What tests should be ordered for a patient with hyperthyroidism?

Diagnostic Tests for Hyperthyroidism

For patients with hyperthyroidism, a comprehensive laboratory evaluation should include thyroid function tests (TSH, free T4, free T3), thyroid autoantibodies (TSH receptor antibodies, thyroid peroxidase antibodies), complete blood count, comprehensive metabolic panel, and thyroid imaging studies. 1

Initial Laboratory Testing

Essential Tests

• Thyroid Function Tests

  • Thyroid-stimulating hormone (TSH) - typically suppressed
  • Free thyroxine (FT4) - typically elevated
  • Free triiodothyronine (FT3) - may be elevated, especially in Graves' disease 2, 3

• Thyroid Autoantibodies

  • TSH receptor antibodies (TRAb) - for diagnosis of Graves' disease
  • Thyroid peroxidase antibodies (TPOAb) - may help differentiate autoimmune causes 3, 4

• Basic Laboratory Panel

  • Complete blood count
  • Comprehensive metabolic panel (including liver function tests)
  • Serum electrolytes (including calcium and magnesium)
  • Blood glucose
  • Lipid profile 1

Imaging Studies

• Thyroid Ultrasound

  • Evaluates thyroid size, vascularity, and presence of nodules
  • Hypervascular and hypoechoic pattern typical in Graves' disease 4

• Radioactive Iodine Uptake (RAIU) and Scan

  • Differentiates between causes of hyperthyroidism:
    • Increased uptake: Graves' disease, toxic nodular goiter
    • Decreased uptake: thyroiditis, exogenous thyroid hormone 5, 3
  • Particularly useful when etiology is unclear or when nodules are present

Additional Testing Based on Clinical Presentation

• Cardiac Assessment

  • Electrocardiogram - to evaluate for tachyarrhythmias
  • Echocardiogram - if heart failure or cardiomyopathy is suspected 1

• Bone Density Testing

  • Consider in patients with prolonged hyperthyroidism due to risk of osteoporosis 5

• Ophthalmologic Examination

  • For patients with suspected Graves' ophthalmopathy
  • Includes exophthalmometry and assessment of extraocular muscle function 4

Diagnostic Algorithm

1. Initial Screening: TSH measurement

   • If TSH is suppressed, proceed to free T4 and free T3 testing

2. Confirm Hyperthyroidism: Low TSH with elevated free T4 and/or free T3

3. Determine Etiology:

   • Measure TSH receptor antibodies
     • If positive → Graves' disease
     • If negative → Proceed to thyroid imaging

4. Imaging Workup:

   • Thyroid ultrasound for all patients
   • RAIU scan if etiology remains unclear after antibody testing

Special Considerations

• Pregnancy: TRAb testing is essential for pregnant women with current or past Graves' disease to assess risk of fetal/neonatal thyrotoxicosis 1, 4

• Subclinical Hyperthyroidism: Defined as low TSH with normal free T4/T3; may require less aggressive workup but should still be evaluated, especially in elderly patients or those with cardiac symptoms 5

• Amiodarone-Induced Hyperthyroidism: Requires specialized testing to differentiate type 1 (iodine-induced) from type 2 (inflammatory) 2

Pitfalls to Avoid

• Relying solely on TSH without measuring free T4/T3
• Failing to test for thyroid antibodies, which are crucial for determining etiology
• Not considering radioactive iodine uptake testing when the diagnosis is unclear
• Overlooking non-thyroidal illness syndrome, which can affect thyroid function test results
• Neglecting to assess for complications of hyperthyroidism, particularly cardiac manifestations

By following this systematic approach to testing, clinicians can accurately diagnose hyperthyroidism, determine its etiology, and assess for complications, allowing for appropriate treatment selection and monitoring.