Acetylcholine Receptor (AChR)-binding Antibodies With Reflex to AChR-modulating Antibody

CPT: 83519
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Test Details

Synonyms

  • Acetylcholine Receptor (AChR) Profile With Reflex

Use

Diagnose myasthenia gravis (MG); monitor response to treatment of myasthenia gravis

Limitations

False positives can occur in patients with serum drawn within 48 hours of administration of general anesthesia and muscle relaxants. Antibodies to alpha-bungarotoxin may sometimes be found in patients treated with snake venom. Recently administered radioisotopes may interfere with the assay in unpredictable ways. Acetylcholine receptor autoantibodies are not typically found in congenital myasthenia gravis.

Methodology

AChR-binding assay: radioimmunoassay (RIA); reflex assay AChR-modulating antibody: cell culture based radioimmunoassay (RIA)

Additional Information

Myasthenia gravis is an autoimmune disorder manifested by muscle weakness caused by the loss or dysfunction of acetylcholine receptors (AChR) of skeletal muscle. Autoantibodies (binding, blocking, and/or modulating) to postsynaptic AChRs are detectable in the serum of 90% of patients with generalized MG and in 55% to 70% of patients with ocular myasthenia. These autoantibodies interfere with normal neuromuscular function, causing muscle weakness and fatigue. Receptor antibody levels tend to rise several weeks before symptoms increase in patients with established MG. Remission after thymectomy is associated with a progressive decline in antibody levels. Consequently, measurements of AChR antibodies can be used in monitoring disease progression as well as the effects of treatment. Modulating antibodies are responsible for the degradation of AChR at the muscle cell surface. Modulating antibodies bind to two receptor molecules on the cell surface and accelerate internalization, triggering endocytosis and degradation. The relative increase in this degradation rate closely corresponds to the disease severity.

Specimen Requirements

Specimen

Serum

Volume

1.5 mL

Minimum Volume

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

Container

Red-top tube or gel-barrier tube

Collection

Separate serum from cells within 45 minutes of collection. Send serum in plastic transport tube.

Storage Instructions

Refrigerate; stable refrigerated for 14 days. Stable at room temperature for seven days or frozen for two months.

Causes for Rejection

Improper labeling; gross microbial contamination; specimen contaminated with anticoagulants; chylous serum; plasma specimen

Clinical Information

Special Instructions

An AChR-binding antibody result <0.25 will reflex to the AChR-modulating antibody at an additional charge.

References

Griesmann GE, Kryzer TJ, Lennon VA. Autoantibody profiles of myasthenia gravis and Lambert Eaton syndrome. In: Rose NR, Hamilton RG, Detrick B, eds. Manual of Clinical Laboratory Immunology. 6th ed. Washington DC: ASM Press; 2002.
Hara H, Hayashi K, Ohta K, Itoh N, Nishitani N, Ohta M. Detection and characterization of blocking-type anti-acetylcholine receptor antibodies in sera from patients with myasthenia gravis. Clin Chem. 1993 Oct; 39(10):2053-2057. 8403390
Howard FM Jr, Lennon VA, Finley J, Matsumoto J, Elveback LR. Clinical correlations of antibodies that bind, block, or modulate human acetylcholine receptors in myasthenia gravis. Ann N Y Acad Sci. 1987; 505:526-538. 3479935
Howard JF Jr. Myasthenia gravis—A summary. Myasthenia Gravis Foundation of America, Carolinas Chapter Newsletter. November, 1997.
Lyons BW, Wu LL, Astill ME, Wu JT, Development of an assay for modulating antiacetylcholine receptor autoantibodies using human rhabdomyosarcoma cell line. J Clin Lab Anal. 1998; 12(5):315-319. 9773965
Palace J, Vincent A, Beeson D. Myasthenia gravis: Diagnostic and management dilemmas. Curr Opin Neurol. 2001 Oct; 14(5):583-589. 11562569
Wu JT, Astill M, Lloyd C, Salmon VC. Rhabdomyosarcoma cell line can be used for the isolation of soluble acetylcholine receptor for assaying blocking and modulating antibodies. J Clin Lab Anal. 1993; 7(1):11-8. 8426270

LOINC® Map

Order Code Order Code Name Order Loinc Result Code Result Code Name UofM Result LOINC
086003 Acetylchol Recep Bind Ab W/Rfx 085905 AChR Binding Abs, Serum nmol/L 11034-6
Reflex Table for AChR Binding Abs, Serum
Order Code Order Name Result Code Result Name UofM Result LOINC
Reflex 1 085935 AChR Modulating Ab 085935 AChR Modulating Ab % 30192-9

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