Medical term:

AChR

Acetylcholine Receptor Antibody

Synonym/acronym: AChR (AChR-binding antibody, AChR-blocking antibody, and AChR-modulating antibody).

Common use

To assist in confirming the diagnosis of myasthenia gravis (MG).

Specimen

Serum (1 mL) collected in a red-top tube.

Normal findings

(Method: Radioimmunoassay) AChR-binding antibody: Less than 0.4 nmol/L, AChR-blocking antibody: Less than 25% blocking, and AChR-modulating antibody: Less than 30% modulating.

Description

Normally when impulses travel down a nerve, the nerve ending releases a neurotransmitter called acetylcholine (ACh), which binds to receptor sites in the neuromuscular junction, eventually resulting in muscle contraction. Once the neuromuscular junction is polarized, ACh is rapidly metabolized by the enzyme acetylcholinesterase. When present, AChR-binding antibodies can activate complement and create a complex of ACh, AChR-binding antibodies, and complement. This complex renders ACh unavailable for muscle receptor sites. If AChR—binding antibodies are not detected, and myasthenia gravis (MG) is strongly suspected, AChR-blocking and AChR-modulating antibodies may be ordered. AChR-blocking antibodies impair or prevent ACh from attaching to receptor sites on the muscle membrane, resulting in poor muscle contraction. AChR-modulating antibodies destroy AChR sites, interfering with neuromuscular transmission. The lack of ACh bound to muscle receptor sites results in muscle weakness. Antibodies to AChR sites are present in 90% of patients with generalized MG and in 55% to 70% of patients who either have ocular forms of MG or are in remission. Approximately 10% to 15% of people with confirmed MG do not demonstrate detectable levels of AChR-binding, -blocking, or -modulating antibodies. MG is an acquired autoimmune disorder that can occur at any age. Its exact cause is unknown, and it seems to strike women between ages 20 and 40 years; men appear to be affected later in life than women. It can affect any voluntary muscle, but muscles that control eye, eyelid, facial movement, and swallowing are most frequently affected. Antibodies may not be detected in the first 6 to 12 months after the first appearance of symptoms. MG is a common complication associated with thymoma. The relationship between the thymus gland and MG is not completely understood. It is believed that miscommunication in the thymus gland directed at developing immune cells may trigger the development of autoantibodies responsible for MG. Remission after thymectomy is associated with a progressive decrease in antibody level. Other markers used in the study of MG include striational muscle antibodies, thyroglobulin, HLA-B8, and HLA-DR3. These antibodies are often undetectable in the early stages of MG.

This procedure is contraindicated for

high alert Appropriate timing when scheduling multiple studies should be taken into consideration. Recent radioactive scans or radiation within 1 wk of the test can invalidate test results when radioimmunoassay is the test method.

Indications

Confirm the presence but not the severity of MG
Detect subclinical MG in the presence of thymoma
Monitor the effectiveness of immunosuppressive therapy for MG
Monitor the remission stage of MG

Potential diagnosis

Increased in

Autoimmune liver disease
Generalized MG (Defective transmission of nerve impulses to muscles evidenced by muscle weakness. It occurs when normal communication between the nerve and muscle is interrupted at the neuromuscular junction. It is believed that miscommunication in the thymus gland directed at developing immune cells may trigger the development of autoantibodies responsible for MG.)
Lambert-Eaton myasthenic syndrome
Primary lung cancer
Thymoma associated with MG (Defective transmission of nerve impulses to muscles evidenced by muscle weakness. It occurs when normal communication between the nerve and muscle is interrupted at the neuromuscular junction. It is believed that miscommunication in the thymus gland directed at developing immune cells may trigger the development of autoantibodies responsible for MG.)

Decreased in

(The thymus gland produces the T lymphocytes responsible for cell-mediated immunity. T cells also help control B-cell development for the production of antibodies. T-cell response is directed at cells in the body that have been infected by bacteria, viruses, parasites, fungi, or protozoans. T cells also provide immune surveillance for cancerous cells. Removal of the thymus gland is strongly associated with a decrease in AChR antibody levels.)

