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Comparative Sensitivities and Specificities of Immunohistochemical and Immunoprecipitation Assays

Andrew McKeon, MB, MRCPI; James P. Fryer, MS; Metha Apiwattanakul, MD; Vanda A. Lennon, MD, PhD; Shannon R. Hinson, PhD; Thomas J. Kryzer, AS; Claudia F. Lucchinetti, MD; Brian G. Weinshenker, MD; Dean M. Wingerchuk, MD; Elizabeth A. Shuster, MD; Sean J. Pittock, MD

Arch Neurol. 2009;66(9):1134-1138.

Objective  To compare the sensitivity and specificity of immunofluorescence (IF) and immunoprecipitation (IP) assays using green fluorescent protein–tagged aquaporin-4 (AQP4) in 6335 patients for whom serological evaluation was requested on a service basis.

Design  Case-control study.

Setting  Mayo Clinic Neuroimmunology Laboratory (Rochester, Minnesota) and Departments of Neurology (Rochester, Minnesota; Scottsdale, Arizona; and Jacksonville, Florida).

Patients  Group 1, 835 Mayo Clinic patients, 100 with a neuromyelitis optica (NMO) spectrum disorder diagnosis and 735 without NMO spectrum disorder; group 2, 5500 non–Mayo Clinic patients.

Main Outcome Measure  Sensitivity and specificity of each assay for NMO or NMO spectrum disorder, individually and combined.

Results  In group 1, the sensitivity rates for NMO were IF, 58%; IP, 33%; and combined assays, 63%. The sensitivity rates for relapsing longitudinally extensive transverse myelitis were IF, 29%; IP, 6%; and combined assays, 29%. The specificity rates for NMO and relapsing longitudinally extensive transverse myelitis were IF, 99.6%; IP, 99.3%; and combined assays, 99.2%. In group 2, NMO-IgG was detected by IF in 498 of 5500 patients (9.1%) and by IP in 331 patients (6.0%); 76 of the 331 patients seropositive by IP (23%) were negative by IF. Clinical information was available for 124 patients (including 16 of those seropositive by IP only); 123 had a definite NMO spectrum disorder and 1 was at risk for NMO (monophasic optic neuritis).

Conclusions  In this large, clinical practice-based study, NMO-IgG detected by IF or IP was highly specific for NMO spectrum disorders. The IP assay was significantly less sensitive than IF. Combined testing improved sensitivity by 5%.

Author Affiliations: Departments of Neurology (Drs McKeon, Lennon, Lucchinetti, Weinshenker, and Pittock), Laboratory Medicine and Pathology (Messrs Fryer and Kryzer and Drs Lennon, Apiwattanakul, Hinson, and Pittock), and Immunology (Dr Lennon), Mayo Clinic College of Medicine, Rochester, Minnesota; Department of Neurology, Mayo Clinic, Scottsdale, Arizona (Dr Wingerchuk); and Department of Neurology, Mayo Clinic, Jacksonville, Florida (Dr Shuster).

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