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

Secondary ID

8338

Useful For

Confirming the diagnosis of myasthenia gravis (MG)

 

Distinguishing acquired disease (90% positive) from congenital disease (negative)

 

Detecting subclinical MG in patients with thymoma or graft-versus-host disease

 

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

Testing Algorithm

This is the primary diagnostic test for myasthenia gravis.

 

See Paraneoplastic Evaluation Algorithm in Special Instructions

Method Name

Radioimmunoassay (RIA)

Reporting Name

ACh Receptor (Muscle) Binding Ab

Specimen Type

Serum

Container/Tube:

Preferred: Red top

Acceptable: Serum gel

Specimen Volume: 2 mL

Specimen Minimum Volume

0.4 mL

Specimen Stability Information

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

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.

Reference Values

≤0.02 nmol/L

Cautions

Positive results for muscle acetylcholine receptor (AChR) binding or striational antibodies are found in 13% of patients with Lambert-Eaton myasthenic syndrome (LES). This does not mean that myasthenia gravis (MG) and LES coexist. Antibodies to P/Q type calcium channels are found in 95% of LES patients, but not in MG, except in very rare paraneoplastic cases related to small-cell lung carcinoma.

 

Positive results are frequently found with autoimmune liver disease.

 

Magnitude of the result is not useful for predicting severity of MG.

 

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.

Day(s) Performed

Monday through Friday 11 a.m., 6 p.m., and 10 p.m.; Saturday 6 a.m.; Sunday 6 a.m. and 10 a.m.

Report Available

3 days

Performing Laboratory

Mayo Medical Laboratories in Rochester

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

NY State Approved

Yes