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HelpTest Code MGMR Myasthenia Gravis Evaluation with Muscle-Specific Kinase (MuSK) Reflex, Serum
Ordering Guidance
This test should not be requested for 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.
Specimen Required
Patient Preparation: For optimal antibody detection, specimen collection is recommended prior to initiation of immunosuppressant medication or intravenous immunoglobulin treatment.
Supplies: Sarstedt Aliquot Tube, 5 mL (T914)
Collection Container/Tube:
Preferred: Red top
Acceptable: Serum gel
Submission Container/Tube: Plastic vial
Specimen Volume: 3 mL
Collection Instructions: Centrifuge and aliquot serum into a plastic vial.
Forms
If not ordering electronically, complete, print, and send a Neurology Specialty Testing Client Test Request (T732) with the specimen.
Useful For
Diagnosing autoimmune myasthenia gravis (MG) in adults and children
Distinguishing autoimmune from congenital MG in adults and children or other acquired forms of neuromuscular junction transmission disorders
Establishing a quantitative baseline value that allows comparison with future levels if weakness is worsening
Profile Information
| Test ID | Reporting Name | Available Separately | Always Performed |
|---|---|---|---|
| MGMRI | MG with MuSK Interpretation, S | No | Yes |
| ARBI | ACh Receptor (Muscle) Binding Ab | Yes | Yes |
Reflex Tests
| Test ID | Reporting Name | Available Separately | Always Performed |
|---|---|---|---|
| ACMFS | AChR Modulating Flow Cytometry, S | No | No |
| MUSK | MuSK Autoantibody, S | Yes | No |
Testing Algorithm
If acetylcholine receptor (AChR)-binding antibodies are greater than 0.02 nmol/L, then AChR muscle modulating antibody will be performed at an additional charge.
If AChR-binding antibodies are 0.02 nmol/L or less, then muscle-specific kinase (MuSK) autoantibody will be performed at an additional charge.
If unable to report AChR binding antibody due to interfering substances, then AChR muscle modulating antibody will be performed at an additional charge.
If unable to report AChR binding antibody due to interfering substances and AChR muscle modulating antibody is negative, then MuSK autoantibody will be performed at an additional charge.
Method Name
ARBI, MUSK: Radioimmunoassay (RIA)
ACMFS: Flow Cytometry
MGMRI: Medical Interpretation
Reporting Name
MG Evaluation MuSK Reflex, SSpecimen Type
SerumSpecimen Minimum Volume
2 mL
Specimen Stability Information
| Specimen Type | Temperature | Time | Special Container |
|---|---|---|---|
| Serum | Refrigerated (preferred) | 28 days | |
| Frozen | 28 days | ||
| Ambient | 72 hours |
Reference Values
|
Test ID |
Reporting Name |
Methodology |
Reference Value |
|
MGMRI |
MG with MuSK Interpretation, S |
Interpretation |
NA |
|
ARBI |
ACh Receptor (Muscle) Binding Ab |
Radioimmunoassay (RIA) |
≤0.02 nmol/L |
Reflex Information:
|
Test ID |
Reporting Name |
Methodology |
Reference Value |
|
ACMFS |
AChR Modulating Flow Cytometry, S |
Flow Cytometry |
Negative |
|
MUSK |
MuSK Autoantibody, S |
RIA |
≤0.02 nmol/L |
Interpretation
Positive results in this antibody evaluation are indicative of autoimmune myasthenia gravis (MG). These results should be interpreted in the appropriate clinical and electrophysiological context.
In the presence of either acetylcholine receptor antibodies, a paraneoplastic basis should be considered with thymoma being the most frequently associated tumor with myasthenia gravis. Currently, muscle-specific kinase antibody positive MG is not associated with a paraneoplastic etiology.
Negative results do not exclude the diagnosis of an autoimmune neuromuscular junction disorder. If clinical suspicion remains and symptoms persistent or worsen, consider re-testing.
Clinical Reference
1. Li Y, Arora Y, Levin K. Myasthenia gravis: Newer therapies offer sustained improvement. Cleve Clin J Med. 2013;80(11):711-721. doi:10.3949/ccjm.80a.13044
2. Vernino S, Lennon VA. Autoantibody profiles and neurological correlations of thymoma. Clin Cancer Res. 2004;10(21):7270-7275. doi:10.1158/1078-0432.CCR-04-0735
3. Skjei KL, Lennon VA, Kuntz NL. Muscle specific kinase autoimmune myasthenia gravis in children: A case series. Neuromuscul Disord. 2013;23(11):874-882. doi:10.1016/j.nmd.2013.07.010
4. Hoch W, McConville J, Helms S, Newsom-Davis J, Melms A, Vincent A. Auto-antibodies to the receptor tyrosine kinase MuSK in patients with myasthenia gravis without acetylcholine receptor antibodies. Nat Med. 2001;7(3):365-368. doi:10.1038/85520
5. Chan KH, Lachance DH, Harper CM, Lennon VA. Frequency of seronegativity in adult-acquired generalized myasthenia gravis. Muscle Nerve. 2007;36(5):651-658. doi:10.1002/mus.20854
6. Shelly S, Paul P, Bi H, et al. Improving accuracy of myasthenia gravis autoantibody testing by reflex algorithm. Neurology. 2020 1;95(22):e3002-e3011. doi:10.1212/WNL.0000000000010910
Day(s) Performed
Profile tests: Monday through Sunday; Reflex tests: Varies
Report Available
3 to 10 daysPerforming Laboratory
Mayo Clinic Laboratories in Rochester
Test Classification
This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. It has not been cleared or approved by the US Food and Drug Administration.CPT Code Information
86041
86043 (if appropriate)
86366 (if appropriate)
LOINC Code Information
| Test ID | Test Order Name | Order LOINC Value |
|---|---|---|
| MGMR | MG Evaluation MuSK Reflex, S | 53706-8 |
| Result ID | Test Result Name | Result LOINC Value |
|---|---|---|
| 608981 | MG with MuSK Interpretation, S | 69048-7 |
| 8338 | ACh Receptor (Muscle) Binding Ab | 97558-1 |