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Test ID: ARBI Acetylcholine Receptor (Muscle AChR) Binding Antibody, Serum

Reporting Name

ACh Receptor (Muscle) Binding Ab

Useful For

Supporting the diagnosis of autoimmune myasthenia gravis (MG) in adults and children


Distinguishing autoimmune from congenital MG in adults and children or other acquired forms of neuromuscular junction transmission disorders


An adjunct to the test for P/Q-type calcium channel binding antibodies as a diagnostic aid for Lambert-Eaton myasthenic syndrome

Clinical Information

Fatigable weakness due to impaired postsynaptic transmission at the neuromuscular junction is characteristic of myasthenia gravis (MG). A clinical diagnosis should be supported by electrodiagnostic testing (ie, clinical-electrodiagnosis [EDX]). Positive autoimmune serology increases certainty of MG diagnosis but needs to be interpreted in the proper clinical-EDX context with response to anticholinesterase medications supporting the diagnosis. Most cases are autoimmune and are caused by IgG autoantibodies binding to critical postsynaptic membrane molecules (nicotinic muscle acetylcholine receptor [AChR] or its interacting proteins, such as muscle-specific kinase). Serologically, the detection of AChR binding antibody provides the best diagnostic sensitivity. However, the presence of both AChR binding and modulating activity improves diagnostic accuracy. Autoantibody detection frequency is lowest in patients with weakness confined to extraocular muscles (approximately 70% are positive for AChR binding antibodies) and highest in patients with generalized weakness due to MG (approximately 90% are positive for AChR binding antibodies). In adults with MG and AChR antibodies, approximately 20% will have thymoma and very rarely (<1%) extrathymic cancers. Computed tomography imaging of the chest is considered the standard of care to evaluate for thymoma.


These results should only be interpreted in the appropriate clinical and electrophysiological context and are not diagnostic in isolation.


Note: Single antibody tests may be requested in the follow-up of patients with positive results previously documented in this laboratory.


Positive results (>0.02 nmol/L) are indicative of autoimmune myasthenia gravis (MG). These results should be interpreted in the appropriate clinical and electrophysiological context.


With a diagnosis of MG, a paraneoplastic basis should be considered with thymoma being the most commonly associated tumor with MG.


The clinical sensitivity of this assay is approximately 90% in nonimmunosuppressed patients with generalized MG. The frequency of antibody detection is lower in MG patients with weakness clinically restricted to ocular muscles (71%), and antibody titers are generally low in ocular MG (eg, 0.03-1.0 nmol/L).


Negative results do not exclude the diagnosis of MG. If clinical suspicion remains and symptoms persist or worsen consider retesting. Results may be negative in the first 12 months after symptoms of MG appear or during immunosuppressant therapy. Note: In follow up of seronegative patients with adult-acquired generalized MG, 17.4% seroconvert to positive at 12 months (ie, seronegativity rate at 12 months is 8.4%). A subset of MG patients that are persistently negative for acetylcholine receptor binding antibodies will have muscle-specific kinase (MuSK) antibodies, and therefore, it is recommended to test for MuSK antibodies in seronegative patients with high clinical suspicion of MG.


In general, there is not a close correlation between antibody titer and severity of weakness, but in individual patients, clinical improvement may be accompanied by a decrease in titer.

Testing Algorithm

This is the primary diagnostic test for myasthenia gravis.


For information see:

Myasthenia Gravis Evaluation with MuSK Reflex Algorithm

Myasthenia Gravis/Lambert Eaton Syndrome Testing Algorithm

Report Available

3 to 6 days

Day(s) Performed

Monday through Sunday

Clinical Reference

1. Lennon VA. Serological profile of myasthenia gravis and distinction from the Lambert-Eaton myasthenic syndrome. Neurology. 1997;48(Suppl 5):S23-S27. doi: 10.1212/WNL.48.Suppl_5.23S

2. Lachance DH, Lennon VA. Paraneoplastic neurological autoimmunity. In: Kalman B, Brannagan III T, eds. Neuroimmunology in Clinical Practice. Blackwell Publishing Ltd; 2008:210-217

3. Gilhus NE. Myasthenia gravis. N Engl J Med. 2016;375(26):2570-2581. doi: 10.1056/NEJMra1602678

4. Nicolle MW. Myasthenia gravis and Lambert-Eaton myasthenic syndrome. Continuum (Minneap Minn). 2016;22(6, Muscle and Neuromuscular Junction Disorders):1978-2005. doi: 10.1212/CON.0000000000000415

5. Shelly S, Paul P, Bi H, et al. Improving accuracy of myasthenia gravis autoantibody testing by reflex algorithm. Neurology. 2020;95(22):e3002-e3011. doi: 10.1212/WNL.0000000000010910

Method Name

Radioimmunoassay (RIA)

Specimen Type


Ordering Guidance

For the initial diagnostic workup of patients with suspicion of myasthenia gravis, one of the following testing algorithms is recommended:

-Myasthenia Gravis Evaluation with MuSK Reflex Algorithm

-Myasthenia Gravis/Lambert Eaton Syndrome Testing Algorithm


Standalone testing ARBI / Acetylcholine Receptor (Muscle AChR) Binding Antibody, Serum is recommended in certain situations.


This test should not be requested in patients who have recently received radioisotopes, therapeutically or diagnostically, because of potential assay interference. The specific waiting period before specimen collection will depend on the isotope administered, the dose given, and the clearance rate in the individual patient. Specimens will be screened for radioactivity prior to analysis. Radioactive specimens received in the laboratory will be held for 1 week and assayed if sufficiently decayed or canceled if radioactivity remains.

Specimen Required

Patient Preparation: For optimal antibody detection, specimen collection is recommended prior to initiation of immunosuppressant medication.

Supplies: Sarstedt Aliquot Tube 5 mL (T914)

Collection Container/Tube:

Preferred: Red top

Acceptable: Serum gel

Submission Container/Tube: Plastic vial

Specimen Volume: 1.5 mL

Specimen Minimum Volume

1 mL

Specimen Stability Information

Specimen Type Temperature Time Special Container
Serum Refrigerated (preferred) 28 days
  Frozen  28 days
  Ambient  72 hours

Reference Values

≤0.02 nmol/L

Test Classification

This test was developed, and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the US Food and Drug Administration.

CPT Code Information


LOINC Code Information

Test ID Test Order Name Order LOINC Value
ARBI ACh Receptor (Muscle) Binding Ab 97558-1


Result ID Test Result Name Result LOINC Value
8338 ACh Receptor (Muscle) Binding Ab 97558-1


If not ordering electronically, complete, print, and send a Neurology Specialty Testing Client Test Request (T732) with the specimen.

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