External quality control in blood transfusion serology: results from the Finnish proficiency testing programme in...

Results from the Finnish interlaboratory proficiency testing programme in immunohaematology from 1976 to 1978 are reviewed. The results show excellent accuracy of ABO grouping (100% correct). In Rh (D) grouping the detection of weak D antigen (Du) offered difficulties due to insufficient methodology. Also a sample from a donor with a positive direct antiglobulin reaction created confusion in Rh (D) grouping. The screening of atypical antibodies in serum was performed excellently (100% correct); the antibody coating of red cells, however, was detected by only 83.3% of the participants. The accuracy of compatible crossmatches was good (on average 98.7% correct); the accuracy of incompatible crossmatches, however, was poorer (on average 88.1% correct). A considerable methodological variation in compatibility testing is suggested to be responsible for the poor performance. The performance of individual laboratories seemed to correlate with their position in the health service organization, and with the level of internal quality control procedures.