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Change in free T4 reference range!
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Change in free T4 reference range!

My lab decided to change the free T4 reference from 10 - 20 pmol/L to 15 - 30 pmol/L. What the!? So now my free T4 is "normal" during a hyperthyroid flare up. *rolls eyes*

--- TSH: <0.05 mU/L (0.20 - 4.00)
Free T4:  25 pmol/L (15 - 30)
++ Free T3:  8.0 pmol/L (2.8 - 6.8)
Anti-Thyroglobulin Ab: <10 U/mL (<60)
+++ Anti-Thyroid Peroxidase Ab: 1900 U/mL (<60)
9 Comments Post a Comment
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Avatar_f_tn
We've been seeing some strange ranges here as well.  While a "typical" FT4 range is somewhere around 0.8-1.8, I've recently seen one that topped out at 6 and another that topped out at 12 (TWELVE!).  Both were verified by the posters.

I can only assume that too many hypers were having to be treated???!!!  Okay, I'll pry my tongue out of my cheek now...
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Avatar_m_tn
The only thing I can think of is that reference ranges are calculated by the lab based on all the testing they do, so hypo and hyper patients are included in the data.  Then they usually make the assumption that about 2.5% of patients are hypo and similar for hyper, and draw the range limits accordingly, at plus and minus two standard deviations from the average.  

Seems like that I recall something posted here recently about the reagent used in testing was resulting in higher Free T4 results, so maybe they are adjusting ranges for that reason.  If that is the case, then when Red is tested, her Free T4 might run higher than previously, but that certainly doesn't seem to account for the huge increase in the upper range limit.  I think I would ask how the need for a change was determined.
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Avatar_f_tn
If hypo and hyper patients were both included in the data, wouldn't the bottom of the range lower at the same time as the top was rising?

The higher results due to the reagent were, I believe, 9% higher.  Red's range went up by 50% on both ends.  I'm kind of at a loss on how to deal with this.  It just doesn't seem reasonable to calculate where someone is in a range when the upper limit Is 12 compared to the usual approximately 1.8.  

"I think I would ask how the need for a change was determined."  That's why we have you!  We are asking!  LOL    
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Avatar_m_tn
"If hypo and hyper patients were both included in the data, wouldn't the bottom of the range lower at the same time as the top was rising?"

I was just explaining my understanding of how ranges are established, and why they are so erroneous.  If the new reagent caused 9% higher results, then you could expect the entire population of recent test data and ranges to be about 9% higher.  But, what if they just incorporated all the new (higher) results in the old  data base?  The combined data would result in a greater standard deviation and thus a much wider reference range.  

Further questions would be whether only the new reagent is being used by a given lab.  Or do they still use some of the old reagent that might be left over?  If using both, that would further exacerbate  (I have been looking for a place to use that word for years) the variability in results and accordingly the reference range.  

I really can't understand how a reagent supplier can get away with something like that anyway.
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Avatar_m_tn
And I think Red is just the person to beat up on her doctor and lab and make them 'fess up, on the reason behind the enormous change, and whether it is even reasonable.  
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1756321_tn?1377771734
There is no mention of reagent changes on pathology notes. I think that may be just for US labs?  Maybe there is a shortage of anti-thyroid meds. LOL
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649848_tn?1357751184
My latest lab sheet has the following notation:  "The current lot of free T4 reagent available from the manufacturer produces results that are approximately 9% higher than previous reagent lots.  Please interpret these results accordingly."

The range is the same it's always been: 0.8-1.8.  
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Avatar_m_tn
It is interesting that they tell you to interpret them accordingly and then don't tell you how to do that!

Nice!

I think it is a conspiracy by Dr's to tell you how unreliable and useless the FT4 number is and that is why they must go back to the trusty TSH as it is so awesome to use! - just kidding

Sure blows a person who is trying to really document and track lab values against dosages and symptoms.  Throws it for a loop.

I'm really starting to think this should go full circle back to the beginning.  In the beginning a person was treated on symptoms and was given thyroid in increments until the symptoms went away.  NO lab testing at all.  I think if we went back to this a WHOLE lot of people will be treated and feeling MUCH, MUCH better.
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1756321_tn?1377771734
Okay, it looks like reagent changes aren't a factor in lab ranges. I go by symptoms but my endo requested these labs prior to starting Armour. I asked for a TSI antibody test as well and TPOAb and TgAb were tested instead. I believe this is the third time i've asked for a TSI antibody test and another test shows up instead. Pfft!  There seems to be some sort of conspiracy going on with QML pathology. They probably changed a few reference ranges for a laugh too. :)
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