In tetany due to hypocalcemia, the calcium level is typically which of the following?

• A. Low
• B. High
• C. Normal
• D. Variable depending on magnesium status

Answer: (A)

Calcium stabilizes nerve and muscle membranes. When extracellular calcium is low, membranes become more excitable, lowering the threshold for action potentials and producing spontaneous, painful contractions—tetany. In tetany due to true hypocalcemia, the circulating calcium, especially the physiologically active ionized calcium, is reduced. Albumin can affect total calcium readings, so a normal total calcium doesn’t exclude low ionized calcium, and magnesium status can influence calcium homeostasis, but the typical scenario that produces tetany is a low calcium level. Hence, the calcium level is low.