Cross evaluation of three flow cytometric F cell counting methods performed by different laboratories

Three flow cytometric methods of counting F cells were evaluated in the set tings of an external laboratory assessment scheme. The laboratories to part icipate with a different method were located in Oxford (method O), Athens ( method A) and Jerusalem, (method J). Two monoclonal anti-gamma chain antibo dies were used: monoclonal antibody produced by P. Beverley (Oxford) (BEV) and an antibody provided by Bioatlantic S.A.R.L. (France) (BIO). The specim ens tested were mixtures in five predefined ratios of a sample with homozyg ous GP-thalassemia with 100% F cells with a sample with no P cells. A centr al independent laboratory prepared and distributed the aliquots (at room te mperature) to the participating centers within 2 (O), 3 (A), and 6 (J) days . The performance of the three methods was evaluated by: 1) deviation indic es, 2) relative accuracy, as percent difference of the counts from the targ et values, and 3) bias and linearity by linear regression of the counts ver sus the target values [parameters: slope(s), y-intercept (y), R squared (Rs ), and F ratio]. The highest score of performance was obtained by method A with both monoclonal antibodies.