What lab tests are used to diagnose zinc deficiency in high-risk patients, such as pregnant women, young children, and individuals with gastrointestinal diseases or malabsorption syndromes?

Lab Tests for Zinc Deficiency

Plasma or serum zinc is the primary and most widely used test to diagnose zinc deficiency, but it must always be interpreted alongside simultaneous CRP and albumin measurements to account for inflammation and protein status. 1

Primary Diagnostic Test

Plasma/Serum Zinc Measurement

• Plasma zinc remains the gold standard for confirming clinical zinc deficiency and monitoring adequacy of zinc provision in high-risk patients including pregnant women, young children, and those with gastrointestinal diseases. 1

• The preferred analytical methods are ICP-MS (inductively coupled plasma mass spectrometry) or atomic absorption spectroscopy. 1

• The lower end of the normal range in healthy adults is 60 mcg/dL (approximately 9.2 μmol/L). 2

Critical Interpretation Requirements

Mandatory Concurrent Testing

You cannot interpret zinc levels in isolation. Always order these simultaneously: 1

• CRP (C-reactive protein): Plasma zinc decreases significantly whenever CRP exceeds 20 mg/L due to acute phase response and zinc redistribution from plasma to liver. 1

• Albumin: Essential for interpretation since zinc binds to albumin in plasma. 1

Common Pitfall: Inflammation causes rapid zinc redistribution from plasma albumin to hepatic metallothionein, falsely lowering measured zinc levels even when total body zinc is adequate. This occurs within hours perioperatively and in acute illness. 1

Timing and Collection Considerations

Sample Collection Requirements

• Avoid hemolyzed samples: Hemolysis falsely elevates zinc levels due to release from erythrocytes. 3, 2

• Timing matters: Serum zinc fluctuates by up to 20% during a 24-hour period, largely due to food ingestion. 1

• Follow laboratory-specific requirements for collection, processing, and storage to ensure accurate results. 2

Alternative Tests (Limited Clinical Utility)

Blood Cell Zinc

• Neutrophil, lymphocyte, and platelet zinc content declines more rapidly than plasma zinc in experimental depletion studies. 1

• However, technical difficulties make this impractical for routine hospital use. 1

• Notably, erythrocyte zinc shows little or no change even when plasma zinc falls significantly during induced deficiency. 1

Hair Zinc

• Some evidence exists for low hair zinc in children with poor growth. 1

• Not recommended for hospital practice due to difficulties in collection (multiple contaminants) and interpretation challenges. 1

Monitoring Frequency for High-Risk Populations

Patients on Parenteral Nutrition

• Measure zinc at initiation if receiving PN for more than two weeks, especially with increased gastrointestinal or skin losses. 1

• Repeat every 6-12 months for long-term PN patients. 1

Post-Bariatric Surgery Patients

• Check serum/plasma zinc at 3,6, and 12 months in the first year following sleeve gastrectomy, Roux-en-Y gastric bypass, or biliopancreatic diversion/duodenal switch. 1

• Monitor at least annually thereafter. 1

• Check immediately if unexplained anemia, hair loss, or changes in taste acuity develop. 1

Pregnant Women and Children

• High-risk groups include vegetarians, alcoholics, teenagers, women with multiple pregnancies, and those with impaired intestinal absorption. 4

• Monitor based on clinical suspicion and presence of risk factors such as growth delays, recurrent infections, or characteristic skin changes. 5

When to Test Urgently

Check zinc levels immediately if: 1, 6, 7

• Unexplained anemia (especially with copper deficiency features)
• Hair loss or alopecia
• Changes in taste acuity or poor appetite
• Poor wound healing
• Characteristic skin rash (face, groins, hands, feet)
• Growth retardation in children
• Recurrent infections or immune dysfunction
• Chronic diarrhea or steatorrhea in malabsorption syndromes

Adjustment for Inflammation

• The BRINDA (Biomarkers Reflecting Inflammation and Nutritional Determinants of Anemia) group developed an R package with inflammation adjustment equations for serum zinc using CRP or AGP (alpha-1-acid glycoprotein) for various population groups. 1

• While no universal adjustment tool exists, this represents the best available method for correcting zinc values in the presence of inflammation. 1