As albumin decreases, what happens to serum calcium level?

• A. Increases
• B. Remains unchanged
• C. Decreases
• D. Becomes unpredictable

Answer: (C)

Calcium in the blood exists in two forms: a physiologically active free (ionized) portion and a larger portion bound to proteins, mainly albumin. When albumin levels drop, less calcium is available to be bound, so the total amount of calcium measured in serum falls. However, the amount of ionized calcium—the part that actually does the work in the body—remains largely unchanged unless there are other disturbances. So the observed total serum calcium decreases as albumin decreases, while the clinically important ionized calcium stays relatively stable. In practice, clinicians often correct the total calcium for low albumin or measure ionized calcium to avoid misinterpretation.