The UK National External Quality Assessment Scheme in Blood Group Serology. ABO and D grouping, antibody screening, direct antiglobulin test and antibody identification 1984-1985.

In seven exercises of blood grouping the overall rates of major error were 0.19% and 0.25% in ABO and D grouping respectively. In ABO grouping this represents an increase in error rate over that observed in 1982-1983 but the increase was due to an unusually high error rate with one particular group A2B cell. An improvement in performance was observed in simple D grouping and was largely due to a lower incidence of false positive grouping of D-negative cells in the antiglobulin test. An improvement in performance observed in D grouping IgG-coated D-negative cells appeared to be due to a better understanding of the problem rather than to any change in serological practice. Error rates in antibody screening were somewhat lower than in 1982-1983 but this may or may not represent an improvement in performance as the test materials were not the same in the two periods. The direct antiglobulin test with IgG-coated cells was reliably performed with polyspecific and with anti-IgG reagents but an excess of false positive results was obtained with anti-C3d. Error rates in antibody identification varied from 0.6% for anti-D to 74% for anti-c + E.