Test ID: MGEA
Myasthenia Gravis (MG) Evaluation, Adult
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
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 AChR modulating antibody value is (or exceeds) 90% acetylcholine receptor (AChR) loss and striational antibody is detected, thymoma is likely. Reflexive testing will include CRMP-5-lgG Western blot, ganglionic AChR antibody, GAD65 antibody, and 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 A profile is a group of laboratory tests that are ordered and performed together under a single Mayo Test ID. Profile information lists the test performed, inclusive of the test fee, when a profile is ordered and includes reporting names and individual availability.
| 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 Lists test(s) that may or may not be performed, at an additional charge, depending on the result and interpretation of the initial test(s)
| 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 Delineates situation(s) when tests are added to the initial order. This includes reflex and additional tests.
If AChR modulating antibodies are > or =90% and striational antibodies are > or =1:60, AChR ganglionic neuronal autoantibody, glutamic acid decarboxylase autoantibody, neuronal voltage-gated potassium channel (VGKC) autoantibody, and CRMP-5-IgG Western blot will be performed at an additional charge.
See Myasthenia Gravis: Adult Diagnostic 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
ARBI/8338, ARMO/83378, GANG/84321, GD65S/81596, VGKC/89165: Radioimmunoassay (RIA)
STR/8746: Enzyme Immunoassay (EIA)
CRMWS/83107: Western Blot
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-Skeletal Muscle Antibodies
GAD65 (Glutamic Acid Decarboxylase)
Muscle End-Plate Antibodies
Myasthenia Gravis Antibodies
Myoid Antibody
Neuronal Potassium Channel Ab
Striational (Striated Muscle) Antibodies
VGKC
VGPC
Voltage-Gated Potassium Channel Ab
Potassium Channel Antibodies (specify)
Glutamate Decarboxylase Antibodies (GAD65)
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: 3 mL
Additional Information: Patient should have no general anesthetic or muscle-relaxant drugs in the previous 24 hours.
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 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/83371 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 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.
ACh RECEPTOR (MUSCLE) BINDING ANTIBODY
< or =0.02 nmol/L
ACh RECEPTOR (MUSCLE) MODULATING ANTIBODIES
0-20% (reported as __% loss of AChR)
STRIATIONAL (STRIATED MUSCLE) ANTIBODIES
<1:60
Interpretation Provides information to assist in interpretation of the test results
The patient's autoantibody profile is more informative than the result of any single test for supporting a diagnosis of myasthenia gravis (MG), and for predicting the likelihood of thymoma (see MGETH/83372 Myasthenia Gravis [MG] Evaluation, Thymoma).
Muscle acetylcholine receptor (AChR) and striational autoantibodies are characteristic but not diagnostic of MG. One or both are found in 13% of patients with Lambert-Eaton Syndrome (LES), but P/Q-type calcium channel autoantibodies are very rare in MG.
Results are sometimes positive in patients with neoplasia without evidence of neurological impairment.
Titers are generally higher in patients with severe weakness, or with thymoma, but severity cannot be predicted by antibody titer.
Test results for muscle acetylcholine receptor and striational antibodies may be negative for 6 to 12 months after MG symptom onset. Only 8% of nonimmunosuppressed patients with generalized MG remain seronegative beyond 12 months for all autoantibodies in the adult MG evaluation. Of those patients 38% will have the alternative muscle-specific receptor tyrosine kinase (MuSK)-specific autoantibody.
MuSK antibody-positive patients lack thymoma, and have predominantly oculobulbar symptoms that respond to plasmapheresis and immunosuppressant therapy. They do not benefit from thymectomy.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
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.
Clinical Reference Provides recommendations for further in-depth reading of a clinical nature
1. Lennon VA: Serological profile of myasthenia gravis and distinction from the Lambert-Eaton myasthenic syndrome. Neurology 1997;48(Suppl 5):S23-S27
2. Harper CM, Lennon VA: Lambert-Eaton syndrome. In Current Clinical Neurology: Myasthenia Gravis and Related Disorders. Edited by HJ Kaminski. Totowa, NJ, Humana Press, 2002, pp 269-291
3. Hoch W, McConville J, Helms S, et al: Auto-antibodies to the receptor tyrosine kinase MuSK in patients with myasthenia gravis without acetylcholine receptor antibodies. Nat Med 2001 Mar;7(3):365-368
4. Chan K-H, Lachance DH, Harper CM, Lennon VA: Frequency of seronegativity in adult-acquired generalized myasthenia gravis. Muscle Nerve 2007;36:651-658
5. Skjei KL, Lennon VA, Kuntz NL: Muscle specific kinase antibody-associated myasthenia gravis in children; clinical, serologic, electrophysiologic and pathologic characteristics and response to treatment. Annual Neurol 62(S11):S145-S146
Method Description Describes how the test is performed and provides a method-specific reference
Muscle acetylcholine receptor (AChR) binding (IgG and IgM) are measured quantitatively by immunoprecipitation assays. The high-affinity ligand (125)I-alpha-bungarotoxin is complexed with detergent-solubilized muscle AChR prepared from a mixture of innervated and denervated human muscle. AChR modulating antibody is detected in a bioassay; (125)I-bungarotoxin measures percent loss of AChR from viable, noninnervated, monolayer cultures of human muscle cells following 14-hour incubation with patient's serum. The EIA used to detect striational antibodies (IgG, IgM, and IgA) employs as antigen a mixture of sarcomeric proteins extracted from healthy adult rat skeletal muscle.(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, B Detrick. 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.
ACh receptor (muscle) binding antibody: Monday through Thursday; 6 p.m., Saturday; 10 a.m.
ACh receptor (muscle) modulating antibodies: Monday through Thursday; 11 a.m.
Striational (striated muscle) antibodies: Monday through Thursday, Sunday; 10:30 p.m.
CRMP-5-IgG Western blot: Monday through Friday; 6 a.m.
AChR ganglionic neuronal antibody: Tuesday, Thursday, Sunday; 6 a.m
Neuronal VGKC autoantibody: Tuesday, Thursday, Sunday; 6 a.m.
GAD65 antibody assay: Monday through Thursday, Sunday; 8 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.
83519-59-ACh receptor (muscle) binding antibody
83519-59-ACh receptor (muscle) modulating antibodies
83520-Striational (striated muscle) antibodies
83519-59-AChR ganglionic neuronal antibody (if appropriate)
83519-59-Neuronal VGKC autoantibody (if appropriate)
84182-CRMP-5-IgG Western blot (if appropriate)
86341-GAD65 antibody assay (if appropriate)
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 |
| 8879 | ACh Receptor (Muscle) Modulating Ab | 30192-9 |
| 8746 | Striational (Striated Muscle) Ab, S | 8097-8 |
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