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Weak Positive Result Now False?

JoyfulGF

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JoyfulGF Apprentice
JoyfulGF
Posted

My really great Doc called me today and said that the lab which did my bloodwork contacted his office and let him know that the test was too sensitive and because my results were a very weak positive that it leads the lab to believe that my results are now actually a false positive. What in the world? I do not understand that one bit! How can a test be done like that and it be too sensitive? I changed my diet and I will testify that something is off in my body, and now it's coming into order because of this diet change. I know wheat bothers me, it's evident when I've consumed gluten. My husband knows, people around me know that I feel better, I look wayyyy better, and my body is telling me I'm better. Dr actually believes me and thinks that I shouldn't change back because of what I've told him. I'll try calling him tomorrow afternoon (he gave me his home phone if I want to call his house) and discuss it with him.

What do you think about this? Is it rather odd that tests can be a false positive and too sensitive?

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Skylark Collaborator
Skylark
Posted

Interesting. Labs sometimes re-evaluate the range they have defined as "normal", or I guess it's possible they discovered some sort of systematic error. You are super-lucky that your result was positive and it led you to go off gluten. I'm really glad to hear that you are starting to feel better. Maybe that little miracle you're hoping for will be around the corner. :)

Bubba's Mom Enthusiast
Bubba's Mom
Posted

My really great Doc called me today and said that the lab which did my bloodwork contacted his office and let him know that the test was too sensitive and because my results were a very weak positive that it leads the lab to believe that my results are now actually a false positive. What in the world? I do not understand that one bit! How can a test be done like that and it be too sensitive? I changed my diet and I will testify that something is off in my body, and now it's coming into order because of this diet change. I know wheat bothers me, it's evident when I've consumed gluten. My husband knows, people around me know that I feel better, I look wayyyy better, and my body is telling me I'm better. Dr actually believes me and thinks that I shouldn't change back because of what I've told him. I'll try calling him tomorrow afternoon (he gave me his home phone if I want to call his house) and discuss it with him.

What do you think about this? Is it rather odd that tests can be a false positive and too sensitive?

How confusing! :o If it were me..I'd stay gluten-free. You mention you've had a positive response to the gluten-free diet? Stay the course. :D

JoyfulGF Apprentice
JoyfulGF
Posted
  • Author

Interesting. Labs sometimes re-evaluate the range they have defined as "normal", or I guess it's possible they discovered some sort of systematic error. You are super-lucky that your result was positive and it led you to go off gluten. I'm really glad to hear that you are starting to feel better. Maybe that little miracle you're hoping for will be around the corner. :)

About labs re-evaluating the range....why aren't all labs the same and why don't they stick to the same every time?

I'm so glad that it was a weak positive when it was, I would be so confused...We're praying for that little one! My husband is in India right now and will be home in a week, my period was due today and she didn't show! :) :) :)

JoyfulGF Apprentice
JoyfulGF
Posted
  • Author

How confusing! :o If it were me..I'd stay gluten-free. You mention you've had a positive response to the gluten-free diet? Stay the course. :D

So confusing! I am definitely going to stay gluten-free, no doubt about it....I would be stupid not to. Thanks for the encouragement!

Skylark Collaborator
Skylark
Posted

About labs re-evaluating the range....why aren't all labs the same and why don't they stick to the same every time?

I'm not sure how to explain in lay terms. :unsure: Immunologic tests are not absolute measurements like serum sodium. The lab has to set its own ranges based on a group of normal people. (This is why TTG can be so different from lab to lab.) If the lab changes procedures, gets new suppliers for reagents, buys new instruments, or if new information becomes available about the test they will adjust the "normal" range. They must have decided that under current test conditions they were getting too many false positives.

Problem is, if they raise the "normal" range they lose sensitivity and their false negative rate goes up. You are in that group of people, where you are on the border and under the new range you would be a false negative.

I hope that makes sense? I'm having a lot of brain fog today and it's a little hard to organize my thoughts and write.

Did you and your doctor discuss getting a biopsy before you went gluten-free?

JoyfulGF Apprentice
JoyfulGF
Posted
  • Author

I'm not sure how to explain in lay terms. :unsure: Immunologic tests are not absolute measurements like serum sodium. The lab has to set its own ranges based on a group of normal people. (This is why TTG can be so different from lab to lab.) If the lab changes procedures, gets new suppliers for reagents, buys new instruments, or if new information becomes available about the test they will adjust the "normal" range. They must have decided that under current test conditions they were getting too many false positives.

Problem is, if they raise the "normal" range they lose sensitivity and their false negative rate goes up. You are in that group of people, where you are on the border and under the new range you would be a false negative.

I hope that makes sense? I'm having a lot of brain fog today and it's a little hard to organize my thoughts and write.

Did you and your doctor discuss getting a biopsy before you went gluten-free?

That does make sense, it's just a little whacked if you ask me because, like you said, they lose sensitivity and their false negative rate goes up.

I never talked to my doc about doing a biopsy...don't really want to just because it seems like this is what the problem is and I don't need a biopsy to let me know I can feel better with a gluten free diet.

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Skylark Collaborator
Skylark
Posted

That does make sense, it's just a little whacked if you ask me because, like you said, they lose sensitivity and their false negative rate goes up.

It's the really hard thing about looking at a population where everyone is slightly different. The TTG test does not necessarily read zero because antibodies cross-react. (This is handy when your immune system is trying to kill off a slightly different flu strain or bacteria it hasn't seen before.) On a test going 0-100, people with a TTG of 100 are obviously positive, people around 5 or 6 are obviously negative, but what about the middle? You might have a normal person who has an antibody from a bacterial infection that has nothing to do with celiac but it cross-reacts a little on the test and gives a TTG of 25. Then you have a celiac who is kind of low on TTG and gives a reading of 21 but it really is TTG antibody. You can't tell those people apart in the test. Set your cutoff at >20 and you will catch the celiac but biopsy the healthy person. Set your cutoff at >25 and you saved the healthy person an uncomfortable procedure but you missed the celiac.

See the problem? Labs work with this all the time, and they are constantly evaluating their "normal" ranges to make an imperfect test perform as well as possible. There is a fair amount of pressure from insurance (plus common sense) to limit unnecessary procedures though. That's part of why doctors run multiple tests. If you are borderline on one test but get positive on another it makes the diagnosis much stronger. Your doctor knows about this process, and also the added risk of false negatives with a higher threshold.

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