What lab tests are used to monitor zinc deficiencies?

From the Guidelines

Plasma zinc levels are the primary lab test used to monitor zinc deficiencies. This determination remains the most widely used test to confirm clinical zinc deficiency and to monitor adequacy of provision 1. The normal values for plasma zinc levels typically range from 70-120 μg/dL, but these measurements can be unreliable as zinc is predominantly stored intracellularly, making serum levels less reflective of total body zinc status.

Key Points to Consider

• Alternative tests include plasma zinc concentration, urinary zinc excretion, and erythrocyte zinc levels.
• Clinicians may also measure alkaline phosphatase activity, which is a zinc-dependent enzyme that decreases with deficiency.
• In some cases, hair or nail zinc analysis may provide information about longer-term zinc status.
• For more comprehensive assessment, functional tests like taste acuity (dysgeusia is common in zinc deficiency) or immune function tests may be used.
• It's essential to note that inflammation can artificially lower serum zinc levels, so C-reactive protein should be measured simultaneously to rule out this confounding factor, as suggested by the espen micronutrient guideline 1.

Patient Groups Requiring Special Consideration

• Zinc deficiency testing is particularly important for patients with malabsorption disorders, alcoholism, vegetarian diets, or those taking medications that deplete zinc.
• Patients undergoing bariatric surgery, such as sleeve gastrectomy (SG), Roux-en-Y gastric bypass (RYGB), or biliopancreatic diversion with duodenal switch (BPD/DS), may require regular monitoring of serum/plasma zinc levels, as recommended by the British Obesity and Metabolic Surgery Society guidelines 1.

Monitoring and Replacement

• The complete multivitamin and mineral supplement may not contain sufficient zinc to prevent deficiency following SG, RYGB, or BPD/DS, and additional zinc supplements may be necessary, with a recommended starting dose of 15 mg/d zinc, which may be contained within the multivitamin and mineral supplement 1.
• A ratio of 8-15 mg of zinc for each 1-mg copper should be maintained to avoid zinc-induced copper deficiency, and both zinc and copper levels should be monitored when considering zinc or copper replacement 1.

From the FDA Drug Label

Monitor zinc concentrations and signs and symptoms of zinc deficiency, especially in pediatric patients, during treatment. Zinc concentrations may vary depending on the assay used and the laboratory reference range. The collection, processing, and storage of the blood samples for zinc analysis should be performed according to the laboratory's sample requirements. Zinc concentrations in hemolyzed samples are falsely elevated due to release of zinc from erythrocytes The lower end of the reported range in healthy adults in serum is 60 mcg/dL.

The lab test used to monitor zinc deficiencies is serum zinc concentration.

• Key points to consider when monitoring zinc concentrations:
  • Use an appropriate assay
  • Follow the laboratory's sample requirements for collection, processing, and storage of blood samples
  • Be aware that hemolyzed samples can give falsely elevated results
  • Compare results to the laboratory's reference range, with the lower end of the reported range in healthy adults being 60 mcg/dL 2

From the Research

Lab Tests for Zinc Deficiencies

The following lab tests are used to monitor zinc deficiencies:

• Serum zinc concentration: This is a common test used to assess zinc status, with cutoffs varying by age and sex 3, 4, 5
• Urinary zinc excretion: This test can be used to assess zinc absorption, particularly with doses of 50-100 mg of elemental zinc 6
• Zinc tolerance test: This test involves measuring plasma zinc concentrations after oral zinc administration to assess zinc absorption 6, 5
• Measurement of activities of zinc-dependent enzymes: This can include assays such as alkaline phosphatase in neutrophils 5
• Metabolic balance studies: These studies can help assess zinc status by measuring zinc intake and excretion 5
• Cu:Zn ratio: This ratio can be used to assess zinc status and potential copper deficiency 4, 5
• Hair zinc levels: While not as sensitive to recent changes in zinc status, hair zinc levels can provide information on long-term zinc status 5
• Erythrocyte zinc levels: Like hair zinc levels, erythrocyte zinc levels can provide information on long-term zinc status, but may not reflect recent changes 5