Serum

Patient should have no general anesthetic or muscle-relaxant drugs in the previous 24 hours.

For optimal antibody detection, specimen collection is recommended prior to initiation of immunosuppressant medication.

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.

Testing Algorithm:
If acetylcholine receptor (AChR) modulating antibodies are > or =90% and striational antibodies are > or =1:120, then AChR ganglionic neuronal autoantibody, glutamic acid decarboxylase autoantibody, neuronal voltage-gated potassium channel autoantibody, and CRMP-5-IgG Western blot will be performed at an additional charge.

Preferred Minimum: 3 mL serum
Absolute Minimum: 2 mL serum

Monday through Sunday

3 days upon receipt at reference laboratory

MG with MuSK Interpretation, S: NA
ACh Receptor (Muscle) Binding Ab: < or =0.02 nmol/L
AChR Modulating Flow Cytometry, S: Negative
MuSK Autoantibody, S: < or =0.02 nmol/L

This mailout test requires Neurology attending approval. Mailouts staff will not process order without approval. If approval is given, the name of the Neurology attending can be selected in the drop-down menu to the right of the approval warning in Epic when ordering the test.

Depending on results of initial testing, the reference laboratory performing this mailout test can initiate further reflex testing that will involve additional charges for the patient.

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, and VGKC antibody (which are frequent with thymoma).

Useful For:
Diagnosis for 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.

MG with MuSK Interpretation, S: Interpretation
ACh Receptor (Muscle) Binding Ab: Radioimmunoassay (RIA)
AChR Modulating Flow Cytometry, S: Flow Cytometry
MuSK Autoantibody, S: RIA

83519, 86255 (if appropriate)