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:
- What is the Optimal TSH Level for Thyroid Patients?
- What is a Normal TSH?
- What Is a Normal Thyroid Stimulating Hormone - TSH - Level
- Does Your Doctor Know About the New TSH Lab Standards?
- Endocrinologists Say TSH Normal Range is Now 0.3 to 3
- The TSH Reference Range Wars
"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.