Detection of rubella immunoglobulin M from dried venous blood spots using a commercial enzyme immunoassay.

Confirmation of the diagnosis is critical to disease control in measles elimination and rubella control programs. In countries with limited infrastructure and laboratory capacity, collection, transport, and testing of venous blood samples may be difficult. We report the adaptation of a commercial enzyme immunoassay for the detection of rubella immunoglobulin M (IgM) in dried venous blood (DVB). We used 60 DVB, prepared at the time of venous blood collection, from the enhanced measles/rubella surveillance program and 28 DVB prepared using donor red blood cells spiked with serum, which had been tested as part of a rubella outbreak. Adaptations of the manufacturer's protocol included variations in incubation times and washing procedures. Optical densities were corrected for kit variation as recommended by the manufacturer, but no further adjustment was needed to compare serum and DVB results. Counting equivocal results as positive, the sensitivity of the DVB compared with serum for the categorization of rubella IgM as positive or negative was 96.7% (95% confidence interval [CI], 83.3-100%) and the specificity was 100% (95% CI, 93.7-100%).