Diagnostic accuracy of an agarose gel electrophoretic method in multiple sclerosis.
To the Editor: In .95% of patients suffering from clinically unambiguous multiple sclerosis (MS), oligoclonal IgG can be detected in cerebrospinal fluid (CSF) (1, 2). Isoelectric focusing is the most sensitive method for detecting oligoclonal bands (OCBs) (1 ), whereas agarose gel electrophoresis is reported to detect OCBs in ;80% of cases (2 ). A commercial electrophoresis unit (Beckman Instruments) is commonly used in clinical laboratories. Laboratory support of a clinically probable diagnosis of MS in combination with brain magnetic resonance imaging is important to allow initiation of appropriate treatment as early as possible. We evaluated the sensitivity of the Beckman modified agarose gel electrophoresis to detect OCB and estimated its diagnostic accuracy. We examined paired CSF and sera from 168 patients (122 females) with clinically unambiguous MS (3 ) for the presence of oligoclonal IgG. We followed the manufacturer’s instructions for application of samples to the buffered agarose gel (SPEII gel). Electrophoresis was performed at 100 V for 40 min, followed by immobilization in a fixative solution and staining. All tests were done by the same technician and evaluated by the same experienced hematologist, both unaware of clinical or magnetic resonance imaging data. OCB was detectable in 90 of the 168 patients (53%; 95% confidence interval, 52.9–53.1%). The mean IgG index [(CSF-IgG/serum-IgG)/(CSFalbumin/serum-albumin)] of OCBnegative patients was 0.87. Patients with detectable OCB had a mean IgG index of 1.28 (reference value ,0.7). This electrophoretic method does not appear to provide adequate clinical sensitivity because false-negative results in the detection of OCB may delay diagnosis and the start of treatment.