What is the initial workup for a patient presenting with symptoms suggestive of hyperthyroidism?

Initial Workup for Hyperthyroidism

The initial workup for a patient with suspected hyperthyroidism should include measurement of serum TSH, free T4 (FT4), and free T3 (FT3) or total T3 to confirm the diagnosis and determine its severity. 1, 2

Step 1: Laboratory Testing

First-line Tests:

• TSH: The most sensitive initial test for thyroid dysfunction 3

  • Low TSH (<0.45 mIU/L) suggests hyperthyroidism
  • Very low TSH (<0.1 mIU/L) strongly indicates hyperthyroidism

• Free T4 (FT4): To confirm diagnosis and assess severity

  • Elevated FT4 with low TSH confirms overt hyperthyroidism

• Free T3 (FT3) or Total T3: Essential to detect T3 toxicosis

  • Some patients have normal FT4 but elevated FT3 (T3 toxicosis occurs in ~8-16% of hyperthyroid cases) 4

Additional Laboratory Tests:

• Complete blood count
• Serum electrolytes (including calcium and magnesium)
• Liver function tests
• Fasting blood glucose
• Lipid profile 5

Step 2: Determine Etiology

Once hyperthyroidism is biochemically confirmed, determine the underlying cause:

• Thyroid Antibody Testing:

  • TSH receptor antibodies (TRAb): Positive in Graves' disease
  • Thyroid peroxidase antibodies (TPOAb): Often positive in autoimmune thyroid disease 1, 2

• Thyroid Imaging:

  • Radioactive iodine uptake and scan: Distinguishes between destructive thyroiditis and hyperthyroidism due to Graves' disease or toxic nodular goiter 5
  • Thyroid ultrasound: Particularly useful if nodules are palpated or goiter is present 1

Step 3: Assess for Complications

• Cardiovascular Assessment:

  • ECG to detect arrhythmias, especially atrial fibrillation
  • Blood pressure measurement (often elevated systolic with normal/low diastolic)
  • Heart rate monitoring 2

• Bone Health Assessment (if chronic hyperthyroidism is suspected):

  • Consider bone mineral density testing, especially in postmenopausal women
  • Untreated subclinical hyperthyroidism can lead to bone loss 5

Step 4: Evaluate for Precipitating Factors

• Medication review (amiodarone, tyrosine kinase inhibitors, immune checkpoint inhibitors)
• Recent iodine exposure (contrast agents)
• Recent illness or stress
• Pregnancy status 2

Common Pitfalls to Avoid

1. Relying solely on TSH: While TSH is the most sensitive initial test, both FT4 and FT3 should be measured to confirm diagnosis and detect T3 toxicosis 4

2. Overlooking subclinical hyperthyroidism: Defined as low TSH with normal FT4 and FT3, which may still require monitoring or treatment depending on severity and patient factors 5

3. Missing non-thyroidal illness: Hospitalized patients may have abnormal thyroid function tests due to non-thyroidal illness rather than primary thyroid disease 3

4. Inadequate follow-up: For patients with subclinical hyperthyroidism (TSH 0.1-0.45 mIU/L), repeat testing within 3 months is recommended; for TSH <0.1 mIU/L, repeat within 4 weeks 5

5. Failure to recognize thyroid storm: A life-threatening condition requiring immediate treatment, characterized by extreme hyperthyroidism with systemic decompensation 6

By following this systematic approach, clinicians can efficiently diagnose hyperthyroidism, determine its cause, and assess for complications that may influence management decisions.