B

Total (measured) serum calcium falls when albumin or other serum proteins are low, even though the physiologically important ionized calcium may be normal. Therefore, knowing the neonate’s serum protein/albumin allows you to interpret whether the calcium of 6 mg/dL truly reflects hypocalcemia or is simply “falsely” low due to hypoalbuminemia, and guides appropriate supplementation [Aggarwal 2001, PMID 11758136; Besarab 1981, PMID 7328184].