Thyroid disorders: reading the tests, and treating them

How are thyroid problems diagnosed?

Thyroid assessment starts with TSH — thyroid stimulating hormone — because the pituitary gland adjusts TSH very sensitively in response to small changes in thyroid hormone. When the thyroid underperforms, the pituitary pushes harder and TSH rises before free T4 has fallen below the reference range at all. That is why TSH moves first and is the right screening test, and why a normal TSH in an untreated patient makes significant thyroid disease unlikely.^[1]

What do an underactive and an overactive thyroid feel like?

The two conditions produce broadly opposite symptoms, though in practice the picture is often incomplete and easily mistaken for other things — which is why the diagnosis rests on the blood test rather than on the symptoms.

How is hypothyroidism treated?

Hypothyroidism is treated with levothyroxine, a synthetic form of the hormone T4, taken once daily. The dose is started according to age, weight and cardiac history, then adjusted by repeating TSH after six to eight weeks — no sooner, because the level takes that long to settle. Once stable, TSH is checked every six to twelve months, and after any change in dose, in pregnancy, or with significant weight change.

How the tablet is taken affects how well it works. Levothyroxine should be taken on an empty stomach, thirty to sixty minutes before breakfast, with water. Calcium and iron supplements, antacids, and to a lesser extent soya and coffee, reduce absorption substantially, and should be separated by at least four hours. A patient whose TSH will not come down despite dose increases is far more often taking the tablet with breakfast or with a calcium supplement than genuinely resistant to treatment.

Should mild (subclinical) hypothyroidism be treated?

This is one of the genuinely unsettled questions in the field, and the honest answer is that it depends. Where TSH is above 10 mIU/L, treatment is generally recommended, because progression to overt hypothyroidism is likely. Where TSH sits between the upper limit of normal and 10, the decision weighs several things: whether there are convincing symptoms, whether anti-TPO antibodies are positive (which makes progression more likely), the patient's age, whether there is cardiovascular disease, and — decisively — whether the patient is pregnant or planning pregnancy. In pregnancy the threshold for treating is much lower, because thyroid hormone is required for fetal brain development. In an asymptomatic 75-year-old with a TSH of 6, treatment is often not indicated at all.

What happens if a thyroid nodule is found?

Thyroid nodules are common and the great majority are benign. When one is found — on examination or incidentally on a scan — the questions are whether the thyroid is functioning normally, and whether the nodule has features that warrant a needle biopsy. Ultrasound answers the second: size, composition, echogenicity, margins, shape and the presence of microcalcifications together determine risk. Ultrasound is arranged with the specific question written on the request, and the report is used to decide between FNAC referral and simple interval monitoring. Bedside ultrasound at the consultation, which would allow that decision in a single visit, is planned at the clinic but not available at present.