The serum calcium test measures the amount of calcium in the blood. Calcium is an essential mineral that plays a key role in bone health, muscle function, nerve transmission, and blood clotting. There are two types of calcium that can be measured:

• Total calcium: Measures both bound and unbound (free) calcium.
• Ionized (free) calcium: Measures only the unbound calcium, which is the biologically active form.

Risk Assessment

The test is commonly ordered to assess:

• Parathyroid function
• Kidney function
• Bone disorders (like osteoporosis or osteomalacia)
• Certain cancers (e.g., hypercalcemia in cancer patients)
• Symptoms of calcium imbalance, such as muscle cramps, fatigue, or confusion.

People at risk for calcium imbalances include:

• Individuals with kidney disease
• People with hormonal disorders (e.g., hyperparathyroidism)
• Those taking medications that affect calcium levels (e.g., diuretics).

Normal Range

• Total calcium: 8.5 to 10.2 mg/dL (depending on the lab and methods used)
• Ionized calcium: 4.6 to 5.3 mg/dL

(Note: Reference ranges can vary slightly depending on the lab and population.).

Interpretation

• High calcium levels (Hypercalcemia) can indicate:
  • Hyperparathyroidism
  • Cancer
  • Kidney disease
  • Vitamin D overdose
• Low calcium levels (Hypocalcemia) can indicate:
  • Hypoparathyroidism
  • Vitamin D deficiency
  • Chronic kidney disease
  • Magnesium deficiency.

Sample Type

• Blood sample: A blood draw from a vein (venipuncture) is required.
  • For ionized calcium, the blood must be collected in a specific way to avoid contamination by air.