Ordering Recommendation

Screening test for voltage-gated potassium channel (VGKC) antibody receptor complex-associated autoantibodies with test reflex to CASPR2 and LGI1 antibodies. Antibodies are associated with acquired neuromyotonia, limbic encephalitis, painful neuropathy, Morvan syndrome, and rare tumors (eg, thymoma, small-cell lung cancer).

Mnemonic
VGKC R
Methodology

Quantitative Radioimmunoassay/Semi-Quantitative Indirect Fluorescent Antibody

Performed

Tue

Reported

1-8 days

New York DOH Approval Status
This test is New York DOH approved.
Specimen Required
Patient Preparation
Collect

Plain red or serum separator tube.

Specimen Preparation

Separate serum from cells within 1 hour. Transfer 4 mL serum to an ARUP Standard Transport Tube. (Min: 0.5 mL)

Storage/Transport Temperature

Refrigerated.

Unacceptable Conditions

Plasma. Severely lipemic or icteric specimens.

Remarks
Stability

After separation from cells: Ambient: 72 hours; Refrigerated: 2 weeks; Frozen: 1 month (avoid repeated freeze/thaw cycles)

Reference Interval
Test Number
Components
Reference Interval
2004890 Voltage-Gated Potassium Channel (VGKC) Antibody, Serum
Negative 31 pmol/L or less
Indeterminate 32-87 pmol/L
Positive 88 pmol/L or greater

2009456 Leucine-Rich, Glioma-Inactivated Protein 1 Antibody, IgG with Reflex to Titer, Serum Less than 1:10
2009452 Contactin-Associated Protein-2 Antibody, IgG with Reflex to Titer, Serum Less than 1:10

Interpretive Data

Voltage-Gated Potassium Channel (VGKC) antibodies are associated with neuromuscular weakness as found in neuromyotonia (also known as Issacs syndrome) and Morvan syndrome. VGKC antibodies are also associated with paraneoplastic neurological syndromes and limbic encephalitis; however, VGKC antibody-associated limbic encephalitis may be associated with antibodies to leucine-rich, glioma-inactivated 1 protein (LGI1) or contactin-associated protein-2 (CASPR2) instead of potassium channel antigens. A substantial number of VGKC-antibody positive cases are negative for LGI1 and CASPR 2 IgG autoantibodies, not all VGKC complex antigens are known. The clinical significance of this test can only be determined in conjunction with the patient's clinical history and related laboratory testing.

Compliance Category

Laboratory Developed Test (LDT)

Note

If VGKC is Indeterminate or Positive, LGI1 Antibody IgG and CASPR2 Antibody IgG will be added. If LGI1 antibody IgG is positive, then LGI1 antibody IgG titer will be added. If CASPR2 antibody IgG is positive, then CASPR2 antibody IgG titer will be added. Additional charges apply.

Hotline History
N/A
CPT Codes

83519; if reflexed add 86255 x2; if reflexed add 86256 per titer

Components
Component Test Code* Component Chart Name LOINC
2004890 Voltage-Gated Potassium Channel Ab, Ser 41871-5
* Component test codes cannot be used to order tests. The information provided here is not sufficient for interface builds; for a complete test mix, please click the sidebar link to access the Interface Map.
Aliases
Voltage-Gated Potassium Channel (VGKC) Antibody with Reflex to LGI1 and CASPR2 Screen and Titer, Serum