Test ID: ARBI Acetylcholine Receptor (Muscle AChR) Binding Antibody, Serum
Reporting Name
ACh Receptor (Muscle) Binding AbUseful For
A first-order test for the laboratory diagnosis of myasthenia gravis (MG)
Detecting "subclinical MG" in recipients of D-penicillamine, in patients with thymoma without clinical evidence of MG, and in patients with graft-versus-host disease
Distinguishing acquired disease (90% positive) from congenital disease (negative)
Monitoring disease progression in MG or response to immunotherapy
An adjunct to the test for P/Q-type calcium channel binding antibodies as a diagnostic aid for Lambert-Eaton myasthenic syndrome (LES) or primary lung carcinoma
Clinical Information
Myasthenia gravis (MG) is characterized by weakness and easy fatigability that are relieved by rest and anticholinesterase drugs. The weakness in most cases results from an autoantibody-mediated loss of functional acetylcholine receptors (AChR) in the postsynaptic membrane of skeletal muscle.
Demonstration of muscle AChR autoantibodies in a patient's serum supports the diagnosis of acquired (autoimmune) MG, and quantitation provides a baseline for future comparisons.
Muscle AChR antibodies are not found in congenital forms of MG and are uncommon in neurologic conditions other than acquired MG, with the exception of patients with paraneoplastic autoimmune neurological disorders, and Lambert-Eaton myasthenic syndrome (LES) with or without cancer (13% of LES patients have positive results for muscle AChR binding or striational antibodies). Patients with autoimmune liver disease are also frequently seropositive.
The assay for muscle AChR binding antibodies is considered a first-order test for the laboratory diagnosis of MG, and for detecting "subclinical MG" in recipients of D-penicillamine, in patients with thymoma without clinical evidence of MG, and in patients with graft-versus-host disease.
Interpretation
Values above 0.02 nmol/L are consistent with a diagnosis of acquired myasthenia gravis (MG), provided that clinical and electrophysiological criteria support that diagnosis.
The assay for muscle acetylcholine receptor (AChR) binding antibodies is positive in approximately 90% of 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).
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%). Of persistently seronegative patients, 38% have muscle-specific kinase (MuSK) antibody.
Sera of nonmyasthenic subjects bind 0.02 nmol/L or less of muscle AChR complexed with (125)I-labeled-alpha-bungarotoxin.
In general, there is not a close correlation between antibody titer and severity of weakness, but in individual patients, clinical improvement is usually accompanied by a decrease in titer.
Testing Algorithm
This is the primary diagnostic test for myasthenia gravis.
See the following algorithms in Special Instructions:
Myasthenia Gravis Evaluation with MuSK Reflex Algorithm
Myasthenia Gravis/Lambert Eaton Syndrome Diagnostic Algorithm
Myasthenia Gravis: Adult Diagnostic Algorithm
Special Instructions
Analytic Time
3 daysDay(s) and Time(s) Performed
Monday through Friday; 11 a.m., 6 p.m., 10 p.m.
Saturday; 6 a.m.
Sunday; 6 a.m., 10 a.m.
Clinical Reference
1. Lennon VA: Serological diagnosis of myasthenia gravis and distinction from the Lambert-Eaton myasthenic syndrome. Neurology 1997;48(Suppl 5):S23-S27
2. Lachance DH, Lennon VA: Chapter 19, Paraneoplastic neurological autoimmunity. In Neuroimmunology in Clinical Practice. Edited by B Kalman, T Brannagan III. Blackwell Publishing Ltd, 2008, pp 210-217
3. Gilhus NE: Myasthenia Gravis. N Engl J Med. 2016;375(26):2570-2581
4. Nicolle MW: Myasthenia Gravis and Lambert-Eaton Myasthenic Syndrome. Continuum (Minneap Minn). 2016;22(6, Muscle and Neuromuscular Junction Disorders):1978-2005
Method Name
Radioimmunoassay (RIA)
Specimen Type
SerumSpecimen Required
Patient Preparation: 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 1 week and assayed if sufficiently decayed, or canceled if radioactivity remains.
Container/Tube:
Preferred: Red top
Acceptable: Serum gel
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 U.S. Food and Drug Administration.CPT Code Information
83519
LOINC Code Information
Test ID | Test Order Name | Order LOINC Value |
---|---|---|
ARBI | ACh Receptor (Muscle) Binding Ab | 11034-6 |
Result ID | Test Result Name | Result LOINC Value |
---|---|---|
8338 | ACh Receptor (Muscle) Binding Ab | 11034-6 |
Forms
If not ordering electronically, complete, print, and send a Neurology Specialty Testing Client Test Request (T732) with the specimen.
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