Primary hypothyroidism — Frequently asked questions (FAQ)
1) What is primary hypothyroidism?
Primary hypothyroidism results from the inability of the thyroid gland to produce adequate amounts of thyroid hormones. It is usually characterised by an elevated TSH level associated with reduced free T4, although subclinical forms with normal free T4 may also occur.
2) What are the most common causes?
In countries with adequate iodine intake, the main cause is autoimmune thyroiditis, also known as Hashimoto thyroiditis. Other causes include thyroid surgery, radioactive iodine treatment, neck radiotherapy, iodine deficiency and certain medicines such as amiodarone, lithium or interferon.
3) When should TSH and free T4 be requested?
Assessment is indicated in the presence of symptoms suggestive of thyroid dysfunction, goitre or thyroid nodules, infertility, menstrual irregularities, autoimmune diseases, lipid profile abnormalities, unexplained anaemia, growth delay in children or during pregnancy when risk factors are present.
4) How should an elevated TSH level be interpreted?
An elevated TSH level associated with reduced free T4 is compatible with overt primary hypothyroidism. When free T4 remains within the reference range, this indicates subclinical hypothyroidism, whose management depends on the degree of TSH elevation, the patient’s age and the clinical context.
5) What is the first-line treatment?
Levothyroxine is the treatment of choice. In young adults without cardiovascular disease, treatment may be started at a dose close to full replacement. In older adults or patients with heart disease, lower initial doses with gradual increases are recommended.
6) How should levothyroxine be taken?
Levothyroxine should be taken on an empty stomach, with water only, at least 30 to 60 minutes before breakfast, or at bedtime provided that at least 3 hours have passed since the last meal. Incorrect administration is one of the most common causes of inadequate control.
7) Which medicines can interfere with levothyroxine absorption?
Iron and calcium supplements, aluminium-containing antacids, sucralfate, cholestyramine, colestipol and ion-exchange resins can significantly reduce the intestinal absorption of levothyroxine. A minimum interval of 4 hours between administrations is recommended.
8) When should laboratory tests be repeated after starting treatment or changing the dose?
TSH should be reassessed approximately 6 to 8 weeks after starting treatment or after any dose adjustment. Once clinical and laboratory stability has been achieved, follow-up may be performed annually.
9) What should be done if symptoms persist despite a normal TSH?
Other causes of the symptoms should be considered, including nutritional deficiencies, associated autoimmune diseases, sleep disorders, depression, anxiety, fibromyalgia, chronic fatigue syndrome or other concomitant medical conditions.
10) When should referral to Endocrinology be considered?
Referral should be considered when there is persistent difficulty achieving euthyroidism, a need for high doses of levothyroxine, suspected malabsorption, pregnancy that is difficult to control, discordance between clinical findings and laboratory results or suspected complex thyroid disease.
11) Does hypothyroidism require lifelong treatment?
In most cases of permanent primary hypothyroidism, particularly when associated with autoimmune thyroiditis or following thyroid surgery, levothyroxine treatment is continued indefinitely. In some transient situations, treatment may be discontinued after specialist reassessment.
12) How should hypothyroidism be managed during pregnancy?
Pregnancy increases thyroid hormone requirements. Women with hypothyroidism should be monitored more frequently and often require levothyroxine dose adjustments to maintain appropriate TSH levels throughout pregnancy.
