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Blood biochemistry: ionized calcium
Overview
- Calcium is present in blood in three compartments:
- Plasma protein bound.
- Complexed with small anions.
- Free ionized.
- Ionized form is biologically active.
- Ionized calcium comprises approximately 50% total calcium.
- Normal range for ionized calcium is very narrow.
- Total calcium Blood biochemistry: total calcium tends to reflect ionized calcium but this may not always be true in renal failure Kidney: chronic kidney disease (CKD) or animals with abnormal protein concentrations.
Uses
Alone
- To confirm that hyper- or hypocalcemia detected on assay of total calcium.
In combination
- With total calcium Blood biochemistry: total calcium and other parameters for assessment of chronic renal failure Kidney: chronic kidney disease (CKD).
- With total calcium Blood biochemistry: total calcium and parathyroid hormone assay PTH assay for assisting in differential diagnosis of hypercalcemia Hypercalcemia: overview and hypocalcemia Hypocalcemia.
- May help to distinguish patients with renal failure secondary to hypercalcemia from those with primary renal failure and terminal hypercalcemia Hypercalcemia: overview.
In primary renal failure ionized fraction is normal or low with high [PTH] and in primary hypercalcemia ionized fraction is high.
Sampling
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Tests
Methodologies
- Potassium chloride-saturated ion-specific electrode analysis.
Availability
- Available at some commercial laboratories and local hospitals (although reference values would need to be established for animals).
- In-house bench top analyzers can be purchased.
- Hand-held patient-side analyzers available.
Technique intrinsic limitations
- Simple technique.
Result Data
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Further Reading
Publications
Refereed papers
- Recent references from VetMedResource and PubMed.
- Schenck P A & Chew D J (2005) Prediction of serum ionized calcium concentration by use of serum total calcium concentration in dogs. Am J Vet Res 66 (8), 1330-1336 PubMed.
Other sources of information
- Ettinger S J & Feldman E C (2000) Eds. Textbook of Veterinary Internal Medicine. 5th edn. W B Saunders & Co, USA.
- Cowell R L, Tyler R D & Meinkoth J H (1999) Diagnostic Cytology and Hematology of the Dog and Cat. 2nd edn. Mosby, USA.
- Kaneko J J, Harvey J W & Brass M L (1997) Eds. Clinical Biochemistry of Domestic Animals. 5th edn. Academic Press, USA.
- Duncan J R, Prasse K W & Mahaffey E A (1994) Veterinary Laboratory Medicine. Clinical Pathology. 3rd edn. Iowa University Press, USA.