Ordering Recommendation

Secondary test for the diagnosis of generalized or ocular myasthenia gravis in patients with no detectable acetylcholine receptor (AChR) antibodies.

New York DOH Approval Status

This test is New York state approved.

Specimen Required

Patient Preparation

One 4 mL plain red or serum separator tube (SST)

Specimen Preparation

Separate from cells ASAP or within 2 hours of collection.  Transfer 2 mL of serum to an ARUP standard transport tube. (Min: 0.5 mL)

Storage/Transport Temperature


Unacceptable Conditions

Grossly lipemic, icteric, or hemolyzed specimens.


After separation from cells: Ambient: 48 hours; Refrigerated: 2 weeks; Frozen: 1 month (avoid multiple freeze/thaw cycles)


Semi-Quantitative Cell-Based Indirect Fluorescent Antibody


Mon, Wed, Fri


1-6 days

Reference Interval

Test Number
Reference Interval
  MuSK Ab IgG CBA IFA Screen, Serum Less than 1:10

Interpretive Data

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.

This indirect fluorescent antibody cell-based assay (CBA) utilizes muscle-specific kinase (MuSK) transfected cells for the detection of the MuSK IgG antibody.

Compliance Category

Laboratory Developed Test (LDT)


If MuSK SER antibody IgG is positive, then titer will be added. Additional charges apply.

Hotline History


CPT Codes

86366; if reflexed, add 86256


Component Test Code* Component Chart Name LOINC
3006252 MuSK Ab IgG CBA IFA Screen, Serum 38362-0
* Component test codes cannot be used to order tests. The information provided here is not sufficient for interface builds; for a complete test mix, please click the sidebar link to access the Interface Map.


  • Muscle-Specific Kinase
  • Muscle-Specific Kinase Antibody by CBA
  • Muscle-Specific Receptor Tyrosine Kinase
  • MuSK
  • MuSK Autoantibody
  • Myasthenia Gravis
  • Seronegative Myasthenia Gravis
Muscle-Specific Kinase (MuSK) Antibody, IgG by CBA-IFA with Reflex to Titer, Serum