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Abstract Details

Performance Evaluation of a Radioimmunoprecipitation Assay for the Detection of N-Type Voltage-gated Calcium Channel Antibodies in Patient and Control Groups
Autoimmune Neurology
P6 - Poster Session 6 (12:00 PM-1:00 PM)
15-009

VGCC antibodies were originally reported in patients with Lambert-Eaton myasthenic syndrome (LEMS) with significant association with malignancy. However, these antibodies are now recognized to be present in diverse neurologic diseases. Antibodies targeting the P/Q-type VGCC are found in most LEMS patients, while the N-type autoantibodies are less frequent but may confer diagnostic and/or prognostic value. There is limited data on the performance characteristics including correlations between methods for the detection of N-type VGCC antibodies.

To assess the performance characteristics of a radioimmunoassay (RIA) to detect N-type voltage-gated calcium channel (VGCC) autoantibodies.

One hundred and ninety-seven (n=197) sera were evaluated. These included 139 patient sera (42 positive and 97 negative for N-type VGCC antibodies) previously tested at Mayo Clinic Laboratories (MCL) and 58 controls (n=28 disease controls and n=30 “self-reported” healthy individuals). Specimens were tested by RIA using solubilized N-VGCC extracted from rabbit brain and labeled with 125I-ω-conotoxin GVIA. Performance of the N-type VGCC antibody RIA was evaluated using in-house established reference ranges (<70 pmol/L=negative, 70-110 pmol/L=indeterminate, >110 pmol/L=positive). Method comparison (accuracy) was determined with the predicate MCL assay based on a tiered positive predictive value (PPV) approach. Assay specificity was assessed using controls.

Qualitative inter-laboratory result comparison based on tiered PPVs of the predicate assay (MCL) demonstrated 100% agreement for results >1.00 nmol/L (71% PPV; n=1), 44% agreement for results of 0.10 – 0.99 nmol/L (24% PPV; n=20) and 14% agreement for results of 0.03-0.10 nmol/L (19% PPV; n=21). Negative results showed 90% agreement (n=97). Clinical specificity was 86% and diagnostic specificity was 100%.

The overall inter-laboratory correlation was comparable; however, challenges were observed for low positive results. Collaborative efforts aimed at assessing the clinical spectrum associated with these antibodies and harmonizing testing are required.

Authors/Disclosures
Thomas Raymond Haven, PhD (ARUP Laboratories)
PRESENTER
Dr. Haven has nothing to disclose.
Bucky K Lozier Bucky K Lozier has nothing to disclose.
Morgan Reynolds No disclosure on file
Christopher Grow No disclosure on file
Anne Tebo Anne Tebo has received personal compensation for serving as an employee of RenalytixAI. The institution of Anne Tebo has received research support from Euroimmun US and Kronus Inc US.
Lisa Kay Peterson, PhD (ARUP Laboratories) The institution of Dr. Peterson has received research support from Kronus.