Normal Thyroid Lab Test Results May Be Abnormal for You

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

Nurse taking blood from patient in hospital
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Many patients are familiar with the concept of a "reference range" or normal range. This is the range in a test where results are considered normal or within typical boundaries. The normal or reference range is important for thyroid disease, as it is used to make a diagnosis, and to manage medication, by many practitioners.

Danish researchers reported on an interesting study that affects the way we look at the reference range.


Each month, the researchers measured T4, T3, free T4 index, and thyroid stimulating hormone (TSH) levels of a group of 16 healthy men.

What they found was that each of the individuals had different variations of their thyroid function, around unique levels. They referred to the unique level of each individual as a "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 relevant for a particular individual.

In fact, the researchers also concluded that the distinction between subclinical and overt thyroid disease (which is defined as abnormal TSH along with abnormal T4 and/or T3) is actually rather arbitrary.

A patient's normal set point for T4 and T3 -- within the laboratory reference range -- is actually more illustrative and needs to be taken into account in making a diagnosis, and in managing treated hypothyroidism.

What Does This Mean for Thyroid Patients

This was a small study, so we can't draw major conclusions.

But it does underscore an understanding that some doctors and patients have about thyroid diagnosis and treatment. Mainly, the thyroid tests, and where you fall in the reference range, is only one factor among many in optimal diagnosis and management of thyroid conditions.

Where Can You Learn More?

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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