Title:A comparison of positivity using routine incubation, extended incubation and antihuman globulin in the Complement Dependent Cytotoxicity (CDC) assay

Author:MP Chacko, R Shanthi, D Dolly.

Abstract:Objectives: This study quantified and compared positivity obtained on complement dependent cytotoxicity (CDC) using routine incubation, extended incubation and anti-human globulin.
Methods: This was a retrospective study which included results from all samples processed for CDC as part of pretransplant screening in our laboratory in 2013. Samples were processed in parallel for routine incubation CDC, extended incubation CDC and anti-human globulin CDC techniques. Positivity in terms of percentage dead cells was recorded for each technique. All samples that showed positive results (>/=10% dead cells) by at least one method were included in statistical analysis to compare degree of positivity. Negative samples and those that failed validation controls by any technique were excluded. Results of extended incubation CDC were analysed in 131 samples, routine incubation CDC in 103 and anti-human globulin CDC in 111. Results were recorded as percentage dead cells and these values were compared between techniques using the paired t test.
Results: Comparison of reactivity of extended incubation CDC and anti-human globulin CDC with routine incubation CDC, showed a highly significant difference (p<0.0001 and 0.003 respectively) with a mean increase in positivity of 7% over routine incubation with both extended incubation CDC and anti-human globulin CDC. Comparison of extended incubation CDC to the anti-human globulin CDC showed no significant difference p=0.19). Routine incubation missed positivity in 30% of the positive samples tested.
Conclusions: Anti-human globulin and extended incubation enhance the positivity of CDC by approximately 7%. However, neither anti-human globulin CDC nor extended incubation CDC showed any significant increase in positivity over each other.
Key words: anti-human globulin, complement dependent cytotoxicity, crossmatch, extended incubation, human leukocyte antigens.
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