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Order Code MGLE Myasthenia Gravis/Lambert-Eaton Myasthenic Syndrome Evaluation, Serum


Ordering Guidance


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 for 1 week and assayed if sufficiently decayed or canceled if radioactivity remains.



Specimen Required


Patient Preparation: For optimal antibody detection, specimen collection is recommended prior to initiation of immunosuppressant medication.

Supplies: Sarstedt Aliquot Tube, 5 mL (T914)

Collection Container/Tube:

Preferred: Red top

Acceptable: Serum gel

Submission Container/Tube: Plastic vial

Specimen Volume: 3 mL

Collection Instructions: Centrifuge and aliquot serum into a plastic vial.


Useful For

Confirming the autoimmune basis of a defect in neuromuscular transmission (eg, myasthenia gravis [MG], Lambert-Eaton myasthenic syndrome [LEMS])

 

Distinguishing LEMS from autoimmune forms of MG

 

Providing a quantitative autoantibody baseline for future comparisons in monitoring a patient's clinical course and response to immunomodulatory treatment

Profile Information

Test ID Reporting Name Available Separately Always Performed
MGLEI MG Lambert-Eaton Interpretation, S No Yes
ARBI ACh Receptor (Muscle) Binding Ab Yes Yes
CCPQ P/Q-Type Calcium Channel Ab No Yes

Reflex Tests

Test ID Reporting Name Available Separately Always Performed
ACMFS AChR Modulating Flow Cytometry, S No No
MUSK MuSK Autoantibody, S Yes No

Testing Algorithm

If acetylcholine receptor (AChR)-binding antibodies are greater than 0.02 nmol/L, then AChR muscle modulating antibody will be performed at an additional charge.

 

If AChR-binding antibodies are 0.02 nmol/L or less, then muscle-specific kinase (MuSK) autoantibody will be performed at an additional charge.

 

If unable to report AChR binding antibody due to interfering substances, then AChR muscle modulating antibody will be performed at an additional charge.

 

If unable to report AChR binding antibody due to interfering substances and AChR muscle modulating antibody is negative, MuSK autoantibody will be performed at an additional charge.

Method Name

ARBI, CCPQ, MUSK: Radioimmunoassay (RIA)

ACMFS: Flow Cytometry

MGLEI: Medical Interpretation

Reporting Name

MG/LEMS Evaluation, S

Specimen Type

Serum

Specimen Minimum Volume

2 mL

Specimen Stability Information

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

Reject Due To

Gross Hemolysis Reject
Gross lipemia Reject
Gross Icterus Reject

Reference Values

Test ID

Reporting name

Methodology

Reference value

MGLEI

MG Lambert-Eaton Interpretation, S

Interpretation

NA

ARBI

ACh Receptor (Muscle) Binding Ab

Radioimmunoassay (RIA)

≤0.02 nmol/L

CCPQ

P/Q-Type Calcium Channel Ab

RIA

≤0.02 nmol/L

Reflex Information:

Test ID

Reporting name

Methodology

Reference value

ACMFS

AChR Modulating Flow Cytometry, S

Flow cytometry

Negative

MUSK

MuSK Autoantibody, S

RIA

≤0.02 nmol/L

Method Description

Radioimmunoassay:

(125)I-labeled recombinant human antigens or labeled receptors are incubated with patient sample. After incubation, anti-human IgG is added to form an immunoprecipitate. The amount of (125)I-labeled antigen in the immunoprecipitate is measured using a gamma-counter. The amount of gamma emission in the precipitate is proportional to the amount of antigen-specific IgG in the sample. Results are reported as units of precipitated antigen (nMol) per L of patient sample.(Griesmann GE, Kryzer TJ, Lennon VA: Autoantibody profiles of myasthenia gravis and Lambert-Eaton myasthenic syndrome. In: Rose NR, Hamilton RG, et al. eds. Manual of Clinical and Laboratory Immunology. 6th ed. ASM Press; 2002:1005-1012; Jones AL, Flanagan EP, Pittock SJ, et al: Responses to and outcomes of treatment of autoimmune cerebellar ataxia in adults. JAMA Neurol. 2015;72[11]:1304-1312. doi:10.1001/jamaneurol.2015.2378)

 

Flow Cytometry:

This method uses flow cytometry to measure the loss of acetylcholine receptor (AChR) molecules expressed on the surface of live cells expressing AChR on the cell surface. The cell line used is an immortalized human rhabdomyosarcoma cell line that expresses endogenous muscle-type nicotinic AChR on its surface. Cells are plated in a 96-well plate and cultured 72 hours prior to the addition of patient sample for an additional 18 to 22 hours to enable internalization of AChR receptors (modulation). Modulation is then stopped by placing cells on ice. The amount of remaining AChRs on the cell surface is measured by flow cytometry. On ice, cells are incubated with a recombinant rat monoclonal antibody against alpha-subunit of the AChR followed by a secondary goat anti-rat IgG antibody conjugated with APC. The amount of AChR on the cell surface is proportional to the median fluorescence intensity (MFI) of allophycocyanin (APC). To calculate the amount of modulation (ie, % loss of AChR) the APC MFI is compared between cells treated with patient sample and cells treated with serum lacking AChR modulating antibodies. Background signal is established in each experiment utilizing cells stained with secondary antibody alone (no patient sera). The percent loss of AChR is calculated as 1-[(Patient MFI-Background MFI)/(Negative calibrator MFI - Background MFI)]*100%.(Unpublished Mayo method)

Day(s) Performed

Profile tests: Monday through Sunday; Reflex tests: Varies

Performing Laboratory

Mayo Clinic Laboratories in Rochester

CPT Code Information

86041

86596

86043 (if appropriate)

86366 (if appropriate)