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HelpTest ID MGEA Myasthenia Gravis (MG) Evaluation, Adult
Useful For
Initial evaluation of patients aged 20 or older with symptoms and signs of acquired myasthenia gravis (MG)
Bone marrow transplant recipients with suspected graft-versus-host disease, particularly if weakness has appeared
Confirming that a recently acquired neurological disorder has an autoimmune basis (eg, MG)
Providing a quantitative baseline for future comparisons in monitoring a patient's clinical course and the response to immunomodulatory treatment
Raising likelihood of neoplasia
If muscle acetylcholine receptor (AChR) modulating antibody value is (or exceeds) 90% AChR loss and striational antibody is detected, thymoma is likely. Reflexive testing will include collapsin response-mediated protein-5-lgG Western blot, ganglionic AChR antibody, glutamic acid decarboxylase (GAD65) antibody, and voltage-gated potassium channel complex (VGKC) antibody (which are frequent with thymoma).
Note: Single antibody tests may be requested in follow-up of patients with positive results documented in this laboratory.
Profile Information
| Test ID | Reporting Name | Available Separately | Always Performed |
|---|---|---|---|
| ARBI | ACh Receptor (Muscle) Binding Ab | Yes | Yes |
| ARMO | ACh Receptor (Muscle) Modulating Ab | No | Yes |
| STR | Striational (Striated Muscle) Ab, S | Yes | Yes |
Reflex Tests
| Test ID | Reporting Name | Available Separately | Always Performed |
|---|---|---|---|
| GD65S | GAD65 Ab Assay, S | Yes | No |
| CRMWS | CRMP-5-IgG Western Blot, S | No | No |
| GANG | AChR Ganglionic Neuronal Ab, S | No | No |
| VGKC | Neuronal (V-G) K+ Channel Ab, S | No | No |
Testing Algorithm
If acetylcholine receptor (AChR) modulating antibodies are ≥90% and striational antibodies are ≥1:120, then AChR ganglionic neuronal autoantibody, glutamic acid decarboxylase autoantibody, neuronal voltage-gated potassium channel autoantibody, and collapsin response-mediated response-5-IgG Western blot will be performed at an additional charge.
See Myasthenia Gravis: Adult Diagnostic Algorithm in Special Instructions.
Special Instructions
Method Name
ARBI, ARMO, GANG, GD65S, VGKC: Radioimmunoassay (RIA)
STR: Enzyme Immunoassay (EIA)
CRMWS: Western Blot
Reporting Name
MG Evaluation, AdultSpecimen Type
SerumContainer/Tube:
Preferred: Red top
Acceptable: Serum gel
Specimen Volume: 3 mL
Additional Information: Patient should have no general anesthetic or muscle-relaxant drugs in the previous 24 hours.
Forms: If not ordering electronically, complete, print, and send a Neurology Test Request Form-General (T732) with the specimen (http://www.mayomedicallaboratories.com/it-mmfiles/neurology-request-form.pdf)
Specimen Minimum Volume
2 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 an acquired disorder of neuromuscular transmission caused by the binding of pathogenic autoantibodies to muscle's postsynaptic nicotinic acetylcholine receptor (AChR). In a small minority of patients the pathogenic antibody is directed at the muscle-specific receptor tyrosine kinase (MuSK) antigen. The ensuing weakness in both cases reflects a critical loss of the AChR channel protein, which is required to activate the muscle action potential.
MG affects children (see MGEP / Myasthenia Gravis [MG] Evaluation, Pediatric) as well as adults. In adults with MG there is at least a 20% occurrence of thymoma or other neoplasm. Neoplasms are an endogenous source of the antigens driving production of autoantibodies.
Autoimmune serology is indispensable for initial evaluation and monitoring of patients with acquired disorders of neuromuscular transmission. The neurological diagnosis depends on the clinical context and electromyographic findings, and is confirmed more readily by the individual patient’s serological profile than by any single test.
Not all of the antibodies detected in this profile impair neuromuscular transmission (eg, antibodies directed at cytoplasmic epitopes accessible on solubilized AChR, or sarcomeric proteins that constitute the striational antigens).
See Myasthenia Gravis: Adult Diagnostic Algorithm in Special Instructions.
Reference Values
ACh RECEPTOR (MUSCLE) BINDING ANTIBODY
≤0.02 nmol/L
ACh RECEPTOR (MUSCLE) MODULATING ANTIBODIES
0-20% (reported as __% loss of AChR)
STRIATIONAL (STRIATED MUSCLE) ANTIBODIES
<1:120
Cautions
A positive result is not per se diagnostic of myasthenia gravis (MG). Positive values for muscle antibodies (acetylcholine receptor: AChR or striational) occur in 13% of Lambert-Eaton syndrome (LES) patients, 40% of patients with autoimmune liver disorders, approximately 10% of patients with lung cancer, and in patients with graft-versus-host disease, and recipients of D-penicillamine.
In this laboratory, false-positive results for AChR binding antibodies are excluded by retesting positive sera with (125)I-alpha-bungarotoxin in the absence of muscle AChR. False-positive results occur most frequently in the bioassay for AChR modulating antibody; serum redraw will be requested when only this assay yields a positive result. Curare-like drugs used during general anesthesia can yield transient false-positive results for AChR modulating antibodies.
Seropositive rates differ in different laboratories.
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 specimen received in the laboratory will be held 1 week and assayed if sufficiently decayed, or canceled if radioactivity remains.
Day(s) Performed
ACh receptor (muscle) binding antibody: Monday through Friday, Sunday; 2 p.m.
ACh receptor (muscle) modulating antibodies: Monday through Thursday, Saturday; 12 p.m.
Striational (striated muscle) antibodies: Monday through Friday; 2 p.m.
CRMP-5-IgG Western blot: Monday through Friday; 8 a.m.
AChR ganglionic neuronal antibody: Sunday through Thursday; 10 p.m.
Neuronal VGKC autoantibody: Sunday through Thursday; 10 p.m.
GAD65 antibody assay: Monday through Friday; 2 a.m.
Report Available
3 daysPerforming Laboratory
Mayo Medical Laboratories in Rochester
Test Classification
This test was developed and its performance characteristics determined by Laboratory Medicine and Pathology, Mayo Clinic. This test has not been cleared or approved by the U.S. Food and Drug Administration.CPT Code Information
83519-ACh receptor (muscle) binding antibody
83519-ACh receptor (muscle) modulating antibodies
83520-Striational (striated muscle) antibodies
83519-AChR ganglionic neuronal antibody (if appropriate)
83519-Neuronal VGKC autoantibody (if appropriate)
84182-CRMP-5-IgG Western blot (if appropriate)
86341-GAD65 antibody assay (if appropriate)