Subclinical Hypothyroidism (SCH)
Subclinical Hypothyroidism is a condition when blood levels of TSH (Thyrotropin) are high, but levels of free T4 (Thyroxine) are normal. The term “subclinical” implies that the disease is present without obvious symptoms. However, this can also indicate an early stage of the disease, much like early diabetes, heart disease or dementia, before overt symptoms develop.
Studies have shown TSH levels rise (usually <8 mU/L) in healthy older people (>65 years) who do not have thyroid disease. In these people, the higher TSH levels may even be protective. However, while higher TSH was protective, higher levels of T4 was harmful. Therefore treating them with thyroid hormones to increase T4 levels may not be beneficial. (1) Ref (2) Ref
Heart Disease Risk
Studies done in people younger than 60 years have shown that having subclinical hypothyroidism is associated with worse heart function, particularly in relation to heart pumping. This was worse in women and in those with positive thyroid antibodies. (3) Ref
Some of you have told me that your doctor has refused to change your thyroid hormone dose because you either have heart disease, or you are at higher risk for it. Interestingly, Dr. Salman Razvi from the UK says that though there is data to indicate benefits, large scale studies to test thyroid hormones in patients with heart disease have been hampered by physician beliefs.
One explanation for this is the common belief of physicians that exogenous thyroid hormone (or its analogues) therapy in cardiac patients could precipitate the development of arrhythmia, myocardial ischemia/ infarction, or worsening of congestive heart failure.Dr. Salman Razvi
Hypothyroidism is the commonest cause of high cholesterol. Therefore it is important to look into it when deciding treatment options for SCH.
What About Women Planning Pregnancy?
Pregnancy and hypothyroidism deserve a separate post. Here I will briefly mention that if you are planning a pregnancy, it is worthwhile to postpone pregnancy or infertility treatment until your TSH levels are at the American Thyroid Association recommended level of <2.5 mU/L. (5) Ref
What Do I Recommend?
1) Get the right tests done.
Checking only TSH or TSH and Total T3, Total T4 is not enough. You need to do a complete thyroid profile (more on testing later), which includes levels of free hormones as well as Anti-TPO and Anti Thyroglobulin antibodies.
2) Repeat tests.
Do the thyroid function tests again if your TSH is mildly raised and you do not have major symptoms or risk factors or you are not planning a pregnancy.
3) Check for nutritional depletion
The major nutrients are iron levels, vitamin D3, B12, zinc and selenium. (Doing only a CBC with Haemoglobin does not give us the complete picture of your iron status).
Repeat lab tests after correcting nutrient depletions.
4) Drugs That May Impact Thyroid Function
If you are being treated with Lithium, Amiodarone, Iodine or Interferons (there are more drugs) your thyroid function may be affected.
5) Wait and watch , particularly in older people.
6) Treatment with thyroid hormones in people with subclinical hypothyroidism.
Treating with thyroid hormones is justified if you are younger than 65 years of age and have
- Significant hypothyroid symptoms.
- Positive thyroid antibodies
- TSH levels are gradually rising, particularly after correcting nutrient depletions and stopping gluten. containing food.
- You are planning a pregnancy.
7) How often should you repeat thyroid function tests (TFT)?
If treatment has been initiated, then repeating TFT in 6-8 weeks is necessary to know the correct dosage. Once you are stabilized at a certain dose to achieve optimal hormones levels, testing every 3-6 months may be okay. However, testing more frequently may be required if you have lost a considerable amount of weight. Otherwise, you may be at risk of becoming hyperthyroid or have an over-suppressed TSH. Both of these are not good for you!
8) In older people, a higher TSH cutoff level may be required.
In older people un upper level of TSH of 5 or 6 mU/L may be fine.
9) What about Thyroid hormone levels in younger people?
This question requires a deeper dive, because each one of you may have a certain ‘thyroid set-point” which is decided by several factors, genes being one of them.
Most of you on thyroid hormones may feel good at a TSH level of 2-2.5 mU/L and corresponding Free T4 and Free T3 levels. Some of you may need individualized management from a provider who has advanced training in treating hypothyroidism.