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Reference Ranges – Why Your NORMAL Lab Results May be Misleading

Thyroid bell curve

by Mila McManus MD

So you’re convinced that you are LOW THYROID. You have classic symptoms, such as depressed moods, fatigue, weight gain, headaches, hair loss, etc, and you convince your doctor to test your thyroid level. Much to your dismay, you get a letter in the mail 2 weeks later that says your thyroid level is normal. What’s next? Your doctor offers you an antidepressant, Ibuprofen, and tells you to exercise. Does this sound familiar?

There are two problems here. First, this so- called ‘normal’ result might NOT be YOUR normal. Reference ranges for most lab values are established by testing a large number of healthy people and observing what appears to be “normal” for them. A large number of people are tested for a given lab, and in turn, a bell curve (i.e., normal distribution) is created. By statistical definitions, when one includes the results that extend 2 standard deviations beyond the average of that distribution, this encompasses 95% of the population studied. So if 95% of a sample population had thyroid levels that ranged from 5 to 500, that would be the reference range for a thyroid test. You must agree that 5 to 500 is a pretty broad range. So let’s say your thyroid level, hypothetically, is 25. That certainly does fall ‘within normal range’, but perhaps YOUR normal is 350. For another example, let’s say, hypothetically, that 5 yrs ago your thyroid level was 400. Over the past 5 years, you’ve noticed a slow, but steady decline in your energy, moods, brain function, etc, and had your thyroid checked again. This time it is 200. Both of these numbers are well within ‘normal range’, but your thyroid is now functioning 50% slower than it did 5 years ago. Because these levels are within range, your thyroid problem won’t be detected with bloodwork, and instead of addressing the underlying issues related to low thyroid function, which may or may not include thyroid hormone supplemenation, you are offered several prescription drugs to mask the symptoms that would otherwise be easily resolved.

The second problem is that doctors are taught in medical school and residency training to interpret most lab values as black and white, i.e., no gray area. This includes thyroid. According to most doctors, you do not have a thyroid problem if your lab result is ‘within normal limits’.

Test yourself for low thyroid symptoms.











By |2016-10-03T12:25:05-06:00May 13th, 2013|General|