Diagnostic Approach for Hyperthyroidism

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 1
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
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 1, 2
Repeat abnormal TSH measurements for confirmation, especially if the initial TSH is between 0.1-0.45 mIU/L 2

Be particularly vigilant in screening high-risk populations, including elderly patients 1
Be particularly vigilant in screening high-risk populations, including post-partum women 1
Be particularly vigilant in screening high-risk populations, including patients with high levels of radiation exposure (>20 mGy) 1
Be particularly vigilant in screening high-risk populations, including patients with Down syndrome 1

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
For patients with TSH between 0.1-0.45 mIU/L, without these risk factors, repeat testing within 3 months 2
For patients with TSH between 0.1-0.45 mIU/L, 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 TSH <0.1 mIU/L and cardiac symptoms or arrhythmias, testing should be performed more urgently 2

Look for signs of atrial fibrillation, which is more common in hyperthyroid patients 3
Evaluate for pulmonary artery hypertension, which can occur in hyperthyroidism and lead to right ventricular dilatation 3
In patients with severe, long-standing hyperthyroidism, assess for heart failure despite the typically increased cardiac contractility 3
Consider bone mineral density testing in postmenopausal women with prolonged subclinical hyperthyroidism, as they are at increased risk for bone loss 2

Be aware that severe non-thyroid illness can lead to false positive TSH test results 1
Recognize that subclinical hyperthyroidism (low TSH with normal FT4/T3) is more common than overt disease in primary care populations 1
Avoid missing thyroid dysfunction in patients with Down syndrome, as some symptoms overlap with features of the syndrome 1
Remember that patients with known nodular thyroid disease may develop overt hyperthyroidism when exposed to excess iodine (e.g., radiographic contrast agents) 2

Hyperthyroidism is characterized by tremors, nervousness, insomnia, excessive sweating, heat intolerance, tachycardia, hypertension, and goiter, with treatment options including beta-blockers, antithyroid medications, radioactive iodine therapy, or surgery depending on the cause and severity, as recommended by the American College of Cardiology 4

Cardiovascular symptoms of hyperthyroidism include tachycardia, hypertension, palpitations, decreased systemic vascular resistance, increased cardiac output, and potential pulmonary artery hypertension, according to the American Heart Association 4, 5
Neurological symptoms of hyperthyroidism include tremors, nervousness, anxiety, hyperactivity, and insomnia, as noted by the American College of Cardiology 4
Dermatological symptoms of hyperthyroidism include excessive sweating, heat intolerance, and hair loss, as reported by the American Academy of Dermatology 4
Rare but serious manifestations of hyperthyroidism include heart failure in severe, long-standing cases, particularly with persistent tachycardia or rapid atrial fibrillation, as stated by the American Heart Association 6, 5

Beta-blockers, such as atenolol or propranolol, should be initiated promptly to control heart rate, reduce tremors, and mitigate cardiovascular complications in patients with hyperthyroidism, as recommended by the American College of Cardiology 4, 5
The goal of beta-blocker therapy is to lower heart rate to nearly normal, improving tachycardia-mediated ventricular dysfunction, according to the American Heart Association 5

Hyperthyroidism increases the risk of severe preeclampsia, preterm delivery, and heart failure in pregnant women, as noted by the American College of Obstetricians and Gynecologists 4
Cardiovascular complications are the chief cause of death after treatment of hyperthyroidism, especially in patients over 50 years, as reported by the American Heart Association 6, 5
Thyroid storm is a rare but life-threatening emergency that can occur in untreated hyperthyroidism, as stated by the American College of Cardiology 4