Spontaneous agglutination of red cells with a positive direct antiglobulin test in various media

Abstract
Red cells from 475 individuals (donors and patients) with a positive direct antiglobulin test (DAT) (66% were 1/2+ to 1+, 19% were 1 1/2+ to 2+, and 15% were 2 1/2+ or greater) were examined for spontaneous agglutination following incubation in various media. Of the samples 23% showed spontaneous agglutination in commercial Rh control solutions, 6% in 30% albumin, 3% in 10% albumin, 2% in 6% albumin, and 1% in saline. Cells suspended in serum were more prone to spontaneous agglutination. The strength of spontaneous agglutination varied: more than 50% of the samples reacted only 1+ or less; .apprx. 10% reacted 2+ or stronger. There was not a complete correlation with spontaneous agglutination and quantity of IgG on the cells, as determined by the antiglobulin test. Of those samples showing spontaneous agglutination, 50% were associated with a DAT strength of more than 2+, 27% with a DAT of 1 1/2+ to 2+, and 23% with a DAT of 1/2+ to 1+. Spontaneous agglutination occurred with the same frequency whether the cells were sensitized with both IgG and C3 or with IgG alone. Surprisingly, 7% of the samples sensitized with C3 but no detectable IgG also demonstrated spontaneous agglutination. Marked differences in reaction strength were seen with Rh control solutions from different manufacturers, and the degree of spontaneous agglutination was incosistent with individual products.

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