VGKC Antibody w/ Reflex, Serum (Sendout)

General Information

Lab Name

Lab Code

RVGKCA

Epic Name

VGKC Antibody w/ Reflex, Serum (Sendout)

External Test Id

2009463

Description

Ordering Recommendation: Screening test for voltage-gated potassium channel (VGKC) antibody receptor complex-associated autoantibodies with reflex to CASPR2 and LGI1 antibodies.

Patients with LGI1-antibodies have a limbic encephalitis, often with hyponatremia, and about half of the patients have typical faciobrachial dystonic seizures. Caspr2-antibodies cause a more variable syndrome of peripheral or central nervous system symptoms, almost exclusively affecting older males. Half of the VGKC-positive patients lack antibodies to both LGI1 and Caspr2. The clinical significance of VGKC-only antibodies in the absence of LGI1 and CASPR2 antibodies is unclear.¹

Test Algorithm: If VGKC is indeterminate or positive, LGI1 and CASPR2 IgG Antibodies, Serum (Sendout) [RRLGC2] will be performed at additional charge. If either of the reflex tests are positive, then titer(s) will be added at additional charge.

References

van Sonderen A, Schreurs MW, Wirtz PW, Sillevis Smitt PA, Titulaer MJ. From VGKC to LGI1 and Caspr2 encephalitis: The evolution of a disease entity over time. Autoimmun Rev. 2016 Oct;15(10):970-4. doi: 10.1016/j.autrev.2016.07.018. Epub 2016 Jul 30. PMID: 27485013.

Synonyms

2009463, CASPR2, LGI-1, LGI1, VGKC Antibody

Components

Code	Name
RVGKCR	VGKC Antibody, Serum

Interpretation

Method

Quantitative Radioimmunoassay/Semi-Quantitative Indirect Fluorescent Antibody

Reference Range

See individual components

Ref. Range Notes

Reference Ranges:

Negative:	</= 31 pmol/L
Indeterminate:	32-87 pmol/L
Positive:	>/= 88 pmol/L

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.

References

van Sonderen A, Schreurs MW, Wirtz PW, Sillevis Smitt PA, Titulaer MJ. From VGKC to LGI1 and Caspr2 encephalitis: The evolution of a disease entity over time. Autoimmun Rev. 2016 Oct;15(10):970-4. doi: 10.1016/j.autrev.2016.07.018. Epub 2016 Jul 30. PMID: 27485013.

Ordering & Collection

Specimen Type: Blood
Collection: 10 mL blood in in RED TOP tube or GOLD SST
Handling Instructions: Centrifuge and separate serum from cells within one hour of collection. Refrigerate serum while awaiting transport. Ship with an ice pack.

Stability: Refrigerated (preferred): 2 weeks; Frozen: 1 month; Ambient: 72 hours.

Unacceptable Conditions: Plasma; severely lipemic or icteric samples. Avoid repeated freeze/thaw cycles.
Quantity: Requested: 4 mL Serum
Minimum: 0.5 mL serum

Processing

Receiving Instructions

Centrifuge and separate serum from cells within one hour of collection. Refrigerate serum.

Sendouts:

Order ARUP Test: 2009463
Interfaced: Yes [Interface: 602; Department: ARPR]

Stability: Refrigerated (preferred): 2 weeks; Frozen: 1 month; Ambient: 72 hours.

Unacceptable Conditions: Plasma; severely lipemic or icteric samples. Avoid repeated freeze/thaw cycles.

Misc Sendout

Performance

Lab Department

Sendouts ARUP Lab (RF)(ARPR)

Frequency

Performed: Tuesday. Reported: 1-8 days from sample receipt at ARUP Laboratories.

Available STAT?

Performing Location(s)

Sendout	ARUP Laboratories, Inc. 800-522-2787 500 Chipeta Way Salt Lake City, UT 84108

Billing & Coding

CPT Codes: 83519
LOINC: 41871-5