Acetylcholine Receptor (AChR) Binding Antibody
Looks for antibodies that attack the acetylcholine receptor on muscle cells. A positive result is linked to myasthenia gravis, a condition that causes muscle weakness.
AI-verified against cited sources. Awaiting expert reviewAlso called AChR binding AbLOINC 11034-6
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What it is
Muscles take their signals from nerves through a chemical called acetylcholine, which lands on receptors on the muscle surface. In myasthenia gravis, the immune system makes antibodies that attack these receptors. The signal then gets through less well, and muscles tire easily. This blood test measures how much of that antibody is in your serum. Labs use a radioimmunoassay (a test that uses a tiny amount of radioactive tracer) and report the result in nmol/L.
Why it matters
It is usually the first antibody test when a clinician suspects myasthenia gravis. About 85 in 100 people with generalized myasthenia gravis have these antibodies, and about half of people whose weakness is limited to the eyes do. A positive result, together with symptoms and nerve and muscle tests, can support the diagnosis. A negative result does not rule it out, because about 1 in 10 people with the condition have no antibody found on standard tests. The number on its own is not a good way to compare how severe the condition is from one person to another.
If it’s high
A result above your lab's cutoff is reported as positive. These antibodies are strongly linked to myasthenia gravis and are only rarely found in other conditions. Your clinician reads the result together with your symptoms and other tests.
Common causes
- Myasthenia gravis, an autoimmune condition that causes muscle weakness that gets worse with activity
- A thymoma (a growth in the thymus gland), which can come with these antibodies even in people without myasthenia symptoms
- Rarely, other autoimmune conditions
What can help
- Ask your clinician how this result fits with your symptoms and your nerve and muscle tests
- Ask whether a scan of the thymus gland is needed
- Ask whether other myasthenia antibody tests would be useful for you
Usual ranges
What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.
For adults: 0–0.3 nmol/L. Source: Quest Diagnostics, ARUP Laboratories, Mayo Clinic Laboratories.
- Adults (this one applies)0–0.3 nmol/L
Sources: Quest Diagnostics, ARUP Laboratories, Mayo Clinic Laboratories
Quest Diagnostics result categories (assay-specific)
- Negativebelow 0.31 nmol/L
- Equivocal0.31 to under 0.5 nmol/L
- Positive0.5 and above nmol/L
What can affect your result
- Assay and lab: cutoffs range from about 0.02 to 0.4 nmol/L between labs, so compare with your own lab's range
- Timing: the sample is best drawn before immune-suppressing medicine or IVIG is started
- Type of myasthenia gravis: antibodies are found less often when weakness is limited to the eyes
- Recent radioisotope scans or treatment, which can interfere with the test
- Treatment over time, which can change antibody levels
- Recent nuclear medicine scans or radioisotope treatment can interfere with this radioimmunoassay. Mayo Clinic Laboratories checks samples for radioactivity and may hold or cancel the test.
- Mayo Clinic Laboratories recommends collecting the sample before starting immune-suppressing medicine or intravenous immunoglobulin (IVIG), because treatment can change antibody detection.
- Samples that are grossly hemolyzed, very lipemic or contaminated with microbes may be rejected (Quest). ARUP also does not accept plasma.
- Results from different assays and labs are not interchangeable, because cutoffs differ.
Levels change gradually with treatment. Your specialist decides when a repeat is useful.
When to talk to a clinician
Call your local emergency number if you have trouble breathing or swallowing, or your weakness suddenly gets worse. Trouble breathing from muscle weakness needs emergency care. A positive antibody result on its own is not an emergency, but talk with your clinician soon about what it means for you, especially if you have drooping eyelids, double vision, or weakness that gets worse with activity.
Questions you could ask
- Which test method and cutoff did my lab use, so I can compare future results?
- What does this result mean alongside my symptoms and my nerve and muscle tests?
- Do I need a scan to look at my thymus gland?
- Should I see a specialist in nerve and muscle conditions?
- If my symptoms continue, what other tests could help?
- Should this test be repeated, or would other antibody tests be useful?
Questions people ask
My result is negative, but my clinician still suspects myasthenia gravis. Is that possible?
Yes. About 1 in 10 people with myasthenia gravis have no antibody found on standard tests, and only about half of people whose weakness is limited to the eyes test positive. Specialists may repeat the test or use other antibody tests, along with nerve and muscle tests.
Why does my report use a different cutoff from someone else's?
Labs use different test kits and calibration. For example, Mayo Clinic Laboratories uses 0.02 nmol/L, Quest uses 0.30 nmol/L and ARUP uses 0.4 nmol/L as the top of the negative range. Use the cutoff on your own report, and avoid comparing numbers between labs.
Does a higher number mean my myasthenia gravis is worse?
Not when you compare one person with another. Within one person, changes over time may follow symptoms and response to treatment, which is why a specialist may sometimes repeat the test.
Show the science and sources
For clinicians and researchers
AChR binding antibodies are usually measured by radioimmunoassay (radioimmunoprecipitation), in which human AChR, from muscle or from AChR-expressing cell lines, is labeled with 125I-alpha-bungarotoxin and precipitated with patient IgG. This assay has a specificity of about 99% and a sensitivity of about 85% in generalized MG and about 50% in ocular MG. ELISA is less sensitive, and cell-based assays can detect antibodies missed by the standard assay but are mostly qualitative (Lazaridis 2020). Binding antibodies can activate complement. Blocking antibodies impair acetylcholine binding. Modulating antibodies cause receptor endocytosis and, according to ARUP, correlate most closely with clinical severity. About 10 to 15% of people with confirmed MG have no measurable binding, blocking or modulating antibody (ARUP), and about 6% have MuSK antibodies (Lazaridis 2020). Across patients the titer does not correlate with severity, but within one patient it tracks symptoms and treatment response, so serial samples are useful. A suspected MG patient who is seronegative at first should be retested (Lazaridis 2020). Cutoffs are assay-specific: Mayo 0.02 nmol/L or less (RIA, with reflex to AChR modulating antibody when above 0.02 and to MuSK when 0.02 or below), Quest 0.30 or less negative, 0.31 to 0.49 equivocal and 0.50 or more positive, and ARUP 0.4 or less negative and 0.5 or more positive. Mayo reports its result under LOINC 97558-1, and ARUP under 11034-6.
LOINC 11034-6 (primary), 97558-1, 11560-0, 43624-6. Specimen: serum.
Sources
- Acetylcholine Receptor Binding Antibody (test code 206), Quest Diagnostics
- Acetylcholine Receptor Binding Antibody (test 0080009), ARUP Laboratories
- Myasthenia Gravis Evaluation with Muscle-Specific Kinase (MuSK) Reflex, Serum (test MGMR), Mayo Clinic Laboratories
- Autoantibody Specificities in Myasthenia Gravis; Implications for Improved Diagnostics and Therapeutics, Frontiers in Immunology (2020)
- Myasthenia Gravis Tests, MedlinePlus, National Library of Medicine
AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.