Acetylcholine Receptor Binding Ab (ARBI)

Test Code: ACRB

Overview
Ordering
Specimen
Performing
Clinical/Interpretive
Contacts
Coding

Synonyms/Keywords

Acetylcholine Receptor (Muscle AChR) Antibodies, AChR (Acetylcholine Receptor), Anti -Neuromuscular Junction Receptor Antibodies, Myasthenia Gravis Antibodies

Useful For

A first-order test for the laboratory diagnosis of myasthenia gravis (MG)

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

Distinguishing acquired disease (90% positive) from congenital disease (negative)

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 Lambert-Eaton myasthenic syndrome (LES) or primary lung carcinoma

Specimen Requirements

Specimen Type	Preferred Container/Tube	Acceptable Container/Tube	Specimen Volume	Specimen Minimum Volume (allows for 1 repeat)	Pediatric Minimum Volume (no repeat)
Serum	Red Top Tube (RTT)	Serum Separator Tube (SST)	1.5 mL	1.0 mL

Acceptable Specimen Types

Patient Preparation: This test should not be requested in patients who have recently received radioisotopes, therapeutically or diagnostically, because of potential assay interference. The specific waiting period before specimen collection will depend on the isotope administered, the dose given and the clearance rate in the individual patient. Specimens will be screened for radioactivity prior to analysis. Radioactive specimens received in the laboratory will be held 1 week and assayed if sufficiently decayed, or canceled if radioactivity remains.

Specimen Stability Information

Specimen Type	Temperature	Time
Serum	Refrigerated (preferred)	28 days
	Ambient	72 hours
	Frozen	28 days

Rejection Criteria

Gross hemolysis
Gross lipemia
Gross icterus

Performing Laboratory Information

Performing Location	Day(s) Test Performed	Analytical Time	Methodology/Instrumentation
Mayo Medical Laboratories	Monday through Sunday	3 days	Radioimmunoassay (RIA)

Reference Lab

Mayo Clinic Laboratories

Reference Range Information

< or = 0.02 nmol/L

Interpretation

Values >0.02 nmol/L are consistent with a diagnosis of acquired myasthenia gravis (MG), provided that clinical and electrophysiological criteria support that diagnosis.

The assay for muscle acetylcholine receptor (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 (eg, 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 follow up of seronegative patients with adult-acquired generalized MG, 17.4% seroconvert to positive at 12 months (ie, seronegativity rate at 12 months is 8.4%). Of persistently seronegative patients, 38% have muscle-specific kinase (MuSK) antibody.

Sera of nonmyasthenic subjects bind per liter 0.02 nmol or less of muscle AChR complexed with (125)I-labeled-alpha-bungarotoxin.

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.

Outreach CPTs

CPT	Modifier (if needed)	Quantity	Description	Comments
83519