Serum zinc (plasma zinc) measures circulating zinc concentration, providing a widely available assessment of zinc status. Zinc is an essential trace mineral required as a structural cofactor for over 300 enzymes and 2,000 transcription factors involved in immune function, protein synthesis, wound healing, DNA synthesis, taste and smell, growth, and antioxidant defence.

Serum zinc has significant limitations: it represents only 0.1% of total body zinc, is tightly regulated within a narrow range, is acutely suppressed by inflammation (falsely appearing low), and falls with low albumin. Despite these limitations, it remains the most widely available zinc status marker. Testing should be performed as a morning fasting specimen for most accurate results.