Can TSH level be different based upon Labs Calculation Method?

[momofmb§rb]

Hi. My lab(a large national one used by my insurance company)gives a normal range for TSH of .4 to 5.5 MIU/L on the lab report.  I questioned them about this since their own interpretive test guide lists anything above 4.2 as either indicative of subclinical or clinical hypothyroidism, depending upon Free T4 level.  They told me that their interpretive guide needs to be updated and the 5.5 is correct.  My question is can one lab's method of analysis of TSH differ from another so that the 3.0 level for TSH that the NIH and the American Society of Endocrinology say is indicative of hypothroidism actually be equal to 5.5 based upon a different labs method of analysis?  In other words, if five different reputable labs calculated a TSH level from the same sample of blood would they all come up with the same number?  (lets say give or take 5%)  Or, is my labs upper limit of 5.5 equal to 3.0 if another lab had done the test.  My TSH was 4.2 in 5/05 (no other thyroid tests done at this time).  In 5/04 TSH was 3.3 and free T4 was .9.  My primary says there is nothing she can do because the lab is not reporting a result out of range.  I am willing to pay for anti-TPO, free t4 and tsh tests out of my own pocket, plus a visit to endocrinologist if my 4.2 level means I should be further tested for hypothyroidism.  I have complained of symptoms consistent with hypothroidism to 3 different docs over the past 2 years, but I didn't even know about hypothroid as a potential cause till I read about it in Newspaper and then checked my labs 2 months ago.

[Mark Lupo, M.D.]

The TSH above 3.0 is a suggestion by AACE and others as the upper limit of normal - labs have not universally embraced this yet so the 5.5 on one lab does NOT mean 3.0 on another.  A level above three in the presence of symptoms that may stem from hypothyroidism (please remember these symptoms have many other causes as well...) should prompt a TPO Ab check and consideration of treatment -- there is not a consensus on this, but many of us practice that way after careful discussion with the patient and consideration of other causes of symtpoms.

[tina999]

Hi,

When a lab sets up an assay to develop they find a large group of "normal" volunteers to test and "sick" volunteers.   From these huge samples they figure out what the normal and sick rnage is for any given analyte-TSH in this case.  Each lab develops thier own ref range based on these statistics thus the very small variations you will see on lab results.   For instance some labs say TSH shouldn't be over 5.0 but then others say 5.5.   It is more to do with the ranges for that specific assay which may be slightly different from another labs assay.  So one lab could measure the TSH at 4.5 and another at 4.9 on the same sample but report slightly different ranges which would account for the slightly different values.

What you are dealing with is something different.
The problem with the TSH assay is that back when they developed it they actually included a lot of people in the "normal" catagory who were in the early stages of thyroid disease, but the developers did not know that.  These folks went on to develop fullblown hypothyroidism later.  

So now the endocrinologists are all arguing over where you should treat someone.  Some say at 3.0 and some say at 5.0.   I went to my endo today and am down to 3.8 (from 200!) and he gave me the choice if I wanted to increase the dose just a bit more to get down to under 2.   It is just a matter of finding the right endo-good luck.  You could move to florida and see Dr.Mark!

I think if the labs tried to change the "normal ranges" my guess is that they'd have to retest "normal" and "sick " populations again to readjust the ranges due to the FDA issues in developing a new assay.  Not positive though.

[momofmb§rb]

Thank you for your responses.  In the past two years my total cholesterol has increased from 155 to 215.  I have had trips to the doctor for tennis elbow (I developed it from shoveling snow) that still hurts enough to wake me in the middle of the night almost 2 years later, constipation that caused a pain in my right side for 6 months, irregular periods(despite the fact that I am on the pill), and exhaustion.  My hair has thinned, lost all its shine, and is very dry.  Several of my nails are concave at this point.  Every time I go to the doctors, they take my temperature.  It is usually 97 to 97.5.  My pulse is around 60.  I am always cold.  They always comment on how low my blood pressure is. My weight has increased from about 103 to 108 over the last two years despite a better diet and more exercise (I'm 5'3").  I'd say that I have more than a few hypo symptoms, but I was resigned to the fact that it was probably due more to ageing (aging) than any thing else.  I am 43.  What really upset me was the increase in cholesterol.  That is when I pulled out all my old lab results and started looking for a cause.