The TSH Reference Range Wars

I was recently approached by a person who asked me what the TSH reference range was. She had just been to her doctor complaining of many symptoms of low thyroid, with weight gain, hair loss, fatigue, muscle pains, etc. and her doctor said told her she did not need any thyroid medication because her “TSH was within the normal reference range” This is not exactly the best way to treat a patient. As you will see below, the TSH reference range is not very reliable. For some inexplicable reason, modern medicine continues to argue within itself on the proper reference range for the TSH test (Thyroid Stimulating Hormone). Here is a little history of the TSH reference range wars.

Here is a little history of the TSH reference range wars. In 2002-2003, three professional organizations revised the TSH references range lower. (10)

2002 American Association of Clinical Endocrinologists narrowed the serum TSH reference range to 0.3-3.0 mIU/L, lowering the upper reference end to 3.0.
(Baskin et al. Endocrine Practice 8:457, 2002)

2003- The National Academy of Clinical Biochemistry, Recommends a TSH upper limit of 2.5 mIU/L. (Baloch et al. Thyroid 13:42, 2003 & www nacb.org)

2003 the consensus panel (Endocrine Society, American Association of Clinical Endocrinologists, and American Thyroid Association) recommended a target TSH range of 1.0 to 1.5 mIU per liter in patients already receiving thyroxine therapy. (12)

In 2007, The endocrine Society issued new guidelines for pregnancy and preconception:

2007 Endocrine Society Pregnancy Guidelines:
Preconception & 1st trimester -keep TSH below 2.5 mIU/L
2nd and 3rd trimesters -keep TSH below 3.0 mIU/L
(Abalovich et al. JCEM 92: S1-S47, 2007)

After all the above, it was therefore a surprise to me when I came across a laboratory that for many years, actually had been using the lower TSH range (0.3 to 2.5), and then in 2010, made the decision to move back up to 0.3 to 5.0. (2) Many labs such as the one in Ontario ignored the lower recommendations and continued using the older upper range for TSH of 4.5 (3)

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