When to start treatment for primary hypothyroidism in adults
Primary hypothyroidism is treated with thyroxine replacement therapy (levothyroxine), with the aim of achieving euthyroidism and symptom relief. The decision to treat depends primarily on:
- whether the patient has overt or subclinical disease
- whether the patient is symptomatic
- the degree of thyroid stimulating hormone (TSH) elevation.
Overt symptomatic primary hypothyroidism is a clear indication to start treatment with levothyroxine. Testing for serum thyroid peroxidase antibodies is not essential as it does not affect the decision to start treatment.
Overt asymptomatic primary hypothyroidism is rare—it sometimes occurs following recent critical nonthyroidal illness. Before starting treatment, confirm that the illness is persistent by repeating the test after 4 to 8 weeks (or sooner if symptoms develop).
Subclinical symptomatic primary hypothyroidism (even if serum TSH concentration is only mildly elevated) is a reasonable indication to trial therapy to relieve symptoms.
Subclinical asymptomatic primary hypothyroidism with a serum TSH concentration above 10 milliunits/L indicates a high risk of progression to overt disease. Retest the serum TSH concentration after 4 to 8 weeks, and start treatment if hypothyroidism is persistent.
Subclinical asymptomatic hypothyroidism with mildly elevated serum TSH concentration (in the range 4 to 10 milliunits/L) may not require treatment. Retest the serum TSH concentration after 4 to 8 weeks to confirm the hypothyroidism is persistent, and also test for thyroid peroxidase antibody. Patients with a positive thyroid peroxidase antibody are more likely to progress to overt hypothyroidism—repeat thyroid function tests after 3 months, then 6- to 12-monthly thereafter. Start treatment if the patient has a progressive rise in TSH or if symptoms occur. Patients with a negative thyroid peroxidase antibody can be assessed less frequently (eg every 12 months).
Hypothyroidism (including subclinical hypothyroidism) increases the incidence of cardiovascular risk factors (eg hypercholesterolaemia, elevated blood pressure), particularly in patients diagnosed at a young age (eg less than 60 years) and with higher serum TSH concentrations. In a young patient with hypothyroidism who does not meet other criteria for treatment, but who has a significant cardiovascular risk factor, consider a 3- to 6-month trial of levothyroxine. Stop treatment if a clear improvement does not occur (eg reduced low-density lipoprotein [LDL] concentration), and continue monitoring serum TSH concentration.