

Etiology and Pathomechanisms

Postoperative Hypoparathyroidism: Accidental excision or devascularization of the parathyroid glands during bilateral surgical thyroidectomy represents the primary cause in clinical practice (onset typically 24–72 hours post-surgery).
Acute Necrotizing Pancreatitis: Peripancreatic saponification of mesenteric free fatty acids with circulating calcium ions, precipitating insoluble calcium soaps.
Puerperal Tetany (Eclampsia): Excessive calcium excretion into milk in nursing queens 2–4 weeks postpartum.
Sodium Phosphate Fleet Enemas: Lethal in cats; massive colonic phosphate absorption forces reciprocal calcium precipitation.

Clinical Signs and Progression of Hypocalcemic Tetany

Prodromal Signs: Anxiety, agitation, hypersensitivity to auditory or tactile stimuli, intensive face rubbing with front paws, and dilated pupils.
Fasciculation Stage: Fine muscle twitches of the lips, ears, and periorbital muscles, progressing to generalized stilted gait.
Tetany and Convulsive Seizures: Painful extensor rigidity, generalized muscle tremors, hyperthermia, and tonic-clonic convulsions unresponsive to benzodiazepines.
Cardiac Dysrhythmias: Marked prolongation of the ST segment and QT interval on ECG, carrying high risk of arrest.

Diagnosis and Electrolyte Evaluation

Ionized Calcium (iCa) Testing: Essential because total calcium correlates poorly with physiological status.
Serum Electrolytes and Chemistry: Concurrent assessment of magnesium (hypomagnesemia impairs PTH secretion and action), phosphorus, and renal parameters.

Emergency Medical Protocol

Slow IV Calcium Gluconate (10%): 0.5–1.5 mL/kg diluted 1:1 with sterile saline administered over 15–30 minutes under continuous electrocardiographic (ECG) monitoring. Infusion must pause immediately if bradycardia or arrhythmias appear.
Constant Rate Infusion (CRI): Maintained until oral medications achieve homeostatic intestinal absorption.
Long-Term Oral Maintenance: Active vitamin D metabolites (Calcitriol) combined with elemental oral Calcium carbonate administered with food.

Prognosis

Excellent in transient and postpartum cases; cats with permanent hypoparathyroidism lead normal, healthy lives on maintenance calcitriol and oral calcium with routine monitoring every 3 to 6 months.

Scientific sources and references

Peterson, M. E. et al. (2020). Hypocalcemia in cats: clinical presentation, diagnosis, and management of acute and chronic hypoparathyroidism. Journal of Feline Medicine and Surgery, 22(9), 834-846.
Holowaychuk, M. K. (2021). Hypocalcemia in critical illness in small animals. Veterinary Clinics of North America: Small Animal Practice, 51(3), 615-628.
Finch, N. C. et al. (2022). Evaluation of ionized calcium and parathyroid hormone concentrations in cats with postoperative hypocalcemia. Journal of Veterinary Internal Medicine, 36(4), 1312-1321.

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