Thyrotoxicosis Diagnostic Testing

Prioritize immediate assessment for delirium or altered mental status, seizure, atrial fibrillation, heart failure, thromboembolic disease, cardiovascular collapse, or severe systemic illness. These complications can accompany thyrotoxicosis; thyroid storm carries high mortality and warrants a high index of suspicion in a compatible presentation or risk setting. Obtain TSH, free T4, and free T3 while urgent stabilization and cause-directed assessment proceed. PubMedPubMedThyrotoxicosis - StatPearls - NCBI Bookshelf

Start biochemical testing with serum TSH. Thyrotoxicosis usually produces concordant elevation of T4 and T3 with suppressed TSH, and TSH is the recommended frontline screening test. Newly presenting Graves disease usually fully suppresses TSH to less than 0.05 mU/L; a low TSH of 0.1 to 0.4 mU/L should prompt consideration of alternative explanations for symptoms rather than presuming new Graves disease. PubMed+1PubMedDiagnosis and Treatment of Graves' Disease - Endotext - NCBI - NIHPubMedHow to interpret thyroid function tests

If TSH is suppressed, measure both free T4 and T3. T3 should be obtained when free T4 does not clearly verify suspected hyperthyroidism because T3 toxicosis may present with normal total T4 and free T4 but diagnostic T3 elevation. In acutely ill patients with low TSH but normal free T4 and normal T3, follow thyroid testing during recovery because some subsequently develop overt thyrotoxicosis. PubMedPubMedThyroid Function Tests - Clinical Methods - NCBI Bookshelf

After overt thyrotoxicosis is confirmed, seek clinical evidence of Graves disease: diffuse goiter, thyroid eye disease, and, less commonly, thyroid dermopathy increase its likelihood. Measure thyrotropin receptor antibodies (TRAb) or thyroid-stimulating immunoglobulins (TSI) when Graves disease is suspected. A positive TRAb or TSI result confirms Graves disease without further diagnostic testing. PubMed+1PubMedDiagnosis and Treatment of Graves' Disease - Endotext - NCBI - NIHthyroidGraves' Disease | American Thyroid Association

Prefer TRAb or TSI over thyroid peroxidase antibody testing for etiologic confirmation of Graves disease. TPO antibody testing alone is less useful for this decision, although absent TRAb with positive TPO antibodies can support a process more likely to resolve spontaneously in selected cases. PubMedPubMedTests for people with confirmed thyrotoxicosis - NCBI Bookshelf

If TRAb or TSI is negative, remember that Graves disease is not completely excluded. Proceed to thyroid uptake testing when the diagnosis remains uncertain and the result will distinguish Graves disease from autonomous nodular disease, thyroiditis, or exogenous hormone use. Scintigraphy has approximately 96% diagnostic accuracy, but Graves disease can show nonuniform or normal uptake in 5% to 12% of cases. Wiley+1WileyDiagnostic Options in Graves' or Non‐Graves' Thyrotoxicosis: A ...thyroidGraves' Disease | American Thyroid Association

Obtain a radioactive iodine uptake study or thyroid scan in thyrotoxic patients who lack clinical Graves features or whose antibody result does not establish the cause. In Graves disease, uptake is usually diffusely increased; nodules or fibrosis can alter this appearance. A diffuse goiter with thyroid eye disease and positive TRAb remains the most coherent Graves pattern even when scan appearance is atypical. PubMed+2PubMedThyrotoxicosis - StatPearls - NCBI BookshelfPubMedDiagnosis and Treatment of Graves' Disease - Endotext - NCBI - NIHWileyDiagnostic Options in Graves' or Non‐Graves' Thyrotoxicosis: A ...

A single toxic adenoma produces focal uptake within the autonomous nodule with suppression of uptake in surrounding thyroid tissue. Toxic multinodular goiter produces multiple focal areas of increased uptake with suppression of surrounding tissue; this pattern is often associated with older age, a nodular goiter, and an insidious presentation without eye signs. These high-uptake patterns indicate endogenous hormone overproduction and distinguish nodular autonomy from low-uptake thyrotoxicosis. PubMed+1PubMedThyrotoxicosis - StatPearls - NCBI BookshelfPubMedDiagnosis and Treatment of Graves' Disease - Endotext - NCBI - NIH

Low uptake redirects the workup away from hormone synthesis and toward destructive thyroiditis or exogenous thyroid hormone. In suspected factitious thyrotoxicosis, measure thyroglobulin: elevated T3/T4 with low TSH, low uptake, and low thyroglobulin supports exogenous thyroid supplement ingestion. Doppler ultrasonography may show reduced thyroid vascularization in this setting. PubMedPubMedThyrotoxicosis - StatPearls - NCBI Bookshelf

When total hormone results and the clinical picture diverge, repeat evaluation with free hormone measurements and review conditions that alter binding proteins. Pregnancy and exogenous estrogen raise thyroxine-binding globulin, increasing total T4 without necessarily increasing free T4; total hormone results should therefore not be interpreted as equivalent to free hormone excess in these settings. PubMedPubMedHow to interpret thyroid function tests

When a patient has a low TSH but free T4 and T3 are not elevated, do not equate the laboratory pattern with overt thyrotoxicosis. Acute nonthyroidal illness can produce this pattern, and repeat testing after recovery is appropriate when clinical suspicion remains. Conversely, obtain T3 in a patient with suppressed TSH and normal free T4 if symptoms or examination still suggest hyperthyroidism. PubMedPubMedThyroid Function Tests - Clinical Methods - NCBI Bookshelf

If a scan shows low uptake but the patient appears clinically hyperthyroid, specifically ask about prescribed levothyroxine, liothyronine, compounded thyroid preparations, weight-loss products, and supplements. A low thyroglobulin concentration materially strengthens the diagnosis of factitious thyrotoxicosis, whereas low uptake alone does not identify the source of hormone release. PubMedPubMedThyrotoxicosis - StatPearls - NCBI Bookshelf

In pregnancy or the postpartum period, use thyroid testing and etiologic assessment within pregnancy-specific guidance rather than applying nonpregnant total-hormone interpretation unmodified. Pregnancy increases thyroxine-binding globulin and can elevate total T4; free hormone measurements and the clinical context are therefore central to interpretation. thyroid+1thyroidAmerican Thyroid Association Guidelines for Diagnosis and Management of Thyroid Disease During Pregnancy Published in Thyroid Journal | American Thyroid AssociationPubMedHow to interpret thyroid function tests

Do not defer evaluation of clinically significant thyrotoxicosis in pregnancy. Untreated disease has been associated with pregnancy loss, pregnancy-induced hypertension, prematurity, low birth weight, intrauterine growth restriction, stillbirth, thyroid storm, and maternal congestive heart failure. Coordinate etiologic diagnosis and management with clinicians experienced in thyroid disease during pregnancy. thyroid+1thyroidAmerican Thyroid Association Guidelines for Diagnosis and Management of Thyroid Disease During Pregnancy Published in Thyroid Journal | American Thyroid AssociationthyroidVol 10 Issue 5 p.3-7 - American Thyroid Association