What is the diagnostic plan for hyperthyroidism?

Diagnostic Plan for Hyperthyroidism

The diagnostic plan for hyperthyroidism should begin with measuring serum TSH, followed by free T4 and T3 levels if TSH is suppressed, and then determining the etiology through antibody testing and imaging studies. 1

Initial Laboratory Testing

• Measure serum thyroid-stimulating hormone (TSH) as the first-line test when hyperthyroidism is suspected, as it has high sensitivity (>98%) for detecting thyroid dysfunction 2
• If TSH is suppressed (<0.1 mIU/L), measure free thyroxine (FT4) and either total triiodothyronine (T3) or free T3 to confirm the diagnosis and determine severity 2, 3
• Values for serum TSH below 0.1 mIU/L are considered low, while those between 0.1-0.45 mIU/L may indicate subclinical hyperthyroidism 2
• Repeat abnormal TSH measurements for confirmation, especially if the initial TSH is between 0.1-0.45 mIU/L 2

Determining Etiology

• After confirming hyperthyroidism biochemically, determine the underlying cause through additional testing 4, 3
• Measure TSH-receptor antibodies to diagnose Graves' disease, which accounts for approximately 70% of hyperthyroidism cases 4, 1
• Measure thyroid peroxidase antibodies, which may be elevated in autoimmune thyroid disorders 4
• Perform thyroid ultrasonography to evaluate for nodules, goiter, or characteristic findings of thyroiditis 4, 3
• Conduct radioactive iodine uptake measurement and scan to distinguish between destructive thyroiditis and hyperthyroidism due to Graves' disease or nodular goiter 2, 5

Special Considerations for High-Risk Groups

• Be particularly vigilant in screening high-risk populations, including:
  • Elderly patients 2
  • Post-partum women 2
  • Patients with high levels of radiation exposure (>20 mGy) 2
  • Patients with Down syndrome 2
  • Patients with atrial fibrillation or other cardiac arrhythmias 1

Timing of Follow-up Testing

• For patients with TSH between 0.1-0.45 mIU/L:

  • If the patient has atrial fibrillation, cardiac disease, or other serious medical conditions, repeat testing within 2 weeks 2
  • Without these risk factors, repeat testing within 3 months 2
  • If TSH remains abnormal but stable, continue monitoring at 3-12 month intervals 2

• For patients with TSH <0.1 mIU/L:

  • Repeat measurement along with FT4 and T3 within 4 weeks 2
  • For patients with cardiac symptoms or arrhythmias, testing should be performed more urgently 2, 1

Evaluating for Complications

• Assess for cardiovascular complications, which are the chief cause of death in hyperthyroidism, especially in patients over 50 years 1
• Look for signs of atrial fibrillation, which is more common in hyperthyroid patients 1, 2
• Evaluate for pulmonary artery hypertension, which can occur in hyperthyroidism and lead to right ventricular dilatation 2
• In patients with severe, long-standing hyperthyroidism, assess for heart failure despite the typically increased cardiac contractility 2
• Consider bone mineral density testing in postmenopausal women with prolonged subclinical hyperthyroidism, as they are at increased risk for bone loss 2

Common Pitfalls to Avoid

• Do not rely solely on clinical symptoms for diagnosis, as they can be nonspecific and variable 3
• Be aware that severe non-thyroid illness can lead to false positive TSH test results 2
• Recognize that subclinical hyperthyroidism (low TSH with normal FT4/T3) is more common than overt disease in primary care populations 2
• Avoid missing thyroid dysfunction in patients with Down syndrome, as some symptoms overlap with features of the syndrome 2
• Remember that patients with known nodular thyroid disease may develop overt hyperthyroidism when exposed to excess iodine (e.g., radiographic contrast agents) 2