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Acetylcholine Receptor (AChR) Antibodies, Complete Panel With Reflex to MuSK Antibodies

Acetylcholine Receptor (AChR) Binding Antibodies Complete Panel With Reflex to MuSK Antibodies
Acetylcholine Receptor (AChR) Antibodies, Complete Panel With Reflex to MuSK Antibodies
CPT: 83519(x3)
83519(x3)83519(x3)
83519(x3)83519(x3)
Updated on 06/29/2020

Synonyms

  • ACHALL
  • AG
  • MYESTTH
  • Reflex Musk

Expected Turnaround Time

2 - 5 days


Related Documents


Specimen Requirements


Specimen

Serum


Volume

4 mL divided into two tubes


Minimum Volume

2 mL (Note: This volume does not allow for repeat testing.)


Container

Red-top tube or gel-barrier tube


Collection

Allow a minimum clotting time of 30 to 60 minutes with serum separation within 2 hours of collection. Send serum samples in a plastic transport tubes.


Storage Instructions

Refrigerate


Stability Requirements

Temperature

Period

Room temperature

7 days (stability provided by manufacturer or literature reference)

Refrigerated

14 days (stability provided by manufacturer or literature reference)

Frozen

14 days (stability provided by manufacturer or literature reference)

Freeze/thaw cycles

Stable x3 (stability provided by manufacturer or literature reference)


Patient Preparation

No isotopes administered 24 hours prior to venipuncture.


Causes for Rejection

Excessive hemolysis; chylous serum; recently administered radioisotopes; plasma specimen


Test Details


Use

The IBL Acetylcholine Receptor Antibody (ACRAB) Radio Receptor Assay is for the in-vitro-diagnostic semi-quantitative determination of autoantibodies against the Acetycholine receptor in human serum and plasma. This assay is the primary test for confirming the diagnosis of acquired myasthenia gravis.


Limitations

AChR autoantibodies are not typically found in congenital myasthenia.

This panel is RUO/IUO Yes due to the following test: Acetylcholine Receptor (AChR)-blocking Antibodies [085926].

Results for this test are for research purposes only by the assay's manufacturer. The performance characteristics of this product have not been established. Results should not be used as a diagnostic procedure without confirmation of the diagnosis by another medically established diagnostic product or procedure.


Methodology

See individual tests.


Additional Information

Autoantibodies against Muscle specific Kinase: a test for Myasthenia Gravis Patients

Myasthenia Gravis (MG) with autoantibodies to Muscle specific Kinase (MuSK) is a distinct form of MG that occurs in five to eight percent of MG patients. Autoimmune myasthenia gravis is characterized by muscle weakness or inability to sustain muscle contraction, a condition first described in print in the 1600s. MG is estimated to affect between 15 and 179 per million inhabitants people worldwide, depending on location. The disease affects both women and men, and rarely children, totaling about 700,000. The most common cause of MG is autoantibodies to the complex of proteins in the muscle side of neuromuscular junction that form the acetylcholine receptor (AChR). AchR antibodies are found in about 85% of patients with myasthenic symptoms. These AChR antibodies tend to be of the IgG1 or 3 subtype and inhibit transmission of signals from the nerves to the muscles by reduction of acetylcholine receptors complexes and changes to the structure of the neuromuscular junction.

MuSK autoantibodies are found in about 40% of the AchR-negative myasthenic patients. Similarly to AChR antibodies, MuSK autoantibodies cause muscle weakness, although the typical initial complaint for MuSK autoantibodies is bulbar weakness. MuSK autoantibodies are understood to inhibit the aggregation of neuromuscular transmission complexes as MuSK, AChR and other proteins are required to orient together to form receptor complexes. However the disease associated with MuSK differs in other ways. The antibodies tend to be IgG subclass 4 antibodies, and these do not activate complement. IgG4 dimers are less stable, and dissociation causes circulating monometers as well as heterodimers. MuSK patients do not commonly have thymic disease. MuSK antibodies have an association with HLA-DQ5. MuSK antibody positive patients tend to have eye, bulbar, neck, and respiratory disturbances, which can lead to MG crises.

Laboratory Method

Antibodies specific for MuSK are measured in serum by radiommunoprecipitation (RIPA) or ELISA. This classic assay has been used in the many clinical studies of MuSK antibodies in patients. The assay developed LabCorp was shown to be specific and sensitive, and compares well to other RIPA. The assay is quantitative; binding of labeled MuSK in patient samples is compared to binding of standard antibody. This allows more precise reporting of the antibody activity in the patient sample. Patient sample antibody relative levels have been shown to relate to improvements in disease, although not to overall severity of disease. Thus precision may be an important element in assessing patient status with serial samples.

Clinical Application

Treatment of MuSK antibody positive patients diverges from treatment modalities used in AchR antibody positive patients. Thymectomy may be performed in AChR antibody positive patients with thymoma tumors or with disease that does not respond to medication. Thymectomy, in contrast, may be less effective in the treatment of MuSK antibody patients, as the operation did not reduce the antibody titers in trials, and cellular changes as seen in AcHR antibody positive patients were not seen in MuSK positive patients.

Rituxan, a chimeric anti-CD20 antibody drug has been shown to be effective in treating MuSK autoantibody positive patients. Azathioprine has been used in MuSK, AchR, or LRP4 antibody positive patients, particularly during pregnancy as the toxicity is thought to be low. Because of treatment and disease course differences diagnosis of MuSK antibody positive patients is important to the well-being of the patients.


References

Berrih-Aknin S, Le Panse R. Myasthenia gravis: A comprehensive review of immune dysregulation and etiological mechanisms. J Autoimmun. 2014 Aug;52:90-100.24389034
Conti-Fine BM, Milani M, Kaminski HJ. Myasthenia gravis: past, present, and future. Journal Clin Invest. 2006 Nov;116(11):2843-2854.17080188
Evoli A, Padua L. Diagnosis and therapy of myasthenia gravis with antibodies to muscle-specific kinase. Autoimmun Rev. 2013 Jul;12(9):931-935.23535158
Gilhus NE, Verschuuren JJ. Myasthenia gravis: subgroup classification and therapeutic strategies. Lancet Neurol. 2015 Oct;14(10):1023-1036.26376969
Koneczny I, Stevens JA, De Rosa A, et al. IgG4 autoantibodies against muscle-specific kinase undergo Fab-arm exchange in myasthenia gravis patients. J Autoimmun. 2017 Feb;77:104-115.27965060
Oger J, Frykman H. An update on laboratory diagnosis in myasthenia gravis. Clin Chim Acta. 2015 Apr 15;444:126-131.25689792
Sanders DB, Wolfe GI, Benatar M, et al. International consensus guidance for management of myasthenia gravis, Executive summary. Neurology. 2016 Jul 26;87(4):419-425.27358333
Turner JW. Myasthenia gravis: President's Address. Proc R Soc Med. 1974 Aug;67(8):763-769.4371092
Zisimopoulou P, Brenner T, Trakas N, Tzartos SJ. Serological diagnostics in myasthenia gravis based on novel assays and recently identified antigens. Autoimmun Rev. 2013 Jul;12(9):924-930.23537507

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