Critical findings

N/A

Interfering factors

Drugs that may increase AChR levels include penicillamine (long-term use may cause a reversible syndrome that produces clinical, serological, and electrophysiological findings indistinguishable from MG).
Biological false-positive results may be associated with amyotrophic lateral sclerosis, autoimmune hepatitis, Lambert-Eaton myasthenic syndrome, primary biliary cirrhosis, and encephalomyeloneuropathies associated with carcinoma of the lung.
Immunosuppressive therapy is the recommended treatment for MG; prior immunosuppressive drug administration may result in negative test results.
Recent radioactive scans or radiation within 1 wk of the test can interfere with test results when radioimmunoassay is the test method.

Nursing Implications and Procedure

Potential nursing problems

Problem	Signs & Symptoms	Interventions
Urination (Related to neurogenic bladder; spastic bladder; associated with disease process)	Urinary retention; urinary frequency; urinary urgency; pain and abdominal distention; urinary dribbling	Assess amount of fluid intake as it may be necessary to limit fluids to control incontinence; assess risk of urinary tract infection with limiting oral intake; begin bladder training program; teach catheterization techniques to family and patient self-catheterization
Self-care (Related to spasticity; altered level of consciousness; paresis; increasing weakness; paralysis)	Difficulty fastening clothing; difficulty performing personal hygiene; inability to maintain appropriate appearance; difficulty with independent mobility; declining physical function	Reinforce self-care techniques as taught by occupational therapy; ensure the patient has adequate time to perform self-care; encourage use of assistive devices to maintain independence; assess ability to perform ADLs; provide care assistance appropriate to degree of disability while maintaining as much independence as possible
Mobility (Related to weakness; tremors; spasticity)	Unsteady gait; lack of coordination; difficult purposeful movement; inadequate range of motion	Assess gait; assess muscle strength; assess weakness and coordination; assess physical endurance and level of fatigue; assess ability to perform independent ADLs; assess ability for safe, independent movement; identify need for assistive device; encourage safe self-care
Pain (Related to motor and sensory nerve damage associated with disease process)	Self-report of pain; emotional symptoms of distress; crying; agitation; facial grimace; moaning; verbalization of pain; rocking motions; irritability; disturbed sleep; diaphoresis; altered blood pressure and heart rate; nausea; vomiting	Keep the immediate environment cool to decrease aggravating MG symptoms; use passive or active range of motion to decrease muscle tightness; administer analgesics, tranquilizers, antispasmodics, and neuropathic pain medication, as ordered

Pretest

Positively identify the patient using at least two unique identifiers before providing care, treatment, or services.
Patient Teaching: Inform the patient that the test is used to identify antibodies responsible for decreased neuromuscular transmission and associated muscle weakness.
Obtain a history of the patient’s complaints, including a list of known allergens, especially allergies or sensitivities to latex, and any prior complications with general anesthesia.
Obtain a history of the patient’s musculoskeletal system, symptoms, and results of previously performed laboratory tests and diagnostic and surgical procedures.
Note any recent procedures that can interfere with test results.
Obtain a list of the patient’s current medications, including herbs, nutritional supplements, and nutraceuticals (see Effects of Natural Products on Laboratory Values).
Review the procedure with the patient. Inform the patient that specimen collection takes approximately 5 to 10 min. Address concerns about pain and explain that there may be some discomfort during the venipuncture.
Sensitivity to social and cultural issues, as well as concern for modesty, is important in providing psychological support before, during, and after the procedure.
Note that there are no food, fluid, or medication restrictions unless by medical direction.

