Anti-Acetylcholine Receptor Antibody (ACR)

Alternative name: AChRAb
General information ACR are the marker for myasthenia gravis

Myasthenia Gravis is an autoimmune disease where the autoantibodies bind to cholinergic receptors on muscle cells impairing the ability of acetycholine to induce muscular contraction. The disorder may be selective, involving specific groups of muscles. Several clinical subdivisions are recognised.

MG is a rare disease with a prevalence of about 40 per million. 90% of the cases are adults with the peak onset being between 20-40 years. Anti-acetylcholine receptor antibodies are found in 90% of patients with active adult onset generalised myasthaenia gravis. They are pathogenic.

Indication: Highly sensitive and specific marker for generalised Myasthenia Gravis.

A highly sensitive and specific marker for generalised myasthenia gravis (80-90% sensitivity). Low levels of these auto-antibodies have been found in individuals with no apparent symptoms of the disease. Up to 40% patients with pure ocular myasthenia may be antibody negative.

Myasthaenic syndromes of childhood seldom show anti-acetylcholine receptor antibodies.

A group of patients with no detectable serum ACR antibody still have a disorder of transmission very similar clinically to MG. This is usually caused by autoantibodies to Muscle Specific Tyrosine Kinase (see anti-MUSK antibodies).

Sample Serum Separator Tube (SST)
Assay details: Antibodies are detected by radioimmunoassay measuring inhibition of binding of radiolabelled bungarotoxin to human acetylcholine receptor preparations.
Restrictions: Referred test
Reference range: < 5×10-10 mol
Assay range notes: Results are expressed as the concentration of receptor bound to a given dilution of antibody in serum:

  • >500 x 10-10 mol: +++ – very high level of antibody
  • 50-500 x 10-10 mol: ++ – high level of antibody
  • 5-50 x 10-10 mol: + – low level of antibody
  • <5 x 10-10 mol: Negative

The correlation between the concentration of receptor antibody and the severity of clinical symptoms is rather low. However, the correlation is much higher in the individual patient, where changes in symptoms and signs very often coincide with changes in the concentration of antibodies to AchR.

Turnaround time: 28 days
Analysing laboratory: Churchill Hospital Department of Immunology