Hypothyroidism: Symptoms, TSH Testing and Starting Treatment
Hypothyroidism is one of the most common endocrine conditions and one of the most frequently mis-attributed. Its symptoms are the symptoms of ordinary modern life, which is why diagnosis depends on a blood test rather than on how someone feels.
What the thyroid does
The thyroid gland sits at the front of the neck and produces thyroxine, called T4, and a smaller amount of the more active triiodothyronine, T3. These hormones set the metabolic rate of nearly every tissue.
The pituitary gland monitors the level and releases thyroid stimulating hormone, TSH, to push the thyroid harder when levels fall. This is why TSH goes up when the thyroid is underactive, which strikes many people as backwards the first time they see a report.
Symptoms
- Fatigue and daytime sleepiness
- Weight gain, usually modest, with difficulty losing weight
- Cold intolerance
- Dry, coarse skin and brittle nails
- Hair thinning, including loss of the outer third of the eyebrows
- Constipation
- Low mood, poor concentration and memory complaints
- Muscle aches, cramps and weakness
- Heavy or irregular periods, and reduced fertility
- Hoarse voice
- Puffiness around the eyes and face
- Slow heart rate
- Carpal tunnel syndrome
- Raised cholesterol on a routine test
Severe untreated hypothyroidism can progress to myxoedema, with marked slowing, low body temperature and confusion, which is a medical emergency.
Causes
- Autoimmune thyroiditis, also called Hashimoto’s disease, the commonest cause where iodine intake is adequate
- Iodine deficiency, still relevant in some regions despite salt iodisation
- Previous thyroid surgery or radioactive iodine treatment
- Neck radiotherapy
- Medications: lithium, amiodarone, some immunotherapies, and excessive iodine
- Congenital hypothyroidism, screened for at birth
- Pituitary disease, which causes central hypothyroidism with a low or inappropriately normal TSH
- Postpartum thyroiditis, often transient
Reading the tests
The first-line test is TSH. If abnormal, free T4 is added.
- High TSH with low free T4: overt primary hypothyroidism
- High TSH with normal free T4: subclinical hypothyroidism
- Low or normal TSH with low free T4: suggests pituitary or hypothalamic disease, needing specialist referral
- Anti-TPO antibodies identify autoimmune cause and predict progression
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Reference ranges vary between laboratories and change in pregnancy, so compare against the range printed on your own report. Routine T3 testing is not useful in diagnosing hypothyroidism.
Note that TSH can be transiently abnormal during any significant illness, so recheck after recovery before committing to lifelong treatment.
Subclinical hypothyroidism
This is the common grey zone. Treatment is generally considered when TSH is above 10 mIU/L, when anti-TPO antibodies are positive, in pregnancy or when planning pregnancy, when there is goitre, or when symptoms are clear and a trial is agreed. For a mildly raised TSH with no antibodies and no symptoms, repeating the test in three months is often the right first step, because many normalise on their own.
Treatment
Levothyroxine, a synthetic T4, is the standard treatment and is highly effective. How it is taken matters as much as the dose.
- Take it on an empty stomach, 30 to 60 minutes before breakfast, or at bedtime at least three hours after the last meal
- Take it at the same time daily, with water
- Separate by at least four hours from calcium, iron, magnesium, multivitamins, antacids and some cholesterol binders, all of which block absorption
- Coffee, soy and high-fibre meals also reduce absorption, so leave a gap
- Do not switch brands casually; formulations differ slightly in absorption
- Do not stop because you feel better. The improvement is the treatment working
Starting doses are lower in older people and in anyone with heart disease, and are increased gradually.
Monitoring
Recheck TSH six to eight weeks after starting or changing a dose, since the level takes that long to stabilise. Earlier testing produces misleading numbers and unnecessary dose changes. Once stable, annual testing is usually enough.
In pregnancy, requirements rise early, often by 25 to 30 percent, and testing is needed every four weeks in the first half. Untreated hypothyroidism in pregnancy affects fetal brain development, so it should never be left unmanaged.
Over-treatment
Too much levothyroxine produces palpitations, tremor, anxiety, insomnia, weight loss and heat intolerance, and over years it increases the risk of atrial fibrillation and bone loss. A suppressed TSH on treatment should prompt a dose reduction, not reassurance.
What does not help
T3-containing and desiccated thyroid preparations are not first-line and have inconsistent evidence. Iodine supplements do not treat autoimmune hypothyroidism and can worsen it. No diet, including gluten-free eating in the absence of coeliac disease, has been shown to reverse established autoimmune hypothyroidism.
This is general information. Dose, timing and whether to treat a borderline result are individual decisions for your doctor.