Test ID: ARBI
Acetylcholine Receptor (Muscle AChR) Binding Antibody, Serum
Secondary ID 
A test code used for billing and in test definitions created prior to November 2011
NY State Approved Indicates the status of NY State approval and if the test is orderable for NY State clients.
Useful For Suggests clinical disorders or settings where the test may be helpful
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 Delineates situation(s) when tests are added to the initial order. This includes reflex and additional tests.
This is the primary diagnostic test for myasthenia gravis.
See Paraneoplastic Evaluation Algorithm in Special Instructions.
Special Instructions and Forms Describes specimen collection and preparation information, test algorithms, and other information pertinent to test. Also includes pertinent information and consent forms to be used when requesting a particular test
Method Name A short description of the method used to perform the test
Radioimmunoassay (RIA)
Reporting Name A shorter/abbreviated version of the Published Name for a test; an abbreviated test name
Aliases Lists additional common names for a test, as an aid in searching
AChR (Acetylcholine Receptor)
Anti -Neuromuscular Junction Receptor Antibodies
Myasthenia Gravis Antibodies
Specimen Type Describes the specimen type needed for testing
Specimen Required Defines the optimal specimen. This field describes the type of specimen required to perform the test and the preferred volume to complete testing. The volume allows automated processing, fastest throughput and, when indicated, repeat or reflex testing.
Container/Tube:
Preferred: Red top
Acceptable: Serum gel
Specimen Volume: 2 mL
Forms: If not ordering electronically, submit a General Request Form (Supply T239) with the specimen.
Specimen Minimum Volume Defines the amount of specimen required to perform an assay once, including instrument and container dead space. Submitting the minimum specimen volume makes it impossible to repeat the test or perform confirmatory or perform reflex testing. In some situations, a minimum specimen volume may result in a QNS (quantity not sufficient) result, requiring a second specimen to be collected.
Reject Due To Identifies specimen types and conditions that may cause the specimen to be rejected
| Hemolysis | Mild OK; Gross reject |
| Lipemia | Mild OK; Gross reject |
| Icterus | Mild OK; Gross reject |
| Other | NA |
Specimen Stability Information Provides a description of the temperatures required to transport a specimen to the laboratory. Alternate acceptable temperature(s) are also included.
| Specimen Type | Temperature | Time |
|---|---|---|
| Serum | Refrigerated (preferred) | 14 days |
| Ambient | 72 hours | |
| Frozen | ||
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
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 Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
< or =0.02 nmol/L
Interpretation Provides information to assist in interpretation of the test results
Values >0.02 nmol/L are consistent with a diagnosis of acquired myasthenia gravis (MG), provided that clinical/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-aquired generalized MG, 17.4% seroconvert to positive at 12 months (ie, seronegativity rate at 12 months is 8.4%). Thirty eight percent of persistently seronegative patients have muscle-specific kinase (MuSK) antibody.
Sera of nonmyasthenic subjects bind per liter 0.02 nmol 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.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
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 co-exist. 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.
Clinical Reference Provides recommendations for further in-depth reading of a clinical nature
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 Kalman B, Brannagan T III. Blackwell Publishing Ltd, 2008, pp 210-217
Method Description Describes how the test is performed and provides a method-specific reference
Acetylcholine receptors (a mixture of adult and fetal type) are solubilized from human limb muscle in nonionic detergent and complexed with (125)I-labeled-alpha-bungarotoxin to provide antigen. After incubation with patient's serum, an excess of goat antihuman immunoglobulin G and M is added. Acetylcholine receptor-(125)I-alpha-bungarotoxin complexes to which antibodies have bound will coprecipitate with the total human immunoglobulin. The radioactivity of the washed pellet is determined. All positive results are verified by ruling out false-positive binding of immunoglobulin to (125)I-alpha-bungarotoxin, such as might occur in patients with immune complex disorders or subjects exposed to snake venom products.(Griesmann GE, Kryzer TJ, Lennon VA: Autoantibody profiles of myasthenia gravis and Lambert-Eaton myasthenic syndrome. In Manual of Clinical and Laboratory Immunology. Sixth edition. Edited by NR Rose, RG Hamilton, et al. Washington, DC, ASM Press 2002, pp 1005-1012)
Day(s) and Time(s) Test Performed Outlines the days and times the test is performed. This field reflects the day and time the sample must be in the testing laboratory to begin the testing process and includes any specimen preparation and processing time required before the test is performed. Some tests are listed as continuously performed, which means assays are performed several times during the day.
Monday through Thursday; 6 p.m., Saturday; 10 a.m.
Analytic Time Defines the amount of time it takes the laboratory to setup and perform the test. This is defined in number of days. The shortest interval of time expressed is "same day/1 day," which means the results may be available the same day that the sample is received in the testing laboratory. One day means results are available 1 day after the sample is received in the laboratory.
Maximum Laboratory Time Defines the maximum time from specimen receipt at Mayo Medical Laboratories until the release of the test result
Specimen Retention Time Outlines the length of time after testing that a specimen is kept in the laboratory before it is discarded
Performing Laboratory Location The location of the laboratory that performs the test
Test Classification Provides information regarding the medical device classification for laboratory test kits and reagents. Tests may be classified as cleared or approved by the US Food and Drug Administration (FDA) and used per manufacturer's instructions, or as products that do not undergo full FDA review and approval, and are then labeled as an Analyte Specific Reagent (ASR), Investigation Use Only (IUO) product, or a Research Use Only (RUO) product.
CPT Code Information Provides guidance in determining the appropriate Current Procedural Terminology (CPT) code(s) information for each test or profile. The listed CPT codes reflect Mayo Medical Laboratories interpretation of CPT coding requirements. It is the responsibility of each laboratory to determine correct CPT codes to use for billing.
83519
LOINC® Code Information Provides guidance in determining the Logical Observation Identifiers Names and Codes (LOINC) values for the result codes returned for this test or profile.
| Result ID | Reporting Name | LOINC Code |
|---|---|---|
| 8338 | ACh Receptor (Muscle) Binding Ab | 11034-6 |
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