There seems to be some confusion over what Acetylcholine Receptor Antibody test results mean. The three AChR tests are binding, blocking, and modulating. The blocking test is hardly done any more, and is seen as not necessary for diagnosis (according to the Mayo Clinic, who invented the test). The majority of MG patients test positive to the AChR binding test. However, in about 3 - 4% of patients (I've seen a higher number listed), only the modulating antibody is positive.

In the first article, it states very simply what each antibody does.

"Binding" antibodies attach to the acetylcholine receptors on nerve cells and may initiate an inflammatory reaction that destroys them.

"Blocking" antibodies may sit on the receptors, preventing acetylcholine from binding.

"Modulating" antibodies may cross-link the receptors, causing them to be taken up into the muscle cell and removed from the neuromuscular junction.

Every lab has different ranges for their tests. Some labs list an absolute number as positive, while other labs list a percentage as "negative, intermediate, or positive." Some labs use the terms unequivocal (leaving no doubt) or equivocal (ambiguous).

A false negative result can be due to being on a steroid or immunosuppressant therapy, having a low IgG level, or being in the early stages of MG. Some patients with ocular MG may test negative in the beginning of the disease.

There are, of course, other antibodies in MG, such as MuSK. More causes of MG are being found such as LRP4 and the SYT2 mutation.

If a patient has a question about a particular lab, they may want to contact that lab directly. Every lab has different classifications and guidelines. I should also add that these classifications of what is positive have changed over time, which seems contradictory to earlier findings. For example, the modulating antibody was previously shown as an absolute range of negative results, and anything greater was seen as positive. Now they are using higher ranges of that antibody as a positive result. I'm afraid that some patients might not receive a diagnosis due to this change. The best neuros take the clinical correlations into consideration when diagnosing MG, not only test results.

I hope this helps to clarify what each result means and how they are classified.

Annie

Acetylcholine Receptor (AChR) Antibody: The Test

Muscle autoantibodies in myasthenia gravis: beyond diagnosis?

ARBI - Clinical: Acetylcholine Receptor (Muscle AChR) Binding Antibody, Serum

Thank you, Annie— very helpful! The lab that did my AChR binding antibody would not explain the numbers. Plus my interest is not in my numbers alone but how they compare to those of others on this list.
Acetylcholine Receptor Binding Antibody RANGE:
Negative: < or =0.30 nmol/L
Equivocal: 0.31-0.49 nmol/L
Positive: > or =0.50 nmol/L

My number is 27.80 *Hnmol/L. That's way positive. If anyone else would like to share your numbers I would love to know.

While it's nice to know what other people's numbers are, the only ones that matter are yours! And numbers don't necessarily relate to disease severity, which is why clinical exams in MG are so important. And testing other clinical markers such as PFTs (MIP and MEP) are important (or an arterial blood gas).

I hope others will share what their numbers were, so that you can gauge how yours compare. Frankly, your numbers are quite high and that should be something your neuro is interested in!

Annie

My results were----
Blocking - 35
Modulating - 88 and.......
Binding - 1265.00

I had a transsternal thymectomy 7 weeks after my first symptom. My ptosis and blurry (not double) vision went away about 3 weeks after my surgery and 5+ years later I am still pretty much symptom free. The above test numbers were from a test done 3 years after my surgery.
I've been told repeatedly that the number values do not reflect the severity of the disease, of which I am proof of. That doesn't keep me from worrying, but I'm so thankful to have had the surgery and to have gotten the results I did. I know the mg can reappear at any time, but I also know it could stay dormant forever.

Lisa

My question is about MuSK but I don;t know if you can help Annie. I had a test years ago and was told it was negative. I had 0.02, and was 4 SD away from a result. Anything >0.6 is a result. So my question is ... could the low dose steroids I was taking at the time have affected this test ? The Neuro said "no" but somehow I can't quite believe... I have just reread the result and they mention that 3 SD is allowed ... so I basically missed a dx due to 1 Standard Deviation ?

I hate to tell a doctor that he is wrong. But he is wrong. Steroids, in a low, medium, or high dose, all affect the outward signs of MG (or other autoimmune diseases). They affect antibody tests and EMGs. There are some people on steroids who have high antibodies no matter what. There are some people who have a positive SFEMG even without symptoms!

The one thing about this stupid disease is that there is a spectrum of how it presents and how it tests. I know that doctors like their algorithms. How nice would that be if we all fit them?

I don't have the energy to put up any articles (this summer is doing a number on me). But the science of this is sound.

Are you on steroids now? If not, they should redo the MuSK—if your insurance will allow that. MuSK patients are just different than AChR ones. It is very important to know which one you have!

I had a negative AChR test and then a positive one. There are both circulating and tissue bound (those busy attacking tissues) antibodies. This has MuSK listed, even though the descriptor says drug-induced MG!

Drug-induced MG

Here you go. Look under "cautions" in this Mayo site!!!

MUSK - Clinical: Muscle-Specific Kinase (MuSK) Autoantibody, Serum

This is just an interesting description of the different AChR antibodies and how they behave.

Acetylcholine Receptor (AChR) Antibody: The Test

I hope that helps!

Annie

Thanks Annie, I am going to read these again and reread and thankyou again. I hope the summer is not too severe for you. it is really cold here and that helps me so much. I am stunned to think I should have had a result 9 years ago ?? Why did I nearly have to die on the operating table with a respiratory crisis - to get enough data to convince the "experts". I have always felt that the MuSK result was odd... Yes, I have just recently had it repeated as now my new opthamologist has said MG... and my Physician argued against the idea then did a quick eye test ... and went ...hmm... and ordered the repeated tests. I am still waiting.. Yes, I am still on low dose steroids and will be for life. Dr after Dr has told me that my dose is too low to affect MG. Too low to affect results and too low to relieve symptoms of MG. What can you do ?

How low is low?

With many drugs, it is not the amount, but the consistent dosing that helps. Why would steroids be any different? Doctors often overdose patients on Pred. Their approach is "let's nip this in the bud." Well, we all have MG forever. Higher doses of steroids don't get rid of MG, and they can cause major problems such as secondary illnesses.

Low dose naltrexone, for example, has been shown to help with other AIs. Someone I know from NZ uses that.

If doctors don't study ALL of the info there is out there, how can they know with any certainty what they are claiming? And why would they disagree with the Mayo Clinic, that clearly states steroids can cause a false negative antibody result?!

Does the low dose relieve your MG symptoms? There are objective tests that can show that, such as breathing tests.

I can't stand when logic doesn't prevail over out-dated paradigms. Even science changes over time. For example, there is a guy who can predict earthquakes with 80%+ accuracy. The experts said that no one could ever do that.

I hope your docs will maintain an open mind! And that this MuSK will be positive!

Annie

The Endos seem to think I am on too much ( low dose ) cortisone for Addisons Disease and try to get me lower but then yes - I feel much worse. So yes the low dose cortisone helps my other symptoms whatever is causing them. I have had breathing tests a few times and it is atypical asthma... ventolin no big help but cortisone is... But too much cortisone as one large dose a day makes me worse again. It has puzzled a few Drs.

It was interesting to see the Mayo reference range for MuSK is >0.2. My result in 2008 was 0.02. On cortisone. I checked and our Hospital has a reference range >0.06.

Sigh..

A low adrenal function can also make MG worse. They shouldn't mess around with adrenal function!!! Or MG.

Steroids can make MG worse, btw.

Are you on any other drugs?

Sometimes doctors need time to feel confident enough in a diagnosis. Most MG experts don't need time when it comes to MG. The diagnosis is usually very obvious!


Annie