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Understanding Thyroid Lab Tests

The Free T3 (FT3) Test

By Ken Woliner, M.D., A.B.F.P.

Updated May 16, 2014

So what is normal? When specimens are sent to Quest, normal is 230-420 pg/dL. If you are lower than 230 or above 420, you are “abnormal". That doesn’t tell the whole story, however. There is a difference between “normal" and “optimal". Someone can be “low normal" with a Free T3 of 231 and still feel crummy.

Some of my patients, have many hypothyroid symptoms, but have normal lab tests. When they have “low normal" values, I often will empirically try thyroid medication by starting low and going slow. If my patients feel better with medication, I interpret this situation as one where the laboratory tests do not tell the whole story, and that in the future I would make medication adjustments based upon their symptoms and physical exam. If they feel worse with less thyroid medication (such as gaining weight, being more fatigued), I give them more. If they feel like they are getting too much thyroid medication (heart palpitations, anxiety), I give them less. As an aside – giving thyroid hormone to patients who are not truly hypothyroid does not cause these patients to lose weight. They wind up only getting the side effects (such as palpitations), but no benefits (there will be no weight loss if thyroid is not the true problem).

It is important to realize that if a patient has thyroid antibodies, all bets are off. All thyroid blood tests from that point on are thrown off, including the Free T3. In that case, one definitely has to go by symptoms to decide the correct level of thyroid medication. Please see my article Understanding Thyroid Lab Tests for a more complete description of why laboratory tests can be thrown off by these antibodies.


Dr. Kenneth Woliner is a board-certified family physician in private practice in Boca Raton. Though he often recommends vitamin supplements, he does not sell them due to conflict of interest concerns. He can be reached at Holistic Family Medicine, 2499 Glades Road #106A, Boca Raton, FL 33431; 561-620-7779. E-mail: knw6@cornell.edu

Reprinted with permission. Article originally published online.

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