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Test Code CSF NMO Ab Neuromyelitis Optica (NMO)/Aquaporin-4-IgG Fluorescence-Activated Cell Sorting (FACS) Assay, Spinal Fluid

Useful For

Diagnosis of a neuromyelitis optica spectrum disorder (NMOSD)

 

Diagnosis of autoimmune AQP4 channelopathy

 

Distinguishing NMOSD from multiple sclerosis early in the course of disease

Seattle Children's Hospital Note:

Clinical System Name:  CSF Neuromyelitis (NMO) Ab

Reflex Tests

Test ID Reporting Name Available Separately Always Performed
NMOTC NMO/AQP4 FACS Titer, CSF No No

Testing Algorithm

When the results of this assay require further evaluation, NMOTC / Neuromyelitis Optica (NMO)/Aquaporin-4-IgG Fluorescence-Activated Cell Sorting (FACS) Assay Titer, Spinal Fluid will be performed at an additional charge.

Method Name

Flow Cytometry

Reporting Name

NMO/AQP4 FACS, CSF

Specimen Type

CSF


Necessary Information


Include relevant clinical information, name, phone number, mailing address, and e-mail address (if applicable) of ordering physician.



Specimen Required


Collection Container/Tube: Sterile vial

Specimen Volume: 1 mL


Specimen Minimum Volume

0.5 mL

Specimen Stability Information

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

Reject Due To

Hemolysis

Mild OK; Gross OK

Lipemia

Mild OK; Gross OK

Icterus

Mild OK; Gross OK

Other

NA

Reference Values

Negative

Method Description

NMO-IgG Fluorescence-Activated Cell Sorting Assay (FACS)

 

Human embryonic kidney cells (HEK 293) are transfected transiently with a plasmid (pIRES2-Aequorea coerulescens green fluorescent protein [AcGFP]) encoding both green fluorescent protein (GFP) and AQP4-M1. After 36 hours, the mixed population of cells (transfected expressing AQP4 on the surface and GFP in the cytoplasm and nontransfected lacking AQP4 and GFP) are harvested with short exposure to trypsin. Patient cerebrospinal fluid (CSF) is then added to cells at a 1 in 2 screening dilution. After incubation and washing, the cells are resuspended with AlexaFluor 647-conjugated goat antihuman IgG-gamma specific secondary antibody (Southern Biotech catalog No. 2040-31, 1:2000 in LCBB), held on ice, washed, fixed with 4% paraformaldehyde, and examined with flow cytometry (BD FACSCanto; Becton, Dickinson and Co). Two populations are gated on the basis of GFP expression: positive (high AQP4 expression) and negative (low or no AQP4 expression). The median Alexafluor 647 fluorescence intensity (MFI) for the AcGFP-positive population indicates relative abundance of human IgG potentially bound to AQP4 surface epitopes; MFI for the GFP-negative population indicated nonspecifically-bound IgG. The IgG binding index was calculated as the ratio of the average MFI for duplicate aliquots of each cell population: (MFI GFP positive/MFI GFP negative). We established conservative cutoff IgG binding index values of 2.00 for M1-FACS.

 

If FACS assay is positive at screening dilution, FACS Titer Assay is performed at an additional charge. The patient CSF is titrated to endpoint. The dilution where the IgG-binding index is greater than or equal to 2, is considered the endpoint dilution. If a patient is positive at a 1:2 dilution, but negative at 1:4, the endpoint will be reported as 2.

Day(s) and Time(s) Performed

Monday, Tuesday, Thursday; 6 p.m.

Performing Laboratory

Mayo Medical Laboratories in Rochester

Test Classification

This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the U.S. Food and Drug Administration.

CPT Code Information

86255

86256-NMO/AQP4-IgG FACS titer (if appropriate)

LOINC Code Information

Test ID Test Order Name Order LOINC Value
NMOFC NMO/AQP4 FACS, CSF 46718-3

 

Result ID Test Result Name Result LOINC Value
38325 NMO/AQP4-IgG FACS, CSF 46718-3