Low TSH and high T4: is this hyperthyroidism?

If your TSH is low and your T4 or T3 is high, your body has more thyroid hormone than it needs. Doctors call this overt hyperthyroidism, or more broadly thyrotoxicosis. It is very treatable, but it should not be ignored, because too much thyroid hormone strains the heart and bones. You can check your numbers with the thyroid report reader.

What does this pattern mean?

Thyroid hormone sets the speed of your metabolism. When there is too much, everything runs fast. The pituitary gland senses the excess and switches TSH off, which is why TSH is low or even undetectable. Sometimes only T3 is high while T4 is normal, called T3 toxicosis, which is seen in early Graves’ disease and overactive nodules.

If TSH is low but T4 and T3 are still normal, the picture is milder. Read low TSH with normal T4.

What symptoms can it cause?

• a fast or pounding heartbeat
• weight loss despite a good appetite
• feeling hot, sweating, and disliking warm weather
• tremor of the hands
• anxiety, irritability and poor sleep
• loose motions or frequent bowel movements
• muscle weakness, especially climbing stairs
• lighter or fewer periods
• thinning of hair. Read hair loss and the thyroid.

Older people may have few of these and instead feel tired, lose weight or develop an irregular heartbeat.

What causes it?

• Graves’ disease. An autoimmune condition where antibodies (TRAb) switch the thyroid on. It is the most common cause, especially in younger women. It can also affect the eyes, making them bulge, water or feel gritty.
• Toxic nodules or a toxic multinodular goitre. One or more lumps in the thyroid make hormone on their own, more common in older adults. Read what happens after a thyroid nodule is found.
• Thyroiditis. Inflammation of the thyroid makes it leak stored hormone. It can follow a viral illness (often with a painful neck), childbirth, or some medicines. It is usually temporary.
• Too much thyroid medicine, or thyroid hormone hidden in some weight-loss products.
• Iodine excess, from contrast dyes or some supplements.

Some lab results only look overactive. Biotin in hair and nail supplements can make TSH read low and T4 read high when the thyroid is actually normal. Always mention supplements to your doctor.

How do doctors find the cause?

The cause decides the treatment, so this step matters. Depending on your situation, your doctor may order:

• TSH receptor antibodies (TRAb), which confirm Graves’ disease
• A thyroid scan (technetium or iodine uptake), which shows whether the gland is overactive or leaking hormone
• A thyroid ultrasound, if there is a lump or swelling
• ESR or CRP, if the neck is painful and thyroiditis is suspected

How is it treated?

Treatment depends on the cause, your age and your preferences. Your doctor will discuss:

• Beta blockers, such as propranolol, to calm the fast heartbeat and tremor while the main treatment starts working.
• Anti-thyroid medicines. Carbimazole or methimazole are the usual choice in India. Propylthiouracil (PTU) is used mainly in early pregnancy. For Graves’ disease these are often continued for one to two years, and some people stay in remission afterwards.
• Radioactive iodine, a one-time drink or capsule that slowly shrinks the overactive tissue. It is common for toxic nodules and for Graves’ disease that comes back. It is not used in pregnancy.
• Surgery to remove part or all of the thyroid, for large goitres, suspicious nodules, or when other options are not suitable.

Thyroiditis usually needs only symptom relief, because it settles in weeks to months. It is often followed by a temporary underactive phase.

What side effects should I watch for on anti-thyroid medicines?

Most people tolerate them well. Rash and itching are the commonest side effects. Rarely, these medicines can lower the white blood cells that fight infection, a condition called agranulocytosis, or affect the liver. If you develop fever, a sore throat or mouth ulcers while on these medicines, contact your doctor immediately. If you cannot reach your doctor, go to a hospital emergency department today and ask for a blood count (CBC). A low white cell count can lead to a serious infection within hours, so this cannot wait until your next appointment.

The American Thyroid Association guideline advises that people on anti-thyroid medicines should be told, before starting and at each visit, to stop the medicine and contact their doctor straight away if they develop symptoms that suggest agranulocytosis, such as fever or a sore throat, until a blood count shows it is safe. — Summarised from: American Thyroid Association hyperthyroidism guideline 2016 (Ross DS et al., Thyroid 2016, PMID 27521067)

Ask your doctor at the start of treatment exactly what to do if this happens. Yellow eyes, dark urine, pale stools or severe tiredness also need urgent review, as they can point to liver injury.

What about pregnancy?

An overactive thyroid needs careful planning before and during pregnancy, as the choice of medicine changes. Read thyroid problems in pregnancy and discuss your plans with your doctor early.

What should you ask your doctor?

• What is the cause of my overactive thyroid?
• Which treatment suits me best, and how long will it take?
• Do I need an ECG or eye check?
• What should I do if I get fever or a sore throat on these medicines?

Hyperthyroidism is best managed with an endocrinologist. See who an endocrinologist is or book a consultation.