AChR Modulating test
 

Hello to everyone,

I had the neurologist suspect enough to run an Acetylchol Recep Bind Ab W/Rfx test. The results came back as follows:

F AChR Binding Abs, Serum <0.03 0.00-0.24 (nmol/L)
- Negative: 0.00 - 0.24
- Borderline: 0.25 - 0.40
- Positive: > 0.40
F AChR Modulating Ab >64 A 0-20 (%)
- Negative: <21
- Equivocal: 21 - 25
- Positive: >25
- The assay is linear between values of 12 and 64.
- Those <12 and >64 are reported as such. No single
- value for ACR-modulating antibody should be used as
- a sole basis for diagnosis or response to therapy.

The Doc. calls and tells me the test was positive and wanted me to redo it. This test is slightly differt which simply seems to be checking the blocking in addition to the binding & Modulating The results are as follows:

F AChR Binding Abs, Serum <0.03 0.00-0.24 (nmol/L)
- Negative: 0.00 - 0.24
- Borderline: 0.25 - 0.40
- Positive: > 0.40
F AChR Blocking Abs, Serum 16 0-25 (%)
- Negative: 0 - 25
- Borderline: 26 - 30
- Positive: >30
- .
- Results for this test are for research purposes
- only by the assay's manufacturer. The performance
- characteristics of this product have not been
- established. Results should not be used as a
- diagnostic procedure without confirmation of the
- diagnosis by another medically established
- diagnostic product or procedure.
F AChR Modulating Ab <12 0-20 (%)
- Negative: <21
- Equivocal: 21 - 25
- Positive: >25
- The assay is linear between values of 12 and 64.
- Those <12 and >64 are reported as such. No single
- value for ACR-modulating antibody should be used as
- a sole basis for diagnosis or response to therapy

So there was a broad swing in the modulating AB. Is this normal to see?
I have my good and bad days and was wondering if they caught me on a good day the second time around. I am very symptomatic for MG and was glad to finally get a name to go with my condition and was more thrilled to find there is treatment for it.

I read that false positives are rare but how rare are false negatives. Do I have MG or not? My DR. has not requested a follow up visit. Any help deciphering these test?

I found this chart and read it that positive Modulating antibodies only is a "Confirmation of diagnosis".


Test Selection Guide
Applications AChR Antibody Striational Antibody Titin Antibody
MuSK
Antibody
Binding Blocking Modulating
Initial screening x x x
Confirmation of diagnosis x xa x x xa
Monitoring therapeutic response and disease progression x x x x
Thymoma diagnosis x x
This table is provided for informational purposes only and is not intended as medical advice. A physician's test selection and interpretation, diagnosis, and patient management decisions should be based on his/her education, clinical expertise, and assessment of the patient.

AChR, acetylcholine receptor.

a When binding antibody is negative

Back to my question, can the test flucuate that much in a months time?:confused:

Should I have a third ACHr test or is there an additional test to rule MG out?

I just found this in one of the threads here in MG: "Modulating antibodies are thought to reduce acetylcholine receptors on muscle cells. They are detected in 90% of myasthenics, even when the binding antibodies are negative. But caution must always be used in making a clinical diagnosis based on a test, as the modulating antibody can be falsely positive in people who have recently taken muscle relaxants."

I do take Soma regularly, which is a muscle relaxer. My blood work was done at the same time of day. I wonder is this caused a false positive and the modulating to be >64%. I'm going to guess "Yes". urgh, back to the beginning.

Fluctuating antibodies
 

I believe all antibodies fluctuate over time. I have other autoimmune diseases and when diagnosed with them my ANA, AMA and ASMA were both very high. are now normal. The fluctuation of the Antimitochondrial Antibody made the diagnosis of Primary Biliary Cirrhosis difficult. I was finally diagnosed with PBC by liver biopsy.

When I was diagnosed with myasthenia, binding, blocking, modulating and MUSK antibodies were all negative. I strongly tested positive to a tension test and because of that the diagnosis of Myasthenia Gravis was made (EMG was borderline). My neurologist explained to me that there are most likely many more antibodies involved in myasthenia which they are unable to test for at this time.

Good luck, hope this helps

I'm sorry to hear of your DX. It sounds very complicated. It is wonderful that you have a DR. able to steer the ship on such a case

I found the type of muscle relaxer that they were referring to: suxamethonium or succinylcholine, is a nicotinic acetylcholine receptor agonist, used to induce muscle relaxation and short-term paralysis,

Soma is not any where near the same class of drug, so I am still not convinced one way or the other. I do have strong MG symptoms for several years now. My voice is beginning to weaken when physically or emotionally stressed which provided a clue towards MG.