Traque des interférences en immunoanalyse : la coopération entre le laboratoire et le fabricant est indispensable. L'exemple de la T3 libre Elecsys®

Interference from heterophilic antibodies, generally suspected by clinicians faced with discrepant clinical and biological data, remains a problem as regards immunoassays. In the laboratory, we checked for interference in a FT3 assay by studying associations between increased Elecsys FT3 values and normal Elecsys TSH results. Out of 10,000 sera analysed between May 2004 and October 2005 we found 38 such cases. In 14 out of these 38 sera, the increased Elecsys FT3 level was confirmed by a two-step radioimmunoassay, but in the remaining 24 sera interference was suspected. Screenings for anti-T3 or heterophilic antibodies and for drug interference were unsuccessful. Out of these 24 sera, 16 were sent to the manufacturer's laboratory for further investigations. Interference from anti-idiotype antibodies was evidenced in 3 sera and interference from anti-ruthenium antibodies in the other 13 samples. The manufacturer developed a reagent to eliminate interference due to anti-ruthenium antibodies. Interference due to anti-idiotype antibodies remains difficult to eliminate. In this study its frequency (around 0.03%) is in accordance with the state-of-the-art (< 0.05%) in immunoassays incorporating unspecific and specific interference blocking reagents.