1
Acetylcholine Receptor (Muscle AChR) Binding
Antibody, Serum
Physiology of muscle contraction:
Normally brain sends signals in form of action potential which travels along the neuron until it reaches
the nerve endings.
Two types of phenomena are involved in processing the nerve impulse: electrical and chemical.
Electrical events propagate a signal within a neuron, and chemical processes transmit the signal from
one neuron to another or to a muscle cell.
The chemical process of interaction between neurons and between neurons and effector cells (muscle)
occur at the end of the axon, in a structure called synapse.
When the action potential of a neuron reaches the neuromuscular junction, the nerve ending secretes
the neurotransmitter acetylcholine (Ach), which diffuses across the synaptic cleft. Acetylcholine travels
through the neuromuscular junction and binds to acetylcholine receptors which are activated and
generate a muscle contraction.
Myasthenia gravis
Myasthenia gravis literally means 'grave muscle weakness'. Myasthenia gravis (MG) is characterized by
weakness and easy fatigability that are relieved by rest and anticholinesterase drugs. The weakness in
most cases results from an autoantibody-mediated loss of functional acetylcholine receptors in the
postsynaptic membrane of skeletal muscle. Demonstration of muscle AChR autoantibodies in a
patient's serum supports the diagnosis of acquired (autoimmune) MG, and quantitation provides a
baseline for future comparisons.
Serum Acetylcholine Receptor (Muscle AChR) Binding Antibody test is used for
 Confirming the diagnosis of MG(myasthenia gravis) and Distinguishing acquired disease (90%
positive) from congenital disease (negative)
 Detecting subclinical MG in patients with thymoma or graft-versus-host disease
 Monitoring disease progression in MG or response to immunotherapy
 An adjunct to the test for P/Q-type calcium channel binding antibodies as a diagnostic aid for
LES or primary lung carcinoma
Clinical Information
 Muscle AChR antibodies are not found in congenital forms of MG and are uncommon in
neurologic conditions other than acquired MG.
 The exception is patients with paraneoplastic autoimmune neurological disorders, and LambertEaton myasthenic syndrome (LES) with or without cancer (13% of LES patients have positive
results for muscle AChR binding or striational antibodies).
 Patients with autoimmune liver disease are also frequently seropositive.
 The assay for muscle AChR binding antibodies is considered a first-order test for the laboratory
diagnosis of MG, and for detecting "subclinical MG" in recipients of D-penicillamine, in patients
with thymoma without clinical evidence of MG, and in patients with graft-versus-host disease.
2
Lambert–Eaton myasthenic syndrome (LEMS,)
This is a rare autoimmune disorder that is characterised by muscle weakness of the limbs.
It is the result of antibodies formed against presynaptic voltage-gated calcium channels in
the neuromuscular junction. Around 60% of those with LEMS have an underlying malignancy, most
commonly small cell lung cancer; it is therefore regarded as a paraneoplastic syndrome.
Specimen Type Serum
Specimen Required Container/Tube: Plain, red-top tube(s) or serum gel tube(s)
Specimen Volume: 2 mL of serum
Reject Due To
Specimens other than
Serum
Hemolysis
Mild OK; Gross reject
Lipemia
Mild OK; Gross reject
Icteric
Mild OK; Gross reject
Transport Temperature
Refrig <14 days\Ambient <72 hours OK\Frozen OK
Reference Values
< or =0.02 nmol/L
Interpretati0n
 Values >0.02 nmol/L are consistent with a diagnosis of acquired MG, provided that clinical/
electrophysiological criteria support that diagnosis.
 The assay for muscle AChR binding antibodies is positive in approximately 90% of
nonimmunosuppressed patients with generalized MG.
 The frequency of antibody detection is lower in MG patients with weakness clinically restricted
to ocular muscles (71%), and antibody titers are generally low in ocular MG (e.g. 0.03-1.0
nmol/L).
 Results may be negative in the first 12 months after symptoms of MG appear or during
immunosuppressant therapy.
Note: In general, there is not a close correlation between antibody titer and severity of weakness, but in
individual patients, clinical improvement is usually accompanied by a decrease in titer.
Cautions
Positive results for muscle AChR binding or striational antibodies are found in 13% of patients with LES.
This does not mean that MG and LES co-exist. Antibodies to P/Q type calcium channels are found in 95%
of LES patients, but not in MG, except in very rare paraneoplastic cases related to small-cell lung
carcinoma.
Positive results are frequently found with autoimmune liver disease.
Magnitude of the result is not useful for predicting severity of MG.
REFERENCES:

Hirokazu Hara,” Kyozo Hayashi, Kiyoe Ohta,’ Nobuyuki Itoh, Hiroshi Nishitani, and Mitsuhiro
Ohta” Detection and Characterization of Blocking-Type Anti-Acetylcholine Receptor Antibodies
in Sera from Patients with Myasthenia Gravis Clinical chemistry, vol. 39, no. 10, 1993 2053
3

Thomas R. Haven, Mark E. Astill, Brian M . Pasi, James B. Carper, Lily L. Wu, Anne E. Tebo, and
Harry R. Hill An Algorithm for Acetylcholine Receptor Antibody Testing in Patients with
Suspected Myasthenia Gravis Clin. Chem., Jun 2010; 56: 1028 - 1029.

Juel VC, Massey JM; Myasthenia gravis. Orphanet J Rare Dis. 2007 Nov 6;2(1):44.

A Vincent, J Newsom-Davis Acetylcholine receptor antibody as a diagnostic test for myasthenia
gravis: results in 153 validated cases and 2967 diagnostic assays. J Neurol Neurosurg
Psychiatry 1985;48:1246-1252

J Rees Paraneoplastic syndromes: when to suspect, how to confirm, and how to manage. J
Neurol Neurosurg Psychiatry. 2004 June; 75(Suppl 2): ii43–ii50.