Investigation into low-level anti-rubella virus IgG results reported by commercial immunoassays.

Since the 1980s, commercial anti-rubella virus IgG assays have been calibrated against a WHO International Standard and results have been reported in international units per milliliter (IU/ml). Laboratories testing routine patients' samples collected 100 samples that gave anti-rubella virus IgG results of 40 IU/ml or less from each of five different commercial immunoassays (CIA). The total of 500 quantitative results obtained from 100 samples from each CIA were compared with results obtained from an in-house enzyme immunoassay (IH-EIA) calibrated using the WHO standard.