Do individuals with thyroid antibodies need to be tested for selenium deficiency?

Testing for Selenium Deficiency in Patients with Thyroid Antibodies

Routine selenium testing is not necessary for all patients with thyroid antibodies, but plasma selenium measurement should be obtained if you are considering supplementation or if the patient has clinical features suggesting deficiency. 1, 2

When to Test

Measure plasma selenium levels in antibody-positive patients when:

• You are considering selenium supplementation for autoimmune thyroiditis or Graves' disease 2
• The patient has risk factors for deficiency including: long-term enteral nutrition, malabsorption disorders, burns, major trauma, or continuous renal replacement therapy 1
• The patient lives in a geographic area known for selenium-poor soil 3
• You need to establish baseline values before initiating supplementation to guide dosing and monitor response 2

How to Interpret Results

Target plasma selenium concentration is ≥0.75 μmol/L (≥59 μg/L) in patients without inflammation. 1

• Values <0.4 μmol/L (<32 μg/L) always warrant supplementation 1
• Values between 0.4-0.75 μmol/L indicate relative deficiency and may benefit from supplementation, particularly in autoimmune thyroid disease 1, 2
• Inflammation significantly affects results: CRP 10-40 mg/L causes 15-25% reduction in plasma selenium; CRP 41-80 mg/L causes ~35% reduction; CRP >80 mg/L causes ~50% reduction 1

Always measure CRP simultaneously with selenium to interpret results correctly. 1

Additional Testing Considerations

For more comprehensive assessment, consider adding:

• Glutathione peroxidase-3 (GPX-3) to reflect functional selenium status and short-term changes 1, 2
• Red cell glutathione peroxidase (GPX-1) for longer-term selenium status assessment over the erythrocyte lifespan 1

Clinical Context for Thyroid Antibody-Positive Patients

The decision to test should be driven by whether you plan to supplement, not by antibody presence alone. 2

• Selenium supplementation in Hashimoto's thyroiditis reduces anti-TPO antibody levels by approximately 36-40% in patients with high antibody titers (>1200 IU/mL) 4
• For mild thyroid eye disease in Graves' disease, selenium supplementation (100 μg/day) reduces inflammatory symptoms and delays progression 2, 3
• Selenium supplementation does not impact hyperthyroidism control in selenium-replete populations 2

Important Caveats

Do not test or supplement indiscriminately:

• Testing is costly when done routinely without clinical indication—one study showed $13 per patient just for laboratory draws, plus additional staff time 1
• Upper toxicity threshold is 6-12 μmol/L, with selenosis causing headache, hair/nail loss, skin rash, and neurological symptoms 2
• High-dose supplementation (1000-4000 μg/day) shows no consistent benefit and is not recommended 2
• Long-term supplementation may increase diabetes risk 5

Test selectively based on clinical context, planned intervention, and risk factors rather than reflexively in all antibody-positive patients. 1, 2