Is the test of any use?

I am often asked this question and this article represents my personal point of view as a pathologist working in health screenings for many years. The answer is a qualified yes.

Who are you testing for?

A wide range of people of different ages are at risk for thyroid disease, so it is difficult to give precise advice on a suitable age range for testing, but in general young and middle-aged people, especially, but not exclusively, women are at the highest risk. People without symptoms can be tested, as an underactive thyroid may show no symptoms in the early stages (subclinical hypothyroidism), and if these general symptoms are present, testing may be advisable; Excessive tiredness, unexplained weight gain, dry skin, constipation, or depression.

What is the thyroid exam?

Screening usually means testing normal people without symptoms to see if they harbor an undisclosed disease. With thyroid testing, it is often people with symptoms, often vague symptoms, who present for testing. Screening for thyroid diseases in normal people is not carried out in an organized manner equivalent to, for example, breast or bowel screening. The thyroid test involves a simple blood test. It is common to start with a very effective test, the thyroid stimulating hormone (TSH) test. A person showing symptoms that point to thyroid disease may be recommended to undergo a panel of tests that includes TSH, but this would not really be a screening test, but more according to diagnostic tests. Therefore, for routine tests, it is recommended to do the TSH blood test first and then decide whether to perform further tests based on the result. TSH is the hormone produced by the pituitary gland at the base of the brain that drives the thyroid gland in the neck to produce thyroxine (T4) and triiodothyronine (T3). T3 and T4 enter the bloodstream and control the rate of cellular metabolism. Too little hormone and cellular metabolism slows down, leading to weight gain, fatigue, and other general health effects. Too much T3 and T4 cause cellular metabolism to increase and energy to burn rapidly, resulting in hyperactivity and weight loss. The thyroid test leans toward detecting an underactive thyroid rather than an overactive one, although the TSH test will show an abnormal result in both situations.

What do your results mean?

The normal level of thyroid stimulating hormone (TSH) is between 0.35 and 5.5. A normal result is very reassuring. It is unusual for TSH to be normal when the thyroid is underactive, but this can happen rarely. It is for this reason that a person with symptoms strongly suggesting an underactive thyroid would be recommended to have a panel of tests done to exclude rare conditions such as pituitary gland disease.

The TSH test is most often performed on a serum sample. Serum is obtained from a blood sample by spinning the blood very quickly in a centrifuge so that the red blood cells are thrown to the bottom of the sample tube. The yellow serum is placed on top of the red blood cells and is removed for analysis, leaving the red blood cells in the sample tube. Some newer TSH tests are designed to use whole blood that has not been centrifuged. This has the advantage that the test does not have to be performed in a sophisticated laboratory, but can be performed quickly in a clinic or doctor’s office. However, the test samples are slightly different and the results may not always be directly comparable. However, as a tool to look for early signs of disease, the whole blood test is very convenient and can increase access to testing.

An abnormal TSH result where the TSH level is high, above 5.5, suggests that the thyroid is underactive. This must be confirmed by other tests and further tests are carried out to identify the cause. Additional tests in this situation would include thyroxine (T4) and triiodothyronine (T3) measured from a serum sample. Of course, since these are the hormones that are missing when the thyroid is underactive, the results would be low for these hormones.

It is understandable that when the results of these tests are equivocal, for example TSH is slightly high but T3 and T4 are normal, a definitive diagnosis is not possible. A situation like this can occur when there are few or no symptoms of disease and, for lack of a better term, this condition is labeled “subclinical hypothyroidism.”

How to get a TSH blood test

You can take a blood sample to test yourself using a fingerstick sample (capillary blood) or have someone take a blood sample from your arm (venous blood). Self-sampling is easy and convenient.