Thyroid Blood Tests and Their Role in Diagnosis

August 4, 2011

If you or your doctor suspect you have a thyroid problem, the first step in diagnosis for many practitioners is to perform a blood test. The test usually done to evaluate thyroid function is the Thyroid Stimulating Hormone — or TSH test.

Actually, many practitioners seem to think that diagnosing a thyroid problem is as simple as having blood drawn, sending it to a lab, and then seeing whether the results are flagged by the lab as abnormal.

Unfortunately, this method fails patients on a number of levels.

First, even if you agree — and some physicians don’t — that the TSH is all that is needed to diagnose a thyroid condition, the medical community can not even agree over what the “normal range” should be for the TSH test.

Until late 2002, the reference range for the TSH test was approximately 0.5 to 5.0. TSH levels below .5 were considered hyperthyroid (overactive), and levels above 5.0 were considered hypothyroid (underactive.) Then, the American Association of Clinical Endocrinologists and National Academy of Clinical Biochemistry recommended a narrowing of the range, to take into account that people in the upper end of the range were actually evidencing early, but active, thyroid disease. Their guidelines recommended that doctors and laboratories follow a new range of 0.3 to 3.0. Surprisingly, almost four years later, some doctors and many labs are still using the old range, and some practitioners are practicing according to the new range. So the same TSH level — 4.0 for example — could be diagnosed as hypothyroid by one practitioner, and normal by another.

AACE has estimated that the new guidelines would double the number of people who have abnormal thyroid function, bringing the total to as many as 27 million, up from 13 million under the old guidelines. And actually, some experts are now saying that the new guidelines would mean that as many as 59 million Americans have a thyroid dysfunction. So, the fact that there is disagreement on these most fundamental testing guidelines represents a serious oversight for many millions of undiagnosed — and ultimately misdiagnosed — thyroid patients.

Second, reliance on the TSH test overlooks the research that has shown that testing for the presence of thyroid antibodies may help detect thyroid disease in its early stages. And, if Hashimoto’s antibodies are detected, for example — a sign that the immune system has turned on the thyroid — but TSH has not yet elevated, treatment with thyroid hormone can actually prevent progression to overt hypothyroidism.

Third, and perhaps most important, reliance on the TSH test as the sole means of diagnosis fails to take into account the importance of a clinical examination, as well as family and personal history. To diagnose thyroid disease, a practitioner should palpate the thyroid, feeling for enlargement, nodules or lumps. Your face should be examined for evidence of puffiness or swelling, and loss of eyebrow hair. Your blood pressure, pulse, and any weight changes should be evaluated. Your hair should be examined for thinning. Reflexes should be tested. Your eyes should be looked at for signs of thyroid eye disease. Skin should be examined for extreme dryness, hives, pretibial myxedema, and other potential signs of a thyroid condition. Having any past personal history, or family history of thyroid problems, also raises the index of suspicion for a thyroid problem dramatically. The current method, in which clinical observations and history are trumped by blood test results, does a tremendous disservice to patients, and in reality, makes doctors unnecessary, as “diagnosis” becomes solely a matter of reading a blood test result.

Blood tests for TSH can be a part of thyroid diagnosis. But the TSH test should never be the only factor in making a diagnosis.

Your practitioner should perform a hands-on physical examination, and if you have hypothyroidism symptoms or a personal or family history, a thorough practitioner will often perform thyroid antibodies tests in addition to TSH tests.

Ultimately, some practitioners believe that even in the absence of abnormal TSH (by even the new narrower guidelines), symptomatic evidence of hypothyroidism should be treated with a low therapeutic dose of thyroid hormone replacement, to evaluate response. In this situation, a practitioner is attempting to determine if symptoms will resolve without any adverse effects from the medication (such as high heart rate, or elevated blood pressure).

Ultimately, the most important message for patients: do not accept “your thyroid test was normal” as an appropriate response from your practitioner, because, as you can see, it doesn’t mean you don’t have a thyroid condition. Be sure to ask the right questions, and insist on the right type of tests and examination, to ensure that you are getting the best possible care.

(June 2006)

Mary Shomon is an internationally-known thyroid patient advocate, and is author of a number of best-selling health books, including Living Well With Hypothyroidism and The Thyroid Diet. Since 1997, she has run the Internet’s most popular thyroid patient sites: About.com Thyroid Site  and Thyroid-Info.com

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Tags: blood test, thyroid blood tests

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