Adult thyroid disorder testing algorithm, a flowchart for thyroid testing

Do not screen asymptomatic patients

Current evidence is insufficient for screening asymptomatic adults. Screening benefits high risk subgroups, for example, personal or family history of thyroid disorder, amiodarone, lithium treatment, autoimmune disease.

Only use thyroid ultrasound for visible or palpable nodules or goitre

Thyroid ultrasound is indicated to assess visible or palpable thyroid nodules or goitre found during clinical examination. Ultrasound is not indicated to investigate hypothyroidism or positive antithyroid antibodies.

TSH

TSH is the most appropriate initial investigation for suspected primary thyroid disorder. Free T4 and/or free T3 are not usually requested in isolation. If you suspect pituitary disorder, request both TSH and free T4 on laboratory form initially, as it is essential to interpret TSH in the context of a free T4 measurement.

For patients with suspected primary thyroid disorder, there are three further options, based on the patient’s TSH levels.

If TSH is normal

No further testing. The algorithm ends here for these patients.

Request free T4. Further investigation lead to two further options based on T4 levels.

If T4 is normal, this is subclinical hypothyroidism

Subclinical thyroid disorder identified by testing requires careful clinical assessment of relevant symptoms, thyroid morphology and important comorbidities. Further options depend on TSH levels.

If TSH is equal to or less than 10 mIU/L

Measure TSH, T4, TPO antibodies in 2 to 3 months.

If patient is symptomatic, offer a 3 to 6-month trial of levothyroxine treatment without any antibody testing

After 2 to 3 months, if TSH, T4 normal, TPO negative

No further testing. The algorithm ends here for these patients.

After 2 to 3 months, if TSH is equal to or less than 10 mIU/L AND TPO is negative

Measure TSH and T4 yearly. Algorithm ends here for these patients.

After 2 to 3 months, if TSH is equal to or less than 10 mIU/L AND TPO is positive

Based on patient preference and symptoms, either prescribe levothyroxine treatment or measure TSH and T4 yearly. Algorithm ends here for these patients.

If TSH is greater than 10 mIU/L

Prescribe levothyroxine treatment. Measure TSH and T4 for dose adjustment at 6 to 8 weeks. Once stable and in normal range, measure TSH yearly. Algorithm ends here for these patients.

If T4 is low, this is overt hypothyroidism

Prescribe levothyroxine treatment. Measure TSH and T4 for dose adjustment at 6 to 8 weeks. Once stable and in normal range, measure TSH yearly. Algorithm ends here for these patients.

Measure T4. If TSH is less than 0.1 mIU/L, also measure T3. Further investigation lead to two further options based on T4 and/or T3 levels.

If T4 and/or T3 is normal and TSH is less than 0.1 mIU/L, this is subclinical hyperthyroidism

Subclinical thyroid disorder identified by testing requires careful clinical assessment of relevant symptoms, thyroid morphology and important comorbidities. Further options depend on TSH levels.

If TSH is equal to or greater than 0.1 mIU/L

Measure TSH and T4 in 4 to 8 weeks. If both normal, no further testing. Algorithm ends here for these patients.

If TSH is equal to or greater than 0.1 mIU/L and T4 normal

Repeat testing every 6 to 12 months. Algorithm ends here for these patients.

If TSH is less than 0.1 mIU/L

Refer patient to endocrinologist. Algorithm ends here for these patients.

If T4 and/or T3 are high, this is overt hyperthyroidism

Further options depend on TRAB measurements and further testing.

Measure TRAB

if positive, indicates Graves disease.

Other tests may be indicated if subacute thyroiditis, post-partum thyroiditis or amiodarone thyroid dysfunction is suspected. Suggest discussing with endocrinologist.

Prescribe antithyroid treatment, and refer to endocrinologist

Measure T4, T3 and TSH every 4 weeks. Monitoring depends on clinical situation, for example, some patients reach hypothyroid state quickly, and need frequent measurement. Algorithm ends here for these patients.

Note: In subacute thyroiditis, antithyroid treatment is contraindicated.

Developed based on 2017 Royal College of Pathologists of Australasia. Position statement: Thyroid function testing for adult diagnosis and monitoring, with input from experts: Associate Professor Shane Hamblin, Melbourne and Professor Rita Horvath, Sydney. Endorsed by the Endocrine Society of Australia.

• TSH = thyroid-stimulating hormone
• T4 = free thyroxine
• T3 = free triiodothyronine
• TPO = thyroid peroxidase
• TRAB = TSH receptor antibodies