MuSK Antibodies

Test ID: 


CPT code:



  • AChR seronegative MG
  • Anti-MuSK
  • MG
  • MG antibodies

Clinical Use:

Diagnosis of muscle‐specific kinase (MuSK) myasthenia gravis.

Secondary or reflex test to aid in the diagnosis of autoimmune myasthenia gravis when first‐line tests (acetylcholine receptor antibodies) are negative.

Test Information:

Myasthenia gravis (MG) is a chronic, autoimmune disease of the motor system characterized by fatigable weakness with sensory and autonomic sparing.

MG is caused by autoantibodies against proteins of the neuromuscular junction. Most cases of generalized MG are anti-acetylcholine receptor (AChR) antibodypositive; a sub-fraction of MG patients produce antibodies against Muscle Specific receptor tyrosine Kinase (MuSK).

Of generalized MG patients who lack anti-AChR antibodies (AChR-seronegative), about 40% are positive for Muscle-Specific Kinase (MuSK) antibody.

MuSK MG accounts for 5-8% of all MG and is characterized by prominent facial, bulbar and respiratory weakness, frequent respiratory crises, and atrophy of the tongue and masseter muscles.

MuSK antibody levels have been shown to correlate with disease severity. Serial measurements may be useful to follow treatment.

Specimen Type:


Requested Volume: 

1 mL

Minimum Volume: 

0.3 mL

Container Type: 

Red-top tube or gel-barrier tube


Allow a minimum clotting time of 30 to 60 minutes with serum separation within 2 hours of collection. Send serum in a plastic transport tube. To avoid delays in turnaround time when requesting multiple tests on frozen samples, please submit separate frozen specimens for each test requested.

Storage Instructions:

Refrigerated or frozen

Stability Requirements:



Room temperature

14 days


14 days


14 days

Freeze/thaw cycles

Stable x6

Rejection Criteria:

Grossly hemolytic or lipemic sample will be rejected.

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