Test Details
Methodology
Radioimmunoprecipitation Assay (RIPA)
Result Turnaround Time
7 - 11 days
Turnaround time is defined as the usual number of days from the date of pickup of a specimen for testing to when the result is released to the ordering provider. In some cases, additional time should be allowed for additional confirmatory or additional reflex tests. Testing schedules may vary.
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.
Serial measurement of MuSK antibodies to monitor MuSK MG treatment as MuSK antibody titer correlate with disease severity.
Limitations
Immunosuppressant therapy is a common cause of false‐seronegativity. In addition, patient’s characteristic signs of myasthenia gravis maybe obscured by a superimposed steroid‐induced myopathy.
Though a positive MuSK result is specific for the diagnosis of MuSK myasthenia gravis (MG), a negative MuSK result does not rule out a MG diagnosis.
References
Custom Additional 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 Requirements
Specimen
Serum
Volume
1 mL
Minimum Volume
0.5 mL (Note: This volume does not allow for repeat testing.)
Container
Red-top tube or gel-barrier tube
Collection Instructions
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.
Stability Requirements
| Temperature | Period |
|---|---|
| Room temperature | 14 days |
| Refrigerated | 14 days |
| Frozen | 1 year |
| Freeze/thaw cycles | Stable x6 |
Reference Range
| Musk Abs. | <1.0 U/mL | |
Result of 1.0 U/mL or higher are positive.
A positive result, in the context of congruent clinical findings, confirms the diagnosis of autoimmune muscle‐specific kinase myasthenia gravis.
Storage Instructions
Refrigerated or frozen
Causes for Rejection
Grossly hemolytic or lipemic sample will be rejected.
LOINC® Map
| Order Code | Order Code Name | Order Loinc | Result Code | Result Code Name | UofM | Result LOINC |
|---|---|---|---|---|---|---|
| 504600 | MuSK Abs, Serum | 57436-8 | 504601 | MuSK Abs, Serum | U/mL | 57436-8 |
| Order Code | 504600 | |||||
| Order Code Name | MuSK Abs, Serum | |||||
| Order Loinc | 57436-8 | |||||
| Result Code | 504601 | |||||
| Result Code Name | MuSK Abs, Serum | |||||
| UofM | U/mL | |||||
| Result LOINC | 57436-8 |