Hypocalcemia is defined as a blood ionized calcium (iCa) level < 6.5 mg/dL (< 1.25 mmol/L) (normal 9 - 11.4 mg/dL).
Serum total calcium does not accurately predict ionized calcium status in many clinical conditions. Calcium homeostasis in hypoalbuminemic critically ill dogs should be evaluated by iCa concentrations rather than total calcium or calcium adjusted for albumin or total protein.
Calcium is a vital intracellular and extracellular ion involved in neuronal activation, muscle contraction, enzymatic reactions, hormone secretion, and bone matrix.
Normal calcium homeostatic mechanisms maintain extracellular calcium concentrations within a narrow normal range and changes often result in abnormal skeletal and cardiac muscle activity.
Extracellular calcium exists in three forms: ionized (the biologically active form), complexed (to plasma buffers), and protein-bound (mainly to albumin). Most commonly, total calcium is measured on serum biochemical analyses and represents the sum of all calcium fractions. Serum-ionized calcium (iCa) concentration is a more accurate measure of hypercalcemia than total serum calcium or corrected serum calcium concentrations.
In dogs with hypocalcemia, the low concentration of calcium causes an excitatory effect on nerve and muscle cells, lowering the threshold potential and discharging repetitively without provocation. Tetany occurs as a result of spontaneous repetitive firing of motor nerve fibers.
Hypoglycemia can occur concurrently in dogs.
Although commonly observed in young dogs associated with inadequate dietary calcium, a number of disease may also cause hypocalcemia, including:
- congenital rickets
- chronic renal disease
- metabolic alkalosis
- primary hypoparathyroidism
- diabetic ketoacidosis
- nutritional secondary hyperparathyroidism (rickets) 
- milk fever (eclampsia; puerperal hypocalcemia)
- following parathyroidectomy in dogs with primary hyperparathyroidism
- phosphate-containing enemas
- inflammatory bowel disease
- oxalate toxicity (e.g., lily, philodendron, etc.)
In dogs with nutritional secondary hyperparathyroidism, clinically affected dogs often present with joint pain due to osteopenia, which can be confirmed on radiographs.
Treatment involves addressing the acute hypocalcemia with parenteral calcium gluconate (10 mL of 10% calcium gluconate in 250 mL of 0.9% saline administered at 2.5 mL/kg/hr for 8 – 12 hours).
Severe and persistent hypocalcemia is associated with ventricular tachyarrhythmias and fibrillation, leading to sudden death.
- ↑ Schenck PA & Chew DJ (2008) Calcium: total or ionized? Vet Clin North Am Small Anim Pract 38(3):497-502
- ↑ Sharp CR et al (2009) A comparison of total calcium, corrected calcium, and ionized calcium concentrations as indicators of calcium homeostasis among hypoalbuminemic dogs requiring intensive care. J Vet Emerg Crit Care (San Antonio) 19(6):571-578
- ↑ Messinger JS et al (2009) Ionized hypercalcemia in dogs: a retrospective study of 109 cases (1998-2003). J Vet Intern Med 23(3):514-519
- ↑ LeVine DN et al (2009) Hereditary 1,25-dihydroxyvitamin D-resistant rickets in a Pomeranian dog caused by a novel mutation in the vitamin D receptor gene. J Vet Intern Med 23(6):1278-1283
- ↑ Hume DZ et al (2006) Outcome of dogs with diabetic ketoacidosis: 127 dogs (1993-2003). J Vet Intern Med 20(3):547-555
- ↑ Krook L & Whalen JP (2011) Nutritional secondary hyperparathyroidism in the animal kingdom: report of two cases. Clin Imaging 34(6):458-461
- ↑ Drobatz KJ & Casey KK (2000) Eclampsia in dogs: 31 cases (1995-1998). J Am Vet Med Assoc 217(2):216-219
- ↑ Kimmel SE et al (2000) Hypomagnesemia and hypocalcemia associated with protein-losing enteropathy in Yorkshire terriers: five cases (1992-1998). J Am Vet Med Assoc 217(5):703-706
- ↑ Arbaugh M et al (2012) Evaluation of preoperative serum concentrations of ionized calcium and parathyroid hormone as predictors of hypocalcemia following parathyroidectomy in dogs with primary hyperparathyroidism: 17 cases (2001-2009). J Am Vet Med Assoc 241(2):233-236
- ↑ Holowaychuk MK & Monteith G (2011) Ionized hypocalcemia as a prognostic indicator in dogs following trauma. J Vet Emerg Crit Care (San Antonio) 21(5):521-530
- ↑ Tomsa K et al (2001) Life threatening metabolic disorders after application of a sodium phosphate containing enema in the dog and cat. Schweiz Arch Tierheilkd 143(5):257-261
- ↑ Kook PH et al (2009) Pancreatitis associated with clomipramine administration in a dog. J Small Anim Pract 50(2):95-98
- ↑ Gow AG et al (2011) Hypovitaminosis D in dogs with inflammatory bowel disease and hypoalbuminaemia. J Small Anim Pract 52(8):411-418
- ↑ Luschini MA et al (2010) Incidence of ionized hypocalcemia in septic dogs and its association with morbidity and mortality: 58 cases (2006-2007). J Vet Emerg Crit Care (San Antonio) 20(4):406-412
- ↑ Brauer C et al (2011) Metabolic and toxic causes of canine seizure disorders: A retrospective study of 96 cases. Vet J 187(2):272-275
- ↑ Hutchinson D et al (2012) Seizures and severe nutrient deficiencies in a puppy fed a homemade diet. J Am Vet Med Assoc 241(4):477-483
- ↑ Ricco ML et al (2009) Effects of hypocalcemia on electrical restitution and ventricular fibrillation. Conf Proc IEEE Eng Med Biol Soc 2009:4182-4185