Serum zinc is the key indicator for assessing zinc deficiency among populations. Serum zinc reflects dietary zinc intake and responds consistently to zinc supplementation. Reference data are available for most age and sex groups. Assessing serum zinc allows the identification of specific populations and subgroups who have an elevated risk of zinc deficiency 1. Serum zinc cannot be used in the diagnosis and treatment of individuals who are zinc deficient because serum zinc concentrations are not a direct reflection of the individual’s zinc status 2. However, serum zinc can provide an assessment of the magnitude of the risk of zinc deficiency within a specific population or subgroup 1.

There are special considerations when measuring serum zinc concentration. Recent meals, the time of day, the age and sex of the participant, the use of hormonal contraception, inflammation and systemic infections all can have a direct impact on serum zinc concentration 2. The International Zinc Nutrition Consultative Group (IZiNCG) suggests collecting information on inflammatory proteins when assessing zinc, and if there is a significant negative correlation between either inflammatory protein and serum zinc, to adjust serum zinc concentration statistically 3.

Zinc concentrations in hair, nail and urine have been used in some studies to assess a population’s exposure to zinc; however, they are currently not recommended as a single indicator in the assessment of zinc status 4,5.

Specimen collection and management: There are special considerations when collecting serum specimens to assess zinc deficiency. Specimens can be easily contaminated by ambient sources of zinc during collection, processing and analysis. To reduce the risk of ambient zinc contamination, the blood specimen must be taken directly from the vein using zinc-free needles and trace-metal-free vacuum blood collection tubes. When processing the samples, zinc-free sterile storage vials and transfer pipettes or pipette tips must be used to reduce the risk of contamination. If possible, specimens should be collected from survey participants during a pre-agreed time of day, and the participants should have been fasting for at least eight hours prior to collection. Fasting conditions are not always possible, so if non-fasting specimens are collected, an effort must be made to reduce variation by collecting samples from the entire survey population during the same time of day. It is important to record the time of the previous meal, especially for calculating non-fasting cutoff values and interpreting data. Once a blood specimen has been collected, it should be stored in a cold box or a refrigerator until centrifuged to collect the serum.

Ideally, all specimens should be centrifuged within 20 to 30 minutes after collection. If this is not possible, it is recommended that processing be done within 24 hours, provided that the cold chain is reliable and blood specimens can be kept refrigerated (2–10°C). Specimens should also be centrifuged in a controlled laboratory environment and serum should be separated into vials under a laboratory hood. In situations where this is not feasible, it is recommended that a tent be used so that a sealed laboratory can be configured. Plastic boxes can be used along with plexiglass or plastic wrap to develop a temporary field hood. All necessary information specific to zinc-free laboratory supplies and the construction of a hood from a plastic box is available from IZiNCG.

Biomarker analysis: Zinc concentration can be measured using several different analytical methodologies. The gold standard is inductively coupled plasma mass spectrometry (ICP-MS), however, this method is very expensive. Other acceptable analytical methods to measure zinc concentration include inductively coupled plasma atomic emission spectrometry, flame atomic absorption spectrometry (AAS), graphite furnace atomic absorption spectrometry, and neuron activation analysis.

Approximate budget requirements for analysis: The cost for instrumentation can vary widely depending on use of AAS or ICP-MS, but is typically around US$ 50 000–US$ 400 000. The cost for materials and supplies is approximately US$ 10–20 per sample.

Interpretation of results: Data on low serum zinc concentration should be compared with the appropriate reference data for age, sex, time of day and time since last meal. Reference data have been derived from NHANES II and represent individuals older than 2 years of age. The IZiNCG-recommended cutoff values for low serum zinc concentration are presented in Table 3.10. It is important to note that if 20% of the population has low serum zinc concentration there is a risk for zinc deficiency and a public health concern 2.

Suggested lower cutoff values for low serum zinc concentration in µg/dL (µmol/L)b
Time of day and fasting status ≤10 years ≥10 years
Males and females Non-pregnant females Males
Morning, fastingc not available 70 (10.7) >74 (11.3)
Morning, non-fasting 65 (9.9) 66 (10.1) 70 (10.7)
Afternoon, non-fasting 57 (8.7) 59 (8.6) 61 (9.3)

a Source: reference 5.

b Values converted to µmol/L by dividing µg/dL by 6.54.

c Fasting is defined as no food or beverage consumption for at least 8 hours.

  1. Quantifying the risk of zinc deficiency: recommended indicators. Technical Brief No. 01. Davis: IZiNCG; 2007 (https://static1.squarespace.com/static/56424f6ce4b0552eb7fdc4e8/t/57493db901dbae66390e9dca/1464417728860/English_brief1.pdf; accessed 14 June 2020).  2

  2. Assessing population zinc status with serum zinc concentrations. IZiNCG Technical Brief No. 02. 2nd edition. Oakland: International Zinc Nutrition Consultative Group; 2012 (https://static1.squarespace.com/static/56424f6ce4b0552eb7fdc4e8/t/5774378f414fb5410541b748/1467234199261/IZiNCG_TechBrief2_2012-3.pdf, accessed 14 June 2020).  2 3

  3. Adjusting plasma or serum zinc concentrations for inflammation. IZiNCG Technical Brief No. 10. Oakland: International Zinc Nutrition Consultative Group; 2020 (https://static1.squarespace.com/static/56424f6ce4b0552eb7fdc4e8/t/5e9dff7f491e4343279045b8/1587412866032/IZiNCG_Technical+Brief+BRINDA_20Apr2020_final.pdf, accessed 14 June 2020). 

  4. King JC, Brown KH, Gibson RS, Krebs NF, Lowe NM, Siekmann JH et al. Biomarkers of Nutrition for Development (BOND) – zinc review. J Nutr. 2016;146:858S–885S. 

  5. Assessing population zinc exposure with hair or nail zinc. IZiNCG Technical Brief No. 8. Oakland: International Zinc Nutrition Consultative Group; 2008 (https://static1.squarespace.com/static/56424f6ce4b0552eb7fdc4e8/t/5b9af5cc2b6a28b42972103e/1536882147963/IZiNCg-TechnicalBrief-No.8-FINAL.pdf, accessed 14 July 2020).