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A Lab’s Normal Thyroid Levels May Be Abnormal for You

T4, T3, and Thyroid Stimulating Hormone (TSH) Levels Vary By Individual


Updated June 02, 2014

Nurse taking blood from patient in hospital
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In 2002, Danish researchers reported on an interesting study that looked at the monthly thyroid levels -- T4, T3, free T4 index, and thyroid stimulating hormone (TSH) -- of 16 healthy men with over a period of 12 months. What they found was that each of the individuals had different variations of their thyroid function, around unique levels - or what they referred to as "set points."

Each of the patients had his own individual thyroid function and normal level, and the researchers found that these levels tended to fluctuate slightly within their own range.

These findings led the researchers to conclude that a thyroid test result within a laboratory's reference limits - or "normal range" -- is not necessarily normal for a particular individual. In fact, the researchers also concluded that the distinction between subclinical and overt thyroid disease (abnormal serum TSH and abnormal T4 and/or T3) is actually somewhat arbitrary, because a patient's normal set point for T4 and T3 -- within the laboratory reference range -- is actually illustrative and needs to be taken into account.

These findings are consistent with other research regarding the relevance of the TSH reference range, and the understanding that the normal TSH level varies to some degree by individual.

In particular, the following is related relevant research and studies that look at subclinical thyroid levels, test results, and the controversy over the normal reference range for the TSH test:


"Narrow Individual Variations in Serum T4 and T3 in Normal Subjects: A Clue to the Understanding of Subclinical Thyroid Disease," The Journal of Clinical Endocrinology & Metabolism, Vol. 87, No. 3 1068-1072, 2002.

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