May represent early stages of thyroid disease. If the patient is asymptomatic, the first action should always be to repeat the tests to exclude lab error.
Low TSH with normal T4/T3: Repeat within a fortnight. If stable, in a young patient repeat at 3 – 6 months and then annually; in an older patient follow up more closely due to AF risk. If due to Graves’ disease (check receptor autoantibody) then may spontaneously remit and has slow rate of progression. Toxic multinodular goitre has faster rate of progression and early intervention is usually advised.
Effects: One study showed a 3 x increase in risk of AF compared to euthyroidism, and another showed an increase in all-cause mortality. Not known whether it increases osteoporosis risk (known to do so if iatrogenic, but not known whether non-iatrogenic has same effect). There is, however, no evidence that any sort of early treatment can prevent these problems.
High TSH with normal T4/T3: Associated with increased risks CAD and fetal loss/stillbirth. There is no evidence that treatment with a TSH <10 in an asymptomatic patient is beneficial, although it may be indicated in a patient who has goitre or who wishes to become pregnant.
- Acute intercurrent illness can affect TFTs even in the absence of thyroid problems.
- In treated hyperthyroidism, the TSH suppression can take a while to recover, giving a temporary result of low TSH with normal thyroid hormones for a while after treatment starts.
(From the BMJ educational module on abnormal TFTs in the well patient)