What is the normal calcium range in mg/dL?

• A. 8.5-10.5 mg/dL
• B. 7.0-9.0 mg/dL
• C. 9.0-11.0 mg/dL
• D. 10.0-12.0 mg/dL

Answer: (A)

Calcium in the blood is normally around 8.5 to 10.5 mg/dL. Think of calcium existing in two main forms in the blood: ionized (free) calcium, which is the physiologically active part, and calcium that is bound to proteins like albumin. The value most often reported as total calcium combines both forms, so it can be influenced by a person’s albumin level. Ionized calcium, the active portion, is typically about 1.1 to 1.3 mmol/L (roughly 4.5 to 5.5 mg/dL). This is why the standard reference for total calcium is 8.5–10.5 mg/dL: it reflects the usual amount present when albumin isn’t abnormal. If albumin is low, total calcium can appear low even though ionized calcium is normal, so clinical interpretation should consider albumin and, when needed, measure ionized calcium directly.