Felis ISSN 2398-2950


Contributor(s): Jana Gordon, Chiara Valtolina


  • Definition:
    • Low total serum calcium concentration< 7mg/dl.
    • Low ionized serum calcium concentration < 1.1 mmol/L.
  • Calcium is important for many intra and extracellular functions. Required for bone formation, muscle contraction, nerve conduction, neuromuscular transmission, enzymatic reactions, blood coagulation, maintenance of vascular tone, regulation of hormones (PTH, calcitonin, vitamin D), cell growth and division.
  • Total calcium is composed of 50% ionized calcium (iCa), 40% protein bound calcium (pCa) and 10% complexed calcium. iCa is the biologically active fraction.
  • Calcium regulation is a complex process involving parathyroid hormone ( PTH), vitamin D metabolites and calcitonin.
  • Clinical signs are usually present when serum tCa is less than 6 mg/dL or iCa is less than 0.8 mmol/L.



  • Most of the clinical signs are associated with increased neuromuscular tissue excitability.
  • Different causes for hypocalcemia:
  • Common cause:
    • Low concentrations of binding proteins:
      • Hypoalbuminemia Hypoproteinemia. (Usually not clinical relevant as affect the protein bound fraction and ionized calcium unaffected. Correction formulas only appropriate for animals with low total protein or albumin and no longer commonly used. Should be confirmed with ionized calcium.)
    • Chronic renal failure Kidney: chronic kidney disease:
      • Decrease calcitriol synthesis (reduced calcium intestinal absorption and increased skeletal resistance to PTH) and increase phosphorus serum concentration.
    • Puerperal tetany:
      • Loss of calcium into the milk during lactation, fetal skeletal ossification, and parathyroid dysfunction.
    • Acute pancreatitis Pancreatitis:
      • Sequestration or saponification of calcium in the peri-pancreatic fat, increased calcitonin and hypomagnesemia Hypomagnesemia. Possible glucagon-stimulated release of calcitonin as well as decrease in PTH and hypomagnesemia.
    • Acute renal failure Kidney: acute renal failure.
  • Occasional cause:
    • Hypoparathyroidism Hypoparathyroidism (decreased or absent PTH secretion)
      • Primary:
        • Idiopathic or spontaneous.
        • Post-operative bilateral thyroidectomy.
      • After sudden reversal of chronic hypercalcemia Hypercalcemia: overview (as result of parathyroid gland atrophy).
      • Secondary to magnesium depletion or excess (inhibition of PTH).
    • Ethylene glycol intoxication Ethylene glycol poisoning (chelation of iCa with oxalic acid).
    • Phosphate enema.
    • After sodium bicarbonate administration Sodium bicarbonate.
  • Uncommon cause:
    • Laboratory error.
    • Improper sample anticoagulant handling (contamination with EDTA).
    • Rapid intravenous infusion of phosphate.
    • Rapid infusion of calcium-free fluid (rare).
    • Intestinal malabsorption.
    • Severe starvation.
    • Hypovitaminosis D (secondary to malabsorption).
    • Nutritional secondary hyperparathyroidism Nutritional secondary hyperparathyroidism.
    • Tumor lysis syndrome (from rapid increase in phosphate and deposition of calcium /phosphate complexes).
    • Blood transfusion (citrate anticoagulant) Blood transfusion.


  • None.


  • None.


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Further Reading


Refereed papers

Other sources of information

  • Small Animals Critical Care Medicine (2008) Eds D C Silverstein and K Hopper. Saunders Elsevier, S Louis Missouri.
  • Fluid, Electrolytes and acid-base Disorders in Small Animal Practice (2006) Eds S P DiBartola, Saunders Elsevier , St Louis Missouri.
  • The Veterinary ICU Book (2002) Eds W E Wingfield and M R Raffee. Teton New Media, Jackson Hole, WY.