Calcium
Overview
Calcium measures the primary divalent cation essential for bone mineralization, muscle contraction, nerve transmission, and blood coagulation. It circulates bound to albumin, complexed with anions, or as ionized free calcium, with total calcium reflecting overall status while ionized provides physiological activity. Elevated levels (hypercalcemia) may indicate hyperparathyroidism, malignancy, or vitamin D excess, while low levels (hypocalcemia) suggest hypoparathyroidism, vitamin D deficiency, or renal failure. It is clinically useful for evaluating bone metabolism disorders, parathyroid function, and electrolyte imbalances.[pmc.ncbi.nlm.nih]Clinical Use Cases
- Diagnosing hyperparathyroidism or hypoparathyroidism.
- Evaluating chronic kidney disease-mineral bone disorder.
- Monitoring malignancy-associated hypercalcemia.
- Assessing osteoporosis risk and treatment response.
Specimen Types
- Serum (preferred for total calcium).
- Plasma (heparin for ionized calcium).
- Whole blood (point-of-care ionized).
Measurement Methods
- Colorimetric assay (o-cresolphthalein complexone).
- Ion-selective electrode (for ionized calcium).
- Atomic absorption spectrometry.
Test Preparation and Influencing Factors
- Fasting preferred; avoid tourniquet use.
- Albumin levels affect total calcium (correct via formula).
- Acidosis increases ionized; alkalosis decreases it.
- Lipemia, hemolysis, or hyperbilirubinemia interfere.
Synonyms
- Serum calcium.
- Total calcium.
- Ionized calcium (iCa).
Further Reading
- Calcium Blood Test; MedlinePlus;