Tests
1st tests to order
thyroid stimulating hormone (TSH)
Test
Initial screening test. Also used for follow up.
If not suppressed, toxic adenoma is essentially ruled out.[1] Do not order more tests until the results of the TSH test are available as a TSH value within the reference range excludes the majority of primary thyroid diseases.[22][23] If suppressed, thyroid hormone levels (triiodothyronine [T3]/thyroxine [T4]) should be measured.
In some cases of thyroid autonomy, TSH may be below the lower limits of normal for the assay but not completely suppressed.[1]
Confirms presence of thyroid dysfunction, but not its cause.
Result
suppressed
Tests to consider
free thyroxine (T4; or total T4 with a measure of binding)
Test
Elevated free T4 (or total T4 plus a measure of binding) confirms hyperthyroidism.
Free T4 may be normal in subclinical hyperthyroidism or in triiodothyronine (T3) toxicosis. If free T4 is normal, elevated T3 should be sought.
Confirms presence of thyroid dysfunction, but not its cause.
Result
elevated
total T3 with a measure of binding (or free T3)
Test
Total T3 with a measure of binding is considered to be the more reliable assay.
Elevated free T3 (calculated or assay) confirms hyperthyroidism.
Free T4 may be normal or elevated. Isolated elevation of free T3 occurs in T3 toxicosis.
If free T3 is normal, with a suppressed TSH and normal free T4, subclinical hyperthyroidism should be suspected.
Confirms presence of thyroid dysfunction, but not its cause.
Result
elevated
thyroid scan and uptake
Test
Typical appearance of hot nodule with suppression of surrounding thyroid tissue confirms toxic adenoma.[1][4][Figure caption and citation for the preceding image starts]: Hyperfunctioning thyroid nodule suppressing contralateral gland on thyroid scan (SSN = suprasternal notch)Arem R. Recurrent transient thyrotoxicosis in multinodular goitre. Postgrad Med J. 1990 Jan;66(771):54-6 [Citation ends].
I-123 is the preferred isotope. Tc-99 scan is less commonly used in the US because there is a risk of false-positive images and uptake cannot be measured.[21]
Result
hot nodule
thyroid ultrasound
Test
Should be obtained in all patients with known or suspected thyroid nodules.[24]
Do not order thyroid ultrasound as part of the initial investigations for hyperthyroidism if there is no palpable abnormality of the thyroid gland.[1][26]
Cold (i.e., nonfunctioning) or warm (i.e., isofunctioning) nodules >1 cm in diameter or with suspicious ultrasonographic characteristics (such as more-tall-than-wide shape, irregular margins, microcalcifications, increased vascularity, or marked hypoechogenicity) should be considered for further evaluation such as fine needle biopsy.[21][24]
In rare cases of hemorrhage into a toxic nodule associated with atypical scan findings, may show fluid in the nodule.
Result
nodule(s)
metabolic panel
Test
Findings are nonspecific.
Elevated alkaline phosphatase is generally of bony origin, due to increased bone turnover.
Most patients with hyperthyroidism will have elevated transaminases prior to initiating treatment and levels typically improve with antithyroid drug therapy.[27]
Result
may show: hypercalcemia; elevated aminotransferases or alk phos
CBC
Test
Findings are nonspecific. Baseline with differential is advisable before antithyroid drug treatment.
Mild neutropenia should not be regarded as a contraindication to use of antithyroid drug therapy and hyperthyroidism typically normalizes the neutrophil count.[28]
Result
may show anemia, leukocytosis
TSH receptor antibodies
Test
May be needed to differentiate toxic adenoma from Graves disease when the diagnosis is unclear and nuclear scan contraindicated.
Result
negative
thyroid peroxidase antibodies
Test
Sensitive but not specific for Graves disease.
Result
negative
ECG
Test
Hyperthyroidism, overt or subclinical (i.e., reduced serum TSH concentration but free T4 levels within reference ranges) is associated with increased risk of atrial fibrillation.[31]
Older adults may present with apathetic hyperthyroidism, such as atrial fibrillation alone.
Result
may show dysrhythmia
CT neck (noncontrast)
Test
Occasionally indicated for signs or symptoms of neck compression, or as part of preoperative evaluation before thyroid surgery.
Result
may delineate large goiter
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