Acetylcholine Receptor (AChR)-binding Antibodies

CPT: 83519
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Test Details

Synonyms

  • AChR-binding Antibodies
  • ACRAB
  • Myasthenia Gravis Antibody

Use

In vitro diagnostic semiquantitative determination of autoantibodies against the acetylcholine receptor in human serum and plasma. This assay is the primary test for confirming the diagnosis of acquired myasthenia gravis.1

Limitations

Antibodies are not found in congenital myasthenia.

Methodology

This assay measures antibodies that precipitate solublized muscle AChR that has been complexed with radiolabeled alpha-bungarotoxin (αBTX). Antibodies that bind to the receptor regions that are not sterically blocked by the αBTX are detected.

Contraindications

Recent radioactive scan

Reference Interval

• Negative: 0.00−0.24 nmol/L

• Borderline: 0.25−0.40 nmol/L

• Positive: >0.40 nmol/L

Additional Information

Myasthenia gravis is an acquired disorder of neuromuscular transmission characterized by use-associated muscle weakness and fatigability.1 This condition frequently involves the extraocular muscles and has a strong association with tumor of the thymus (thymoma). The disease has a prevalence of approximately 5 per 100,000 individuals and can occur at any age. In women, the disease usually presents between the ages of 20 and 40 years, while disease onset in men typically occurs later in life.

Autoantibodies to postsynaptic acetylcholine receptors are detectable in the serum of 90% of patients with generalized myasthenia gravis and approximately 70% of patients with ocular myasthenia.1 These autoantibodies interfere with normal neuromuscular function, causing muscle weakness and fatigue. Antibody titers tend to be higher in females and a correlation between antibody titer and degree of muscle weakness has been observed in individual patients. Receptor antibody titers tend to rise several weeks before exacerbations in patients with established myasthenia gravis. Remission after thymectomy is associated with a progressive decline in antibody titers. Consequently, serial measurements of acetylcholine receptor antibodies can be useful in monitoring disease progression as well as the effects of treatment. (Myasthenia gravis is often associated with striational antibody.) AChR-binding antibodies can also be positive in uncomplicated thymoma, Lambert-Eaton myasthenic syndrome, primary lung cancer, and in patients with autoimmune liver disease.1

Specimen Requirements

Specimen

Serum

Volume

1 mL

Minimum Volume

0.3 mL (Note: This volume does not allow for repeat testing.)

Container

Red-top tube or gel-barrier tube

Patient Preparation

No isotopes administered 24 hours prior to venipuncture

Collection

If a red-top tube is used, transfer separated serum to a plastic transport tube.

Storage Instructions

Refrigerate.

Stability Requirements

Temperature

Period

Room temperature

14 days

Refrigerated

14 days

Frozen

14 days

Freeze/thaw cycles

Stable x3

Causes for Rejection

Excessive hemolysis; chylous serum; recently administered radioisotopes; plasma specimen

Clinical Information

Footnotes

1. Griesmann GE, Kryzer TJ, Lennon VA. Autoantibody profiles of myasthenia gravis and Lambert-Eaton myasthenic syndrome. In: Rose NR, Hamilton RG, Detrick B, eds. Manual of Clinical Laboratory Immunology. 6th ed. Washington, DC: ASM Press;2002:1005-1012.

References

Besinger UA, Toyka KV, Hömberg M, Heininger K, Hohlfeld R, Fateh-Moghadam A. Myasthenia gravis: Long-term correlation of binding and bungarotoxin blocking antibodies against acetylcholine receptors with changes in disease severity. Neurology. 1983 Oct; 33(10):1316-1321. 6684226
Bigazzi PE, Burek CL, Rose NR. Antibodies to tissue-specific endocrine, gastrointestinal, and neurological antigens. In: Rose NR, Friedman H, Fahey JL, eds. Manual of Clinical Laboratory Immunology. 3rd ed. Washington, DC: ASM Press;1986:768-770.
Colvin RB, Bhan AK, McCluskey RT, eds. Diagnostic Immunopathology. New York, NY: Raven Press;1988.
Newsom-Davis J. Diseases of the neuromuscular junction. In: Asbury AK, McKhann GM, McDonald WI, eds. Diseases of the Nervous System. Philadelphia, Pa: WB Saunders Co;1992:197-212.
Protti MP, Manfredi AA, Horton RM, Bellone M, Conti-Tronconi BM. Myasthenia gravis: Recognition of a human autoantigen at the molecular level. Immunol Today. 1993 Jul; 14(7):363-368 (review). 8363727
Toyka K. Clinical implementation of anti-acetylcholine receptor antibodies. J Neurol Neurosurg Psychiatry. 1994 Mar; 57(3):396-397. 8158202
Vincent A, Newsom-Davis J. Acetylcholine receptor antibody as a diagnostic test for myasthenia gravis: Results in 153 validated cases and 2967 diagnostic assays. J Neurol Neurosurg Psychiatry. 1985 Dec; 48(12):1246-1252. 4087000

LOINC® Map

Order Code Order Code Name Order Loinc Result Code Result Code Name UofM Result LOINC
085902 AChR Binding Abs, Serum 11034-6 085904 AChR Binding Abs, Serum nmol/L 11034-6

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