DEFINITION
Total serum calcium has 3 components:
- A protein-bound component - About 45% is protein bound (predominantly bound to albumin); this component is biologically inert
- A component that is complexed or chelated to citrate - About 5%; this component is also biologically inert
- An ionized or free component - About 50%; this component is metabolically active
Total calcium Reference Range
- Normal values range from 8.5 to 10.2 mg/dL.
Medscape Reference Range
Ionized calcium represents the true bioavailable calcium in the circulation. In situations where the total calcium is normal, but does not fit the clinical picture, a determination of the ionized calcium has to be performed.
Ionized calcium Reference Range
- Children: 4.4 - 6.0 milligrams per deciliter (mg/dL)
- Adults: 4.4 - 5.3 mg/dL
Comparative studies of total and ionized serum calcium values in normal subjects and patients with renal disorders. 1980
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ANALYTICAL METHOD
In most laboratories, autoanalyzers are used measure the total serum calcium level accurately and reproducibly, although atomic absorption spectrophotometers probably provide even greater accuracy.
ANALYTICAL TRICKS AND TIPS
THE BIOLOGICAL CONTEXT
Serum calcium is involved in the regulation of neuromuscular and enzyme activity, bone metabolism, and blood coagulation. Calcium blood levels are controlled by a complex interaction of parathyroid hormone, Vitamin D, calcitonin, and adrenal cortical steroids. Calcium measurements are useful in the diagnosis of parathyroid disease, some bone disorders, and chronic renal disease. A low level of calcium results in tetany.
DIAGNOSTIC USE
Issues
Specificity, sensitivity etc.
Diagnostic Algorithms
PROs and CONTROs
Open Questions
Working Hypothesis
