Increased sensitivity of the card agglutination test CATT/Trypanosoma brucei gambiense by inhibition of complement

CATT/Trypanosoma brucei (T.b.) gambiense is an antibody detection test currently used in field surveys on Gambian sleeping sickness. The screening test is usually performed on a drop of freshly collected heparinized blood, followed by a more specific confirmation test on diluted blood, plasma or serum. This approach may be biased by the occurrence of a complement-mediated prozone phenomenon causing lower test sensitivity at lower sample dilutions. A simple remedy is by addition of a Ca2+ chelating agent such as EDTA.