Can serum zinc be used to diagnose zinc deficiency? Why?

• A. Yes, serum zinc is a reliable indicator
• B. No, serum zinc is not reliable; may be normal; low in SIRS; caution with hypoalbuminemia
• C. Yes, but only if urinary zinc is also low
• D. It is always normal in deficiency

Answer: (B)

Serum zinc concentration is not a reliable stand-alone test for diagnosing zinc deficiency because zinc in the blood reflects rapid shifts in distribution rather than total body stores. Inflammation and the acute phase response can pull zinc out of the serum and into the liver and other tissues, so serum levels may be low during illness even if stores are adequate. Conversely, many people with true deficiency can have normal serum zinc. Albumin, the main carrier of zinc in plasma, also influences serum levels, so hypoalbuminemia can lead to misleadingly low readings. Because of these factors, a normal serum zinc does not exclude deficiency, and a low reading can be driven by inflammation or low albumin rather than true deficiency. Therefore, diagnosis should rely on clinical assessment, dietary data, growth or functional indicators, and consideration of inflammatory status, rather than serum zinc alone.