Acetylcholine receptor antibody panel
(ACHR Ab, Anti-ACHR antibody)
🔹Type of test Blood Normal findings ACh receptor (muscle) binding antibodies:
✏< 0.02 nmol/L ACh receptor (muscle) modulating antibodies
✏0%-20% (reported as % loss of ACAR) Striational (striated muscle) antibodies
✏< 1:60 Test explanation and related physiology .
🔹These antibodies may cause blocks in neuromuscular transmission by interfering with the binding ofacetylcholine (ACh) to AC receptor (ACR) sites on the muscle membrane, thereby preventing muscle contraction.
🔹 This phenomenon characterizes myasthenia gravis (MG).
🔹 Antibodies to ACER occur in more than 85% of patients with acquired MG.
🔹Lower levels are seen in patients with ocular MG only.
🔹 The presence of these antibodies is virtually diagnostic of MG, but a negative test result does not exclude the disease.
🔹 The measured titers do not correspond well with the severity of MG in different patients.
🔹In an individual patient, however, antibody levels are particularly useful in monitoring response to therapy.
🔹As the patient improves, antibody titers decrease. In adults with MG, there is at least a 20% occurrence of thymoma or other neoplasm.
🔹Neoplasms are an endogenous source of the antigens driving production of ACHR autoantibodies.
🔹The ACHR-binding antibody can activate complement and lead to loss of ACER.
1) The AChR-modulating antibody causes receptor endocytosis, resulting in loss of ACAR expression, which correlates most closely with clinical severity of disease.
🎯It is the most sensitive test. A positive modulating antibody test result may indicate subclinical MG, contraindicating the use of curare-like drugs during surgery.
2) The AChR-blocking antibody may impair binding of Ach to the receptor, leading to poor muscle contraction.
🎯It is the least sensitive test (positive in only 61% of patients with MG)3) Antistriated muscle antibody (striated muscle antibody, LOG) titers greater than or equal to 1:80 are suggestive of myasthenia.
🎯This antibody is detectable in 30% to 40% of anti-AChR-negative patients (particularly those with bulbar symptoms only). However, striated muscle antibody can be found in rheumatic fever, myocardial infarction, and a variety of postcardiotomy states.
🎯✏ Interfering factors 🎯✏
🔎📌 False-positive results may occur in patients with:_
- amyotrophic lateral sclerosis who have been treated with cobra venom.
- penicillamineinduced or Lambert-Eaton myasthenic syndrome.
- autoimmune liver disease
- Drugs that may cause increased levels include muscle paralytic medicines (succinylcholine) and snake venom.
5- Immunosuppressive drugs may suppress the formation of
these antibodies in patients with subclinical MG.
🎯 Abnormal findings 🎯
A Increased titer levels:
1- Myasthenia gravis
2- Ocular myasthenia gravis