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Borderline thyroid tests: When should you take thyroid medication?

January 27, 2011 51 Comments by Scott Isaacs MD

A recent study found that many people have untreated thyroid disease.  The study, published in the Journal of Medical Screening assessed over 4000 people between the ages of 50 and 65 and found about 8% have low thyroid levels.  When weight goes up, many people suspect a low thyroid.  But when they go to the doctor, they get the routine “TSH” test and are told “it is borderline” and probably not the problem.  As an endocrinologist, I see this frequently.  There are so many cases with borderline thyroid testing where the thyroid really was to blame.  Once treated, thyroid patients lose a lot of weight without a major change in their diet or exercise routine.

Thyroid experts recognize the TSH test as the test of choice when thyroid disease is suspected.  An elevated TSH test diagnoses hypothyroidism.  TSH is more sensitive than other thyroid tests because it begins to rise before thyroid hormones drop.  As such, it’s a better indicator of early thyroid dysfunction.

When the TSH test is “high normal,” in the range of 2.5-4.5, deciding to take thyroid medication can be a difficult decision.  I’ve seen many patients with this situation.  Frequently, thyroid tests in this range will normalize within a few months, other times, they progress to overt hypothyroidism.   The first step is to repeat the test.  I never make a treatment decision based on a single blood test.  Experts recommend waiting 3 months to repeat a borderline abnormal TSH test, but if you have a lot of symptoms it is better to do it sooner.

In my opinion, many doctors take the easy way out and prescribe a low dose of thyroid medication when the thyroid is really normal.   If you take low dose thyroid hormone and your thyroid is normal, it will make fewer hormones to maintain normal levels.  So taking a low dose of thyroid hormone, even if you don’t need it may not do much.  I’ve seen so many patients who have tried this approach and then come to me still complaining of symptoms.  Some of these patients stopped thyroid hormone replacement and felt better.  Others do feel better, but I have always wondered how much of this was placebo effect?  A study was done to determine if treatment with thyroid hormone could improve the symptoms of hypothyroidism in people with normal thyroid function tests.  The results, published in the British Medical Journal, showed that thyroid hormone was no more effective than placebo for relieving symptoms.

On the other hand, some people with borderline tests have early thyroid disease that is certain to progress.  Diagnosing hypothyroidism in the early stages can be tricky.  That’s because when the thyroid starts to fail, tests can remain in the normal range for a period of time.  The first thing that indicates low thyroid is an elevated TSH level.  A change from a low normal TSH to a high normal TSH over a period of a few months may mean early thyroid failure.  If thyroid antibodies are positive or if the thyroid gland is enlarged the risk for thyroid failure is extremely high.  If the thyroid antibodies are normal and the thyroid is not enlarged, the risk is much lower.

The bottom line is that many times there is no easy answer.  If the thyroid is truly to blame, tests will become more clearly defined as time goes on.  There is usually no harm in waiting a few months to make a decision about treatment.

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51 Comments

  1. Laura says:
    Tuesday, March 25, 2014 at 1:40pm

    I have had my TSH checked over the last 5 years as part of my physical it is everything from 4.80 – 7.6, they also looked at my T4 twice which was still in a normal range. My question is do you see variability in TSH level, seems like it is all over the place up and down in the range started above? I am 54 and post menopausal, having symptoms like fatigue, depression, brain fog, decreased libido, loss of words, but no issues with weight gain or constipation. I have however had an episode of GI reflux that has been challenging. Endoscopy is normal. My gyn wants me to try a low dose synthroid for my symptoms, and my pcp is more a retest some more. I am almost at the point where I need to take antidepressants. do you see this up and down with the TSH? Is this predicting that my thyroid is going to give out and I should just take the synthroid over a dose of an antidepressant. My symptoms are not terrible, just annoying and if I could feel better it would be nice!

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