Workup for Hyperthyroidism
Initial Diagnostic Testing
Measure serum TSH first, followed by free T4 and free T3 if TSH is suppressed, to confirm biochemical hyperthyroidism. 1, 2
- TSH has sensitivity above 98% and specificity greater than 92% for detecting thyroid dysfunction 1
- Overt hyperthyroidism is defined as suppressed TSH with elevated free T4 and/or T3 2
- Subclinical hyperthyroidism shows suppressed TSH (typically <0.1 mIU/L) with normal free T4 and T3 2
Determining the Etiology
Once biochemical hyperthyroidism is confirmed, obtain TSH-receptor antibodies (TRAb) to distinguish Graves' disease from other causes. 3, 4
If TRAb is Positive:
- Graves' disease is confirmed (causes 70% of hyperthyroidism cases) 3
- Binding assays have 97.4% sensitivity and 99.2% specificity for Graves' disease diagnosis 4
- No further imaging is needed unless thyroid nodules are palpable 2
If TRAb is Negative or Etiology Unclear:
- Obtain thyroid scintigraphy (radioiodine uptake scan) to differentiate between causes 2, 3
- High uptake indicates autonomous thyroid function (toxic nodular goiter or toxic adenoma—16% of cases) 3
- Low or absent uptake indicates destructive thyroiditis (subacute thyroiditis—3% of cases) or exogenous thyroid hormone 3
- Thyroid ultrasonography can identify nodules and assess gland size 3
Additional Essential Testing
Obtain an ECG and cardiac evaluation for all patients with hyperthyroidism, as it causes atrial fibrillation, heart failure, and increased cardiovascular mortality. 1
- Initiate beta-blockers immediately for symptomatic tachycardia, palpitations, or cardiac symptoms 1
- Screen for concurrent adrenal insufficiency before treating hyperthyroidism, as thyroid hormone can precipitate adrenal crisis 1
Monitoring During Treatment
Monitor thyroid function tests (TSH, free T4) every 6-8 weeks during antithyroid drug titration. 1
- Check prothrombin time before surgical procedures, as antithyroid drugs may cause hypoprothrombinemia 5, 6
- Monitor complete blood count if patients develop sore throat, fever, or signs of infection (agranulocytosis risk) 5, 6
- Watch for hepatic dysfunction symptoms, particularly in the first 6 months of propylthiouracil therapy 6
Common Pitfalls to Avoid
- Never rely on free T4 alone—TSH must be suppressed to diagnose hyperthyroidism 2
- Do not skip TRAb testing—it distinguishes Graves' disease from other causes and guides treatment duration 3, 4
- Always obtain scintigraphy if TRAb is negative or nodules are present—this prevents misdiagnosis of thyroiditis as Graves' disease 2, 3
- Do not delay cardiac evaluation—hyperthyroidism causes serious cardiovascular complications requiring immediate management 1