A hospitalized patient is experiencing increased neuromuscular irritability (tetany). Which of the following tests should be ordered immediately?

• A. Calcium
• B. Phosphate
• C. BUN
• D. Glucose

Answer: (A)

Tetany reflects increased neuromuscular excitability from low calcium. Calcium normally stabilizes nerve membranes; when calcium is low, nerves become more excitable and muscles can contract involuntarily. In a hospitalized patient with this presentation, measuring serum calcium right away is essential because confirming hypocalcemia guides urgent treatment to restore calcium levels and relieve symptoms. Ionized calcium is especially informative in acute illness, since it reflects the physiologically active fraction and is less affected by albumin or pH than total calcium.

Phosphate, BUN, and glucose don’t directly explain or rapidly diagnose the tetany. Phosphate changes can occur in disorders affecting calcium, but it isn’t the immediate diagnostic target here, and BUN or glucose don’t account for the neuromuscular irritability seen with hypocalcemia.