Testing for Zinc Deficiency in Nutritional Assessment
Plasma zinc testing is recommended for assessing zinc status in patients with clinical suspicion of deficiency, but routine screening is not indicated for most patients due to limitations in interpretation and clinical utility. 1
When to Test for Zinc Deficiency
Zinc testing should be performed selectively based on risk factors and clinical presentation:
High-Risk Populations
- Patients with gastrointestinal losses (fistulae, stomas, diarrhea) 1
- Patients on long-term parenteral nutrition 1
- Post-bariatric surgery patients (particularly SG, RYGB, or BPD/DS) 1
- Patients with malabsorption syndromes 1, 2
- Patients with liver or renal disease 2
- Patients taking high-dose zinc supplements (risk of induced copper deficiency) 3
Clinical Indications
- Unexplained hair loss 1
- Changes in taste acuity 1, 2
- Unexplained anemia 1
- Poor wound healing 2
- Dermatitis or skin lesions 2
- Recurrent infections 4
- Growth retardation (in children) 4
Testing Methodology and Interpretation
Recommended Test
- Plasma/serum zinc is the most widely used and accessible test 1
- Must be collected in trace element-free tubes to avoid contamination
- Fasting samples are preferred (levels fluctuate by up to 20% during a 24-hour period) 1
Critical Considerations for Interpretation
- Always measure CRP and albumin simultaneously with zinc levels 1
- Inflammation significantly decreases plasma zinc (redistribution to liver)
- Plasma zinc decreases whenever CRP exceeds 20 mg/L 1
- Hypoalbuminemia affects zinc levels (zinc binds to albumin)
- Avoid hemolyzed samples (falsely elevated due to release from erythrocytes) 5
- Collection timing matters (diurnal variation and postprandial effects)
Monitoring Recommendations
For high-risk patients requiring monitoring:
- Post-bariatric surgery: Check zinc levels at least annually 1
- Long-term parenteral nutrition: Check every 6-12 months 1
- When supplementing zinc: Monitor both zinc and copper levels (zinc supplementation can induce copper deficiency) 1, 3
Limitations of Zinc Testing
- Plasma zinc represents only 0.1% of total body zinc 6
- Levels are affected by numerous factors unrelated to nutritional status:
- Acute stress
- Infections
- Myocardial infarction
- Intravascular hemolysis 6
- Normal plasma levels don't exclude tissue deficiency
Alternative Assessment Methods
When zinc deficiency is strongly suspected despite normal plasma levels:
- Clinical response to therapeutic trial of zinc supplementation may be diagnostic 2
- In research settings, neutrophil zinc and alkaline phosphatase activity in neutrophils may be more sensitive indicators 6
Treatment Approach
If deficiency is confirmed:
- For acquired zinc deficiency: 0.5-1 mg/kg/day of elemental zinc for 3-4 months 1
- Organic compounds (zinc histidinate, gluconate, orotate) have better tolerability than inorganic forms 1
- Monitor copper levels during zinc supplementation (zinc induces metallothionein which binds copper) 3
Zinc deficiency has significant clinical implications including impaired immune function, poor wound healing, and increased susceptibility to infections 4, 7. However, testing should be targeted to those with risk factors or clinical manifestations rather than used as a routine screening tool.