Anti-tissue transglutaminase (tTG) screening using relative light units to identify IgA deficiency.

IgA deficiency is more common in patients with coeliac disease (CD). Total IgA levels are often recommended as part of first line coeliac testing along with anti-tissue transglutaminase (tTG) IgA, to identify these patients and reduce falsely negative results. This study aimed to identify patients with complete IgA deficiency by determining a cut-off threshold on chemiluminescent tTG IgA testing. A chemiluminescent assay QUANTA Flash h-tTG was reviewed using the BIO-FLASH automated platform. tTG relative light units (RLU) were analysed in relation to total IgA levels. Correlation analysis was performed and distributions of tTG RLU were compared between the IgA deficient and IgA detectable groups, and ROC analysis was performed to identify a suitable threshold. A total of 203 samples were reviewed in our initial cohort. There was a strong correlation between IgA and tTG RLU levels (Pearson correlation coefficient 0.495, p<0.001). There was a statistically significant difference of 170.57 RLU between the means of the IgA deficient and IgA detectable group (p<0.001, 156.50-184.64). A receiver operating characteristic (ROC) curve was generated with area under the curve of 0.997. A cut-off of less than 300 tTG RLU for identification of IgA deficiency was chosen, which had a sensitivity and specificity of 100% and 98.9%, respectively. A prospective validation cohort was conducted which confirmed the initial results. Our study has validated an algorithm to identify complete IgA deficiency by implementing a threshold of 300 RLU during tTG IgA testing by chemiluminescent immunoassay. This approach resulted in a sensitivity of 100% to detect patients with complete IgA deficiency. Widespread uptake would result in improved workflow, workload and turnaround time, and reduce the need for unnecessary blanket testing of total IgA in the screening for coeliac disease.