How do you test for selenium deficiency?

Testing for Selenium Deficiency

Blood selenium measurement is the primary method for assessing selenium status, with plasma/serum selenium being the most widely used clinical test, ideally accompanied by simultaneous CRP and albumin measurements to account for inflammatory effects. 1

Primary Testing Methods

Plasma/Serum Selenium

• Most commonly used clinical test for selenium status 1
• Requires interpretation with inflammatory markers (CRP) and albumin levels 1
• Reference values vary by geographical region due to soil selenium content 2
• Values <0.4 μmol/L (<32 μg/L) indicate definite deficiency requiring supplementation 1
• Values <0.75 μmol/L in patients without inflammation should trigger supplementation 1

Inflammatory Adjustment

• CRP must be measured simultaneously for proper interpretation 1
• Inflammation causes redistribution of selenium out of circulation 1
• Correction factors based on CRP levels:
  • CRP 10-40 mg/L: expect 15-25% reduction in plasma selenium
  • CRP 41-80 mg/L: expect ~35% reduction
  • CRP >80 mg/L: expect ~50% reduction 1

Additional Testing Options

Functional Tests

• Plasma glutathione peroxidase (GPX-3) measurement reflects functional selenium status 1
  • Correlates with plasma selenium but accounts for only ~20% of total plasma selenium
  • Useful for assessing short-term changes in selenium status
  • Grade A recommendation for combined testing with blood selenium 1

Alternative Sample Types

• Whole blood selenium provides a composite result (plasma + erythrocyte selenium) 1
• Red blood cell glutathione peroxidase (GPX-1) assesses longer-term selenium status 1
• Selenoprotein P measurement (accounts for >50% of plasma selenium) 1
• Urine selenium reflects recent dietary intake but is rarely used clinically 1
• Hair selenium analysis can indicate long-term intake but has limited clinical value due to contamination risks 1

Analytical Methods

• Inductively coupled plasma mass spectrometry (ICP-MS) is preferred for accuracy and sensitivity 3, 4
  • Lower detection limit (0.19 μg/L) compared to other methods 4
  • Better precision (5.9% vs 8% for AAS) 4
  • Allows multi-element analysis in a single run 4
• Atomic absorption spectroscopy (AAS) is an alternative but less sensitive method 4

Testing Recommendations

When to Test

• Test all patients likely to receive parenteral nutrition for >2 weeks 1
• Test patients starting home parenteral nutrition 1
• Consider testing in patients with symptoms of deficiency (muscle pain, tenderness) 2
• Consider testing in patients with Hashimoto's thyroiditis, as selenium supplementation may benefit those with deficiency 5

Follow-up Testing

• Repeat tests as required based on initial results 1
• For patients on parenteral nutrition, recheck at least every 3-6 months 1
• After supplementation for severe deficiency, recheck after 7-10 days of treatment 1

Clinical Pitfalls

• Failure to measure CRP with selenium leads to misinterpretation during inflammatory states 1
• Reference ranges vary geographically - use local reference ranges when available 1, 2
• Sample timing matters - serum selenium can fluctuate by 20% during a 24-hour period 1
• Prolonged enteral nutrition can lead to selenium deficiency depending on the product used 1
• Certain populations have higher requirements (burns patients, trauma patients, those on renal replacement therapy) 1

By following this structured approach to selenium testing, clinicians can accurately identify deficiency states and monitor response to supplementation.