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—We are pleased to learn from Dr Hershey et al that the IgG determinations in their studies were performed by "blinded" technicians, but this was not clear from their original article. As for our use of the upper limit of 0.66 for the IgG index, this was established as the upper limit in our laboratory.After we reviewed the letter of Dr Hershey and colleagues, we reran the statistical analysis on our patients for the IgG index. Since there were so few cases between the 0.5 and 0.9 range, the "false-positive" rate for this measurement for the CSF IgG index was minimally changed. This test remains a very nonspecific one in our laboratory. We certainly agree with Dr Hershey and his colleagues that standardization of both clinical and laboratory criteria is important for future studies.
Caroscio JT, Cohen JA, Yahr MD, Kochwa S, Sacks H. Quantitative CSF IgG Measurements-Reply. Arch Neurol. 1984;41(5):473. doi:10.1001/archneur.1984.04050170015004
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