LabCorp and its Specialty Testing Group, a fully integrated portfolio of specialty and esoteric testing laboratories.
To help diagnose myasthenia gravis (MG) and to distinguish between MG and other conditions with similar symptoms
When you have symptoms that suggest MG, such as a drooping eyelid, double vision, difficulty chewing or swallowing, and/or weakness in specific muscles
A blood sample drawn from a vein in your arm
Acetylcholine receptor (AChR) antibodies are autoantibodies produced by the immune system that mistakenly target proteins called acetylcholine receptors that are located on skeletal muscle fibers. This test detects and measures AChR antibodies in the blood.
Acetylcholine receptors function as "docking stations" for acetylcholine, a chemical substance (neurotransmitter) that transmits messages between nerve cells. Muscle movement starts when an impulse is sent down a nerve to the nerve ending, where it stimulates the release of acetylcholine. Acetylcholine travels across a microscopic gap between the nerve ending and a muscle fiber at the "neuromuscular junction." When it reaches the muscle fiber, it binds to one of many acetylcholine receptors and activates it, initiating muscle contraction.
AChR antibodies impede communication between nerves and skeletal muscles, inhibit muscle contraction, and cause rapid muscle fatigue by preventing activation of the acetylcholine receptors. They do this in three major ways:
The end result of this interference is the development of myasthenia gravis (MG), a chronic autoimmune disorder associated with the presence of these antibodies and with their effects on muscle control.
AChR antibodies may be detected in different ways to determine which mechanism may be the problem in a particular individual, and the antibodies may be referred to as "binding," "blocking," or "modulating." However, the technique that measures "binding" is the most commonly performed and, generally speaking, it is rare for the other two tests to be positive without the "binding" test being positive as well. These other approaches may be useful when a healthcare practitioner strongly suspects myasthenia gravis and the "binding" test is negative.
An acetylcholine receptor (AChR) antibody test is used to help diagnose myasthenia gravis (MG) and to distinguish it from other conditions that may cause similar symptoms, such as chronic muscle fatigue and weakness.
AChR antibodies hinder the action of acetylcholine, a chemical (neurotransmitter) that transmits messages between nerve cells. The antibodies do this in three major ways:
Three different types of tests are available to determine which of these may be the problem in a particular individual. However, the test that measures "binding" antibodies is most commonly used because it is generally rare for the other two tests to be positive without the "binding" test being positive as well. These other tests may be used when a healthcare practitioner strongly suspects myasthenia gravis and the "binding" test is negative.
One or more of the AChR antibody tests may be ordered as part of a panel of tests that may also include a striated muscle antibody test to help establish a diagnosis. Depending upon results, an anti-MuSK (muscle-specific kinase) antibody test may also be ordered.
People with MG often have an enlarged thymus gland and may have thymomas (typically benign tumors of the thymus). Located under the breastbone, the thymus is an active part of the immune system during childhood but normally becomes less active after puberty. If a thymoma is detected, such as during a chest computed tomography (CT) scan done for a different reason, then an AChR antibody test may sometimes be used to determine whether the person has developed these antibodies.
The AChR antibody test may be ordered when a person has symptoms that suggest myasthenia gravis, such as:
An AChR antibody test may sometimes be ordered when a thymoma is detected during an imaging scan.
AChR antibodies are not normally present in the blood. They are autoantibodies and their presence indicates an autoimmune response.
If a person has AChR antibodies and symptoms of myasthenia gravis (MG), then it is likely that the person has this condition.
AChR antibodies may also be positive with some thymomas, in people who are being treated with drugs such as penicillamine, with some small cell lung cancers, with autoimmune liver disease, and with Lambert-Eaton myasthenic syndrome (a condition associated with interference with the release of acetylcholine from the nerve ending).
A negative test result does not rule out MG. Up to 50% of those with ocular MG (affecting only eye-related muscles) and about 10-15% of those with generalized MG will be negative for AChR antibodies. Results from other tests for autoantibodies, such as anti-MuSK (muscle-specific kinase) antibody test and anti-striated muscle antibody test, may aid in establishing a diagnosis. Up to 70% of people suspected to have generalized MG but who are negative for AChR antibodies will be positive for anti-MuSK antibodies.
Use of drugs such as succinylcholine can increase AChR antibodies.
People who have MG are more likely to also have other autoimmune disorders, such as rheumatoid arthritis or lupus.
Recent radioactive treatments can interfere with testing.
It is not intended for general screening purposes and most people will never need to have one done.
No, it is specialized testing that is not offered by every laboratory. Your blood sample will likely need to be sent to a reference laboratory for testing.
No, the receptors for heart and smooth (digestive) muscles are different from skeletal muscles so they are not affected by the formation of AChR binding antibodies.
Most people who have it can live a normal or near normal life with treatment and monitoring. One of the most serious complications is a respiratory myasthenic crisis that can occur when muscles that control breathing are weakened. This can be a medical emergency and often requires hospitalization.
No, the cause of MG is not known and the condition is not preventable.
MG is not contagious, but a pregnant woman with MG can pass some of her AChR antibodies to her fetus. This can cause a newborn to have MG symptoms for several weeks after birth.
