Muscle-Specific Kinase (MuSK) Autoantibody, Serum

MuSK Autoantibody, Muscle-Specific Receptor Tyrosine Kinase, Seronegative Myasthenia Gravis (MG), Muscle-Specific Kinase (MuSK), Antibody, IgG

Test Codes

EPIC: LAB1231962, Beaker: MUSK AB, Quest: 18842
NOTE:  The tests below must be ordered first. If the below tests are negative, testing will be sent out for MuSK.

• Acetylcholine Receptor Binding Antibody (LAB1231068)
• Acetylcholine Receptor Blocking Antibody (LAB8380)
• Acetylcholine Receptor Modulating Antibody (LAB1231688)

Department

Send Outs

Specimen Collection Criteria

Collect (preferred specimen): One Gold-top SST tube.
Also acceptable: One plain Red-top tube.

Physician Office/Draw Specimen Preparation

Let specimen clot 30-60 minutes then centrifuge to separate serum from cells. Transfer serum to plastic transport tube and maintain at refrigerate (2-8°C or 36-46) prior to transport.

Preparation for Courier Transport

Transport: 2.0 mL serum, refrigerated (2-8°C or 36-46°F). (Minimum: 0.5 mL)

Rejection Criteria

• Lipemic specimen.
• Icteric specimen.
• Hemolyzed specimens.
• Specimens not collected and processed as indicated.

In-Lab Processing

Let specimen clot 30-60 minutes then centrifuge to separate serum from cells. Transfer serum to plastic transport tube and maintain at refrigerate (2-8°C or 36-46) prior to transport.

Transport: 2.0 mL serum, refrigerated (2-8°C or 36-46°F). (Minimum: 0.5 mL)

Storage

Specimen Stability for Testing:

Room Temperature (20-26°C or 68-78.8°F): 72 hours
Refrigerated (2-8°C or 36-46°F): 42 days
Frozen (-20°C/-4°F or below): 1 year

Specimen Storage in Department Prior to Disposal:

Specimen retention time is determined by the policy of the reference laboratory. Contact the Send Outs Laboratory with any questions.

Laboratory

Sent to Quest Diagnostics, Wood Dale, IL.

Performed

Sunday – Tuesday, and Thursday.
Results available in 3-6 days.

Reference Range

Technical Result:  <1:10 Titer
Interpretation:  Negative

Test Methodology

Radioimmunassay (RIA)

Interpretation

Muscle-specific kinase (MuSK) antibody is found in a subset of patients with myasthenia gravis, primarily those seronegative for muscle acetylcholine receptor (AChR) antibody. Decreasing antibody levels may be associated with therapeutic response; therefore, clinical correlation must be strongly considered. A negative test result does not rule out a diagnosis of myasthenia gravis. 

Clinical Utility

MuSK Antibody Test – Detection of antibodies to muscle-specific receptor tyrosine kinase (MuSK) (titer test).

CPT Codes

83516

Contacts

Last Updated

11/25/2025