LabMed

Toxic Adenoma

At a Glance

Toxic adenoma along with toxic multinodular goiter may be the leading cause of hyperthyroidism in countries in which iodine deficiency is common. Toxic adenomas produce elevated amounts of free thyroxine (fT4). The presenting symptoms of a toxic adenoma may be the same as the presenting symptoms for hyperthyroidism: heat intolerance, weight loss, increased appetite, tremor, and irritability.

What Tests Should I Request to Confirm My Clinical Dx? In addition, what follow-up tests might be useful?

The laboratory findings for toxic adenoma are that of hyperthyroidism. Generally, a diagnosis of hyperthyroidism is made when a pattern of low thyroid stimulating hormone (TSH) and elevated total triiodothyronine (T3) and fT4 is identified. Still, up to one-half of the patients with toxic nodules may show an elevated T3 but normal fT4. These findings may be taken into consideration along with imaging studies of radioactive iodine uptake.(Table 1)

Table 1.

Test Results Indicative of the Disorder
TSH free T4 total T3
<0.1 mclUnits/mL >1.8 ng/dL >181 ng/dL

Are There Any Factors That Might Affect the Lab Results? In particular, does your patient take any medications - OTC drugs or Herbals - that might affect the lab results?

Hospitalized patients may have transiently low or high TSH. Most frequently, TSH levels are suppressed during the acute phase of illness or during glucocorticoid or dopamine therapy. Other drugs like amiodarone can increase TSH levels. Critically ill euthyroid patients may be differentiated from hyperthyroid ill patients, because the latter show profoundly low TSH values less than 0.01 mU/L. Increases in T3 and T4 may occur with the ingestion of large quantities of exogenous thyroid hormone.

What Lab Results Are Absolutely Confirmatory?

Although no single lab test is absolutely confirmatory for toxic adenoma, the pattern of low TSH and elevated T3 and/or fT4 suggests hyperthyroidism and, in the presence of a clinically apparent enlarged nodule, is suggestive of toxic adenoma. These findings may be taken into consideration along with imaging studies of radioactive iodine uptake.

What Tests Should I Request to Confirm My Clinical Dx? In addition, what follow-up tests might be useful?

The errors in test interpretation for toxic adenoma are likewise by extension the errors in test interpretation for hyperthyroidism. The clinical setting must be considered when interpreting laboratory tests for hyperthyroidism. As mentioned, suppression of TSH may occur in ill, hospitalized patients, and pharmacotherapeutics can inflate TSH levels. Failure to treat toxic adenoma can result in ongoing symptoms of hyperthyroidism and long-term sequelae.

Are There Any Factors That Might Affect the Lab Results? In particular, does your patient take any medications - OTC drugs or Herbals - that might affect the lab results?

Amiodarone can increase TSH levels. Critically ill euthyroid patients may be differentiated from hyperthyroid ill patients, because the latter show profoundly low TSH values less than 0.01 mU/L. Increases in T3 and T4 may occur with the ingestion of large quantities of exogenous thyroid hormone.

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