As an autoimmune process, no. Some people may inherit a genetic defect that causes congenital myasthenic syndrome, a condition with similar symptoms.
Sources Used in Current Review
(February 19, 2016) National Institute of Neurological Disorders and Stroke. Myasthenia Gravis Factsheet. Available online at http://www.ninds.nih.gov/disorders/myasthenia_gravis/detail_myasthenia_gravis.htm#3153_5. Accessed April 2016.
(Reviewed June 2015) Myasthenia Gravis Foundation of America. Test and Diagnostic Methods. Available online at http://www.myasthenia.org/WhatisMG/TestDiagnosticmethods.aspx. Accessed April 2016.
(March 23, 2016) Shah A. Myasthenia Gravis. Medscape Reference. Available online at http://emedicine.medscape.com/article/1171206-overview. Accessed April 2016.
Meriggioli M, Sanders D. Muscle autoantibodies in myasthenia gravis: beyond diagnosis? Expert Rev Clin Immunol. 2012 Jul; 8(5): 427–438. Available online at http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3505488/. Accessed April 2016.
(July 16, 2012) Penn A, Kaminski H. Myasthenia Gravis Factsheet. Womenshealth.gov. Available online at http://www.womenshealth.gov/publications/our-publications/fact-sheet/myasthenia-gravis.html. Accessed April 2016.
Mayo Clinic Staff (2015 December 24). Myasthenia gravis. Mayo Clinic [On-line information]. Available online at http://www.mayoclinic.org/diseases-conditions/myasthenia-gravis/basics/definition/con-20027124. Accessed April 2016.
Sources Used in Previous Reviews
Kelly, K. (Updated 2012 March 16). Acetylcholine Receptor Antibody. Medscape Reference [On-line information]. Available online at http://emedicine.medscape.com/article/2094601-overview#showall. Accessed April 2013.
(© 1995–2013). Acetylcholine Receptor (Muscle AChR) Binding Antibody, Serum. Mayo Clinic Mayo Medical Laboratories [On-line information]. Available online at http://www.mayomedicallaboratories.com/test-catalog/Overview/8338. Accessed April 2013.
Haven, T. et. al. (2010) An Algorithm for Acetylcholine Receptor Antibody Testing in Patients with Suspected Myasthenia Gravis. Clinical Chemistry v 56 (6) 1028–1040 [On-line information]. Available online at http://www.clinchem.org/content/56/6/1028.full. Accessed April 2013.
Sheth, K. (Updated 2011 June 18). Myasthenia gravis. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/000712.htm. Accessed April 2013.
Sheth, K. (Updated 2011 April 30). Acetylcholine receptor antibody. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003576.htm. Accessed April 2013.
Hill, H. and Haven, T. (2012 August). Acetylcholine Receptor Antibody Testing, For confirmation and monitoring of autoantibodies in patients with myasthenia gravis. ARUP Technical Information [On-line information]. PDF available for download at http://www.aruplab.com/guides/ug/tests/iconpdf_127.pdf. Accessed April 2013.
(2009 December). Facts About Myasthenia Gravis, Lambert-Eaton Myasthenic Syndrome & Congenital Myasthenic Syndromes. Muscular Dystrophy Association [On-line information]. Available online at http://mda.org/publications/facts-about-myasthenia-gravis. Accessed April 2013.
(Updated 2012 August 29). Neurology Myasthenia Gravis Reflexive Panel. The University of Iowa (UIHC) Department of Pathology Laboratory Services Handbook [On-line information]. Available online at http://www.healthcare.uiowa.edu/path_handbook/handbook/test3101.html. Accessed April 2013.
(2013 April 21). Nuromuscular Junction: Myasthenia Gravis. Muscular Dystrophy Australia [On-line information]. Available online at http://www.mda.org.au/Disorders/NMJ/MG.asp. Accessed April 2013.
(© 2012). Acetylcholine Receptor Antibodies. NHS Greater Glasgow and Clyde Information [On-line information]. Available online at http://www.nhsggc.org.uk/content/default.asp?page=s1470_1_2. Accessed April 2013.
(Reviewed 2011 December) Myasthenia Gravis and Acetylcholine Receptor Autoantibodies. Quest Diagnostics Technical Information [On-line information]. Available online at http://www.questdiagnostics.com/testcenter/testguide.action?dc=WP_MyastheniaGravis. Accessed April 2013.
(© 2012). Caring for Children and Supporting Adolescents with Myasthenia Gravis. Myasthenia Gravis Foundation of America [On-line information]. Available online at http://www.myasthenia.org/LinkClick.aspx?fileticket=ygJC0SZLVZ4%3d&tabid=84. Accessed April 2013.
Pagana, K. D. & Pagana, T. J. (© 2011). Mosby's Diagnostic and Laboratory Test Reference 10th Edition: Mosby, Inc., Saint Louis, MO. Pg 6.
Kasper DL, Braunwald E, Fauci AS, Hauser SL, Longo DL, Jameson JL eds, (2005) Harrison's Principles of Internal Medicine, 16th Edition, McGraw Hill, Pp 2518-2521.