Apport du dosage des chaînes légères libres d'immunoglobulines dans le diagnostic et le suivi des gammapathies monoclonales à  chaînes légères

A latex-enhanced assay measuring free light chains (FLC) has recently become available and been reported to be sensitive and specific for detecting FLC diseases. Our aim was to compare this assay applied to 75 patients with FLC monoclonal gammopathies with the conventional techniques. In 100% of cases, quantification of FLC appeared to be informative. At the time of diagnosis, κf/λf ratio demonstrated in all cases the occurrence of a FLC disease. In 90% of cases where a Bence-Jones protein (BJP) was detected, the FLC ratio was abnormal. In 6 cases where the search for a BJP in urine was negative, the FLC ratio was abnormal. κf-alpha-1-antitrypsin complexes and high molecular weight polymeric forms of BJP were shown to explain obvious overestimation of FLC quantitation. In conclusion, we suggest to combine with serum protein electrophoresis the measurement of FLC every time a FLC disease is suspected.