Intratest

Potential complications: N/A
Avoid the use of equipment containing latex if the patient has a history of allergic reaction to latex.
Instruct the patient to cooperate fully and to follow directions. Direct the patient to breathe normally and to avoid unnecessary movement.
Observe standard precautions, and follow the general guidelines in Patient Preparation and Specimen Collection. Positively identify the patient, and label the appropriate specimen container with the corresponding patient demographics, initials of the person collecting the specimen, date, and time of collection. Perform a venipuncture.
Remove the needle and apply direct pressure with dry gauze to stop bleeding. Observe/assess venipuncture site for bleeding or hematoma formation and secure gauze with adhesive bandage.
Promptly transport the specimen to the laboratory for processing and analysis.

Post-Test

Inform the patient that a report of the results will be made available to the requesting health-care provider (HCP), who will discuss the results with the patient.
Recognize anxiety related to test results, and be supportive of activity challenges related to lack of neuromuscular control, anticipated loss of independence, and fear of death. It is important to note that a diagnosis of MG should be based on abnormal findings from two different diagnostic tests. These tests include AChR antibody assay, anti-MuSK antibody assay (an antibody which is produced in 40% to 70% of the remaining 15% who have MG but test negative for AChR antibody), edrophonium test (which involves injection of edrophonium or tensilon, a medication that temporarily blocks the degradation of acetylcholine, allowing normal measurable neuromuscular transmission that dissipates as the effects of the injection wear off), repetitive nerve stimulation (small pulses of electricity are repeatedly sent to specific muscles by way of electrodes to measure a decrease in response due to muscle weakening), and single-fiber electromyography (see EMG monograph for more detailed information). Discuss the implications of positive test results on the patient’s lifestyle. Positive test results may lead to testing for other conditions associated with MG.
Thyrotoxicosis may occur in conjunction with MG; related thyroid testing may be indicated. MG patients may also produce antibodies, such as antinuclear antibody and rheumatoid factor, not primarily associated with MG that demonstrate measurable reactivity.
Evaluate test results in relation to future general anesthesia, especially regarding therapeutic management of MG with cholinesterase inhibitors. Succinylcholine-sensitive patients may be unable to metabolize the anesthetic quickly, resulting in prolonged or unrecoverable apnea.
Provide contact information, if desired, for the Myasthenia Gravis Foundation of America (www.myasthenia.org) and the Muscular Dystrophy Association (www.mdausa.org).
Depending on the results of this procedure, additional testing may be performed to evaluate or monitor progression of the disease process and determine the need for a change in therapy. If a diagnosis of MG is made, a computed tomography (CT) scan of the chest should be performed to rule out thymoma. Evaluate test results in relation to the patient’s symptoms and other tests performed.
Patient Education
- Discuss the implications of positive test results on the patient’s lifestyle.
- Provide teaching and information regarding the clinical implications of the test results, as appropriate.
- Educate the patient regarding access to counseling services.
- Reinforce information given by the patient’s health-care provider (HCP) regarding further testing, treatment, or referral to another HCP.
- Answer any questions or address any concerns voiced by the patient or family.
- Teach family to place self-care items within the patients reach to promote as much independence in care as possible.
- Teach the family and patient that assistive devices can improve quality of life and decrease injury risk.
Expected Patient Outcomes
- Knowledge
- The patient and family verbalize understanding that spasms can be decreased by adhering to recommended physical therapy.
- The patient and family describe the necessity to promote independent self-care while seeking assistance as necessary to prevent injury.
- Skills
- The patient and family demonstrate the ability to perform passive and active range of motion activities.
- The patient and family demonstrate how to apply splints to hands to help control hand spasms.
- Attitude
- The patient and family set personal goals regarding performance of self-care activities that are in realistic proportion to disease progression.
- The patient and family accept the physical limitations related to the disease process.

Related Monographs

Related tests include ANA, antithyroglobulin and antithyroid peroxidase antibodies, CT chest, myoglobin, pseudocholinesterase, RF, TSH, and total T₄.
Refer to the Musculoskeletal System table at the end of the book for related tests by body system.

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