management of subclinical primary hypothyroidism in non-pregnant adults.

 RACGP position :

Main message

• Avoid routine thyroid function testing in well, asymptomatic, non-pregnant adults.
• Avoid routine treatment of subclinical hypothyroidism when:
  • TSH is mildly elevated, 4–10 mIU/L
  • FT4 is normal
  • patient is asymptomatic or symptoms are non-specific.

Definition

• Subclinical hypothyroidism is a biochemical diagnosis:
  • Elevated TSH
  • Normal free T4 / FT4
• It is not the same as overt hypothyroidism.

Typical hypothyroid symptoms

Symptoms may include:

• Fatigue
• Weight gain
• Constipation
• Dry skin
• Cold intolerance
• Low mood
• Menstrual change

However, these symptoms are common and non-specific, especially when TSH is only mildly elevated. Consider lifestyle, sleep, mental health, medications, alcohol, nutrition and other causes.

Do not do

• Do not screen asymptomatic non-pregnant adults for thyroid dysfunction.
• Do not order thyroid ultrasound for hypothyroidism unless there is:
  • palpable goitre
  • thyroid nodule
  • neck mass
• Do not repeat TPO antibodies if they have already been positive.
• Do not routinely treat asymptomatic subclinical hypothyroidism.
• Do not treat subclinical hypothyroidism with T3 / liothyronine.
• Do not routinely order FT3 or reverse T3 for assessment of hypothyroidism.

Initial approach to abnormal TSH

If TSH is elevated

• Check FT4.
• If FT4 is low, this suggests overt hypothyroidism.
• If FT4 is normal, this is subclinical hypothyroidism.

If TSH 4–10 mIU/L and FT4 normal

• Usually do not treat immediately.
• Repeat TSH and FT4 in 2–3 months to confirm persistence.
• Check TPO antibodies if not previously done.
• Review for:
  • symptoms
  • medications
  • recent illness
  • iodine exposure
  • lithium
  • amiodarone
  • immune checkpoint inhibitors
  • interferon
  • supplements such as kelp/iodine.

When to delay testing

• If the patient is acutely unwell, delay thyroid function testing.
• Acute illness can transiently alter TSH and give misleading results.

Monitoring

TSH 4–10 mIU/L, normal FT4, asymptomatic

• Monitor rather than treat.
• Repeat TFTs in 2–3 months.
• If stable and asymptomatic, continue observation.

Positive TPO antibodies

• Higher risk of progression to overt hypothyroidism.
• Repeat:
  • TSH and FT4 at 3 months
  • again at 6 months
  • then annually
• Start treatment if:
  • TSH progressively rises
  • symptoms develop
  • overt hypothyroidism develops.

When to consider treatment

Consider a trial of levothyroxine if TSH is 4–10 mIU/L, FT4 is normal, and there is one or more of:

• Symptoms suggestive of hypothyroidism
• Positive TPO antibodies
• Elevated cardiovascular risk
• Previous iodine treatment
• Previous thyroid surgery
• Other specific thyroid risk factors.

TSH greater than 10 mIU/L

• If TSH is >10 mIU/L on two separate tests 3 months apart, and the patient has symptoms of hypothyroidism, consider levothyroxine.
• Asymptomatic subclinical hypothyroidism with TSH >10 mIU/L is associated with higher risk of progression and cardiovascular events, so treatment may be considered depending on the clinical context.

Levothyroxine treatment principles

• Use levothyroxine, not T3.
• Recheck TSH after starting or changing dose.
• If symptoms improve and TSH normalises, continue and monitor.
• If TSH normalises but symptoms persist, consider:
  • stopping levothyroxine
  • monitoring TFTs
  • looking for another diagnosis.

Why not routinely treat?

Routine treatment may provide little or no clinical benefit for many patients with mild subclinical hypothyroidism.

Potential harms include:

• Medication burden
• Repeated monitoring
• Cost and resource use
• Overtreatment causing suppressed TSH
• Increased risk of:
  • atrial fibrillation
  • osteoporosis
  • fractures.

Thyroid ultrasound

Not indicated

• Subclinical hypothyroidism alone
• Abnormal TSH without palpable abnormality
• Fatigue or weight gain with normal neck examination

Indicated

• Palpable goitre
• Thyroid nodule
• Neck mass
• Suspicious structural thyroid finding.

Patient counselling script

“Your thyroid result shows a mildly raised TSH, but your thyroid hormone level is normal. This is called subclinical hypothyroidism. In many people it does not cause symptoms and does not need immediate treatment. We usually repeat the test in a few months to see if it persists, check thyroid antibodies if needed, and monitor over time. Starting thyroid medication too early can sometimes cause harm, especially if the dose suppresses the TSH too much.”

take-home points

• Subclinical hypothyroidism = raised TSH + normal FT4.
• Do not screen well asymptomatic adults.
• TSH 4–10 with normal FT4 usually means repeat and monitor, not automatic treatment.
• Repeat TFTs in 2–3 months to confirm persistence.
• Check TPO antibodies once if persistent mild elevation.
• Do not repeat TPO antibodies after a prior positive result.
• Do not order thyroid ultrasound unless there is goitre, nodule or neck mass.
• Do not use T3, FT3 or reverse T3 routinely.
• Consider levothyroxine if TSH >10, persistent, symptomatic, or higher-risk.
• Avoid overtreatment because suppressed TSH increases risk of AF, osteoporosis and fractures.