Avatar universal

Those ranges....and their meaning....

So I had labs done yesterday morning......the ft3 range has been (.60-1.20) forever...

Today the range is (.65-1.44) @same hospital..

I questioned them about it and they said they had updated their ranges...

What I'm trying to figure out is if the numbers are the same no matter the range, if This were the case why would y'all always ask for ranges...

So if my ft3 is 1.33 (.65-1.44)  what would it be if the range was (.60-1.20) ?is there a way to know?

Part of me seems to think 1.33 nanograms per declitre should be the same no matter the range used....
What am I missing?

4 Responses
Sort by: Helpful Oldest Newest
Avatar universal
Lab testing for FT4 and FT3 is not standardized like it is for TSH.  Each lab can have different test equipment and standards they use to calibrate.   So each lab could get different test results from the same patient.  So a test result has to be compared to reference ranges from the same lab report.  

In addition,  to establish reference ranges the labs will do a statistical analysis of a database of test results and establish the average and  upper and lower limits that include 95% of all results.  Since the lab has no idea of a patient's thyroid status, the database excludes only those with TSH above range.  Thus the database can include patients who have central hypothyroidism (with relatively low TSH and FT4 and FT3 levels) as well as patients who are already on thyroid med.   So the calculated reference ranges are far too broad and skewed to the low end.  

It is important to note that hypothyroidism is best defined as "insufficient T3 effect in tissue throughout the body due to inadequate supply of, or response to, thyroid hormone".    There is no reliable biochemical test for tissue thyroid status.    TSH has only a negligible correlation with tissue thyroid status.  FT4 and FT3 have only a weak correlation  with tissue thyroid status.    The very best way to diagnose and treat a hypothyroid patient is  with a full medical history, along with an evaluation for symptoms that occur more frequently with hypothyroidism,  and expanded testing.    Tests should always include Free T4 and Free T3, initially Reverse T3, cortisol, Vitamin D, B12 and ferritin.  

So my question to you is, what symptoms, if any, do you have?   This link has a good lit of typical hypo symptoms that might be useful as a reference.    Also one thing to note is that you should not assume any symptom is just age related and not identify it as a possible symptom of hypothyroidism.  

Helpful - 0
Avatar universal
Well yes it was ft4, good job catching my messed up detail.thank you.
So what I guess I'm not comprehending is. Would it be correct if I had the same lab with the same number done yesterday at the old range it would be high but today it is low enough...
Why do we care what lab ranges are if a nanogram is a nanogram.... So if I did go to your lab would my number of 133nanograms per declitre be somehow measured differently? Or is it a regional thing?where you live people need higher levels or what?
Thanks again.
Helpful - 0
Avatar universal
I have never seen a range like that for Free T3.  Could it be Free T4 instead?
Helpful - 0
649848 tn?1534633700
It's not unusual for labs to change ranges now and then if they change equipment, reagents or other factors in the testing process.  

The idea of giving us your ranges each time you post lab results is so we can see where your results fall within the particular ranges your lab uses.  Since your lab has changed the ranges, you can see how results falls differently in the range.   With the current range your FT3 is at 86% of the range, which is plenty high, but not outrageous; many people do fine with it there (I do).  At the old range, your FT3 was above range, indicating you were over medicated.  Just imagine if we compared your result to the range my lab uses, which is 2.3 - 4.2... your result would actually be way under range and we'd assume you need to increase your dosage considerably.
Helpful - 0
Have an Answer?

You are reading content posted in the Thyroid Disorders Community

Top Thyroid Answerers
649848 tn?1534633700
Avatar universal
1756321 tn?1547095325
Queensland, Australia
Learn About Top Answerers
Didn't find the answer you were looking for?
Ask a question
Popular Resources
We tapped the CDC for information on what you need to know about radiation exposure
Endocrinologist Mark Lupo, MD, answers 10 questions about thyroid disorders and how to treat them
Herpes sores blister, then burst, scab and heal.
Herpes spreads by oral, vaginal and anal sex.
STIs are the most common cause of genital sores.
Condoms are the most effective way to prevent HIV and STDs.