In a patient with hypo- or hypercalcemia, what other lab must be ordered and why?

In a patient with hypo- or hypercalcemia, what other lab must be ordered and why?

• A. Albumin because 50% of calcium is protein bound
• B. Parathyroid hormone
• C. Phosphate
• D. Magnesium

Answer: (A)

Calcium in the blood is partly bound to proteins (mostly albumin) and partly free as ionized calcium. About half of calcium is bound to albumin, so the total calcium level depends on the albumin level. If albumin is low, total calcium can look low even though the active ionized calcium is normal; if albumin is high, total calcium can appear high. To interpret a calcium abnormality, you must check albumin to correct the total calcium (or measure ionized calcium directly). A common correction is to adjust total calcium based on albumin, or obtain ionized calcium for precise status. Other labs like PTH, phosphate, or magnesium are important for etiologic workup, but albumin directly affects how we interpret the calcium value.

Calcium in the blood is partly bound to proteins (mostly albumin) and partly free as ionized calcium. About half of calcium is bound to albumin, so the total calcium level depends on the albumin level. If albumin is low, total calcium can look low even though the active ionized calcium is normal; if albumin is high, total calcium can appear high. To interpret a calcium abnormality, you must check albumin to correct the total calcium (or measure ionized calcium directly). A common correction is to adjust total calcium based on albumin, or obtain ionized calcium for precise status. Other labs like PTH, phosphate, or magnesium are important for etiologic workup, but albumin directly affects how we interpret the calcium value.