Underactive thyroid (hypothyroidism): symptoms, causes and testing

An underactive thyroid, in medical terms hypothyroidism, means your thyroid makes too little hormone. As a result many processes slow down: you burn energy more slowly, tire more easily and often feel cold. It is the most common thyroid disorder, and occurs more often in women and at older age (Chaker 2017).

This article expands on the overview about your thyroid, focusing on the underactive side.

What is an underactive thyroid?

With an underactive thyroid, production of T4 and T3 is too low. Your pituitary responds by raising TSH. So hypothyroidism typically shows a high TSH with a low or low-normal free T4. When TSH is mildly raised while free T4 is still normal, it is called subclinical hypothyroidism, and not everyone needs treatment (Biondi 2019).

Which symptoms fit an underactive thyroid?

• Tiredness and a sluggish feeling
• Unexplained weight gain
• Feeling cold when others do not
• Dry skin, hair loss and brittle nails
• Constipation
• Low or flat mood
• Trouble concentrating

What are the causes?

The most common cause is Hashimoto's, an autoimmune process. Other causes include iodine deficiency, previous thyroid surgery or radiation, certain medicines, and the period after pregnancy.

Which blood values give insight?

To understand your TSH number, read on about your TSH level, about thyroid antibodies, or about thyroid and fatigue.

What can you do?

An underactive thyroid is easy to follow with blood testing. To measure your values without a referral, you can have a thyroid function test at Vitalcheck. If your TSH is raised, discuss the result with your GP before changing anything yourself.

References

• Chaker L, et al. Hypothyroidism. Lancet. 2017. PMID: 28336049.
• Biondi B, Cooper DS. Subclinical Hypothyroidism: A Review. JAMA. 2019. PMID: 31287527.
• NHG-Standaard Schildklieraandoeningen. Dutch College of General Practitioners.

Every blood test result includes a professional assessment from a BIG-registered doctor. For treatment decisions, discuss your results with your GP.