Dear Dr. Roach: Our question has to do with the “normal ranges” for blood test results. Aren’t there standard normal ranges? We have had blood tests done at several different labs in the past few years. The last one said that the normal range for TSH is 0.35-5.50; two previous labs had different numbers.

The American Associa­tion of Clinical Endocrin­ologists says the normal range for TSH is 0.3-3.0!

Our doctor seems to have no opinion on the subject and goes with the latest lab’s “normal” range. What’s the story with lab blood test normal ranges? — R.M.G.

Answer: The difference is that some laboratories use the standard definition of 95 percent of normal controls, and that gives the range of 0.35-5.5 (I’ve seen a top-normal range of 6 from some labs).

However, the American Association of Clinical Endocrinologists has written that in a group of people carefully chosen to include only those with no evidence of thyroid disease (recognizing that minimally symptomatic hypothyroidism is not uncommon), 95 percent of the group will have TSH levels below 3.

This suggests that those with a TSH level between 3 and 5.5 may have asymptomatic or minimally symptomatic thyroid disease.

TSH levels vary during the day, and tend to increase as people get older. Not everyone with a slightly high

TSH needs treatment. Experienced clinicians combine a careful history and exam with the laboratory findings to determine when to recommend thyroid hormone replacement; there isn’t a simple number cutoff.

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