28-P : C1q ASSAY: MAKING SENSE OF SENSITIVITY

Aim The aim is to evaluate in a selected group of patients, the clinical relevance of C1q binding antibodies when compared to those detected by Labscreen®. Methods Class I and II Labscreen® SAB and C1q Screen® were utilized according to manufacturer’s instructions (One Lambda/Fisher, CA). Sera dilutions were also tested utilizing Class I and II Labscreen®. Results We have evaluated 25 samples on the C1q Screen™ and compared them to the Class I and Class II Labscreen® single antigen beads. Sixty percent of all samples continued to be positive on the C1q Screen assay when compared to the Class I and II single antigen Labscreen® assay. However, 40% of the samples are negative on the C1q assay™ when compared to the Labscreen® assay. Since the Labscreen® assay is not a quantitative assay, we were not able to solely attribute the negative result in the C1q Screen™ assay to the lack of complement binding by the antibody. The possibility of a low titer antibody is also possible and could explain the negative results. Therefore, we tested these samples on the Labscreen® assay using 1:4, 1:8 and 1:16 dilutions. All of the samples that tested negative on the C1q Screen™assay were samples that had an antibody titer of 4 or less. Conclusions Our results indicate that most of the samples tested had antibodies that were able to bind complement according to the C1q™ assay. However, 40% of the samples did not show complement binding antibodies. These antibodies that were unable to bind complement had a titer of 4 or less, therefore, rendering a negative result. The C1q Screen™ assay in combination with the Labscreen® assay could help in the clinical decision making as for example which highly sensitized patients will benefit more from desensitization procedures, which antibodies to avoid at transplant or which post- transplant patients will need an immediate pharmacological intervention.