Test Catalog

Test ID: ACMFS    
Acetylcholine Receptor Modulating Antibody, Flow Cytometry Assay, Serum

Useful For Suggests clinical disorders or settings where the test may be helpful

Diagnosis for autoimmune myasthenia gravis (MG) in adults and children


Distinguishing autoimmune from congenital MG in adults and children or other acquired forms of neuromuscular junction transmission disorders.


This test is a qualitative assay and should not be used for monitoring purposes.

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Fatigable weakness due to impaired postsynaptic transmission at the neuromuscular junction is characteristic of myasthenia gravis (MG). A clinical diagnosis should be supported by electrodiagnostic testing, ie, clinical-electrodiagnosis (EDX). Positive autoimmune serology increases certainty of MG diagnosis but needs to be interpreted in the proper clinical-EDX context with response to anticholinesterase medications supporting the diagnosis. Most cases are autoimmune and are caused by IgG autoantibodies binding to critical postsynaptic membrane molecules (nicotinic muscle acetylcholine receptor [AChR] or its interacting proteins, such as muscle-specific kinase [MuSK]). Serologically, the detection of AChR binding antibody provides the best diagnostic sensitivity. However, the presence of both AChR binding and modulating activity improves diagnostic accuracy. Autoantibody detection frequency is lowest in patients with weakness confined to extraocular muscles (72% are positive for AChR binding antibodies) and highest in patients with generalized weakness due to MG (92% are positive for AChR binding antibodies). In adults with MG and AChR antibodies, approximately 20% will have thymoma and very rarely (<1%) extrathymic cancers. Computed tomography (CT) imaging of the chest is considered the standard of care to evaluate for thymoma.


These results should only be interpreted in the appropriate clinical and electrophysiological context and are not diagnostic in isolation.


Note: Single antibody tests may be requested in the follow-up of patients with positive results previously documented in this laboratory.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

Only orderable as part of a profile. For more information see:

MGLE / Myasthenia Gravis (MG)/Lambert-Eaton Myasthenic Syndrome (LEMS) Evaluation, Serum

MGMR / Myasthenia Gravis Evaluation with MuSK Reflex, Serum

PAVAL / Paraneoplastic, Autoantibody Evaluation, Serum



Interpretation Provides information to assist in interpretation of the test results

This assay shows strong qualitative concordance with the previous modulating assay.


Positive results in this antibody evaluation are indicative of autoimmune myasthenia gravis (MG). These results should be interpreted in the appropriate clinical and electrophysiological context.


The presence of acetylcholine receptor (AChR) modulating antibodies along with AChR binding antibodies as compared to AChR binding antibodies alone, improves the diagnostic accuracy for MG.


In the presence of AChR modulating antibodies, a paraneoplastic basis should be considered with thymoma being the most commonly associated tumor with MG.


Negative results do not exclude the diagnosis of MG. If clinical suspicion remains and symptoms persistent or worsen consider re-testing.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

Positive results are found in some patients with Lambert-Eaton syndrome (LES), paraneoplastic central nervous system (CNS) and peripheral nervous system (PNS) autoimmune disorders and in healthy individuals.


Hemolysis, muscle-relaxant drugs used in the course of general anesthesia, or serum exposed to high ambient temperature can cause false-positive results.

Clinical Reference Recommendations for in-depth reading of a clinical nature

1. Lozier BK, Haven TR, Astill ME, Hill HR: Detection of acetylcholine receptor modulating antibodies by flow cytometry. Am J Clin Pathol. 2015 Feb;143(2):186-192

2. Keefe D, Hess D, Bosco J, et al: A rapid, fluorescence-based assay for detecting antigenic modulation of the acetylcholine receptor on human cell lines. Cytometry Part B. 2009;76B:206-212