What is the best course of action for a patient with a mildly elevated TSH (Thyroid-Stimulating Hormone) level, normal FT3 (Free Triiodothyronine) level, slightly elevated FT4 (Free Thyroxine) level, and symptoms of palpitations?

Immediate Evaluation for Thyroid Hormone Resistance or Assay Interference

Your laboratory results showing normal TSH (2.63) with markedly elevated FT4 (27.73) and high-normal FT3 (6.59) are biochemically discordant and require urgent investigation for either thyroid hormone resistance syndrome or laboratory assay interference before any treatment decisions are made. 1

Critical First Steps: Rule Out Laboratory Error

• Repeat thyroid function tests on a different analyzer platform immediately - your pattern of normal TSH with elevated FT4/FT3 is classic for assay interference, which occurs when antibodies or other substances falsely elevate measured thyroid hormone levels 2
• Request testing on both Abbott and Roche platforms if possible, as interference patterns differ between manufacturers 2
• The discordance between your TSH (which suggests euthyroidism) and FT4 (which suggests hyperthyroidism) makes assay interference the most likely explanation 2

If Assay Interference is Confirmed

• No treatment is needed - your actual thyroid status is likely euthyroid based on the normal TSH 2
• The palpitations are unrelated to thyroid dysfunction and require separate cardiovascular evaluation 2
• Annual TSH monitoring is sufficient going forward 3

If Thyroid Hormone Resistance is Confirmed

Diagnostic Criteria

• Thyroid hormone resistance presents with elevated FT4 and FT3 alongside inappropriately normal or slightly elevated TSH - your TSH of 2.63 fits this pattern 1
• The characteristic clinical feature is absence of hyperthyroid symptoms despite elevated thyroid hormones 1
• Family history of similar thyroid test patterns strongly supports this diagnosis 1

Management Approach

• Most patients with thyroid hormone resistance require no treatment as they are clinically euthyroid despite elevated hormone levels 1
• Your palpitations warrant cardiac evaluation (ECG, Holter monitor) but are unlikely related to thyroid hormone resistance 1
• Genetic testing for TRβ gene mutations can confirm the diagnosis and guide family counseling 1

Addressing Your Palpitations

• Do not attribute palpitations to thyroid dysfunction based on these results - the normal TSH indicates your tissues are not experiencing thyroid hormone excess 3, 1
• Obtain ECG to screen for arrhythmias, particularly atrial fibrillation 3
• Consider 24-hour Holter monitoring if palpitations are frequent 3
• Evaluate for other causes: caffeine intake, anxiety, anemia, electrolyte abnormalities 3

Critical Pitfalls to Avoid

• Never initiate antithyroid medication based on elevated FT4 alone when TSH is normal - this pattern demands investigation, not treatment 1, 2
• Do not assume hyperthyroidism is causing symptoms when TSH is in the normal range 1
• Avoid repeating tests on the same analyzer platform - interference will persist 2
• Do not order thyroid imaging or radioactive iodine uptake scans until assay interference is excluded 1

Expected Timeline

• Repeat testing on alternate platform: within 1 week 2
• If assay interference confirmed: no further thyroid workup needed 2
• If thyroid hormone resistance suspected: referral to endocrinology for genetic testing and family screening 1
• Cardiac evaluation for palpitations: proceed immediately regardless of thyroid results 3