Validation of Dried Blood Spot Immunoreactive Trypsinogen (DBS-IRT) as a Biomarker of Exocrine Pancreas Function in Children with Pancreas Disease

Introduction: Radioimmunoassay (RIA)-serum trypsin serves as pancreas function biomarker as its blood concentration correlates with duodenal trypsin output. With the unavailability of RIA tests and global availability of dried blood spot immunoreactive trypsin (DBS-IRT) testing as part of cystic fibrosis (CF) newborn-screening programs, IRT can be made accessible for routine clinical use. We aimed to validate DBS-IRT for its use as a biomarker of exocrine pancreas function in children beyond the newborn age group. Methods: Analytical accuracy of DBS-IRT was evaluated in 28 children [mean(SD) age:13(4.5) years] with known pancreas function status and simultaneous serum RIA-trypsin testing. Reference ranges were established based on 134 metabolically stable children. Clinical validation was performed in 164 children with well-established pancreas phenotypes. Available cross-sectional imaging was reviewed to assess for pancreas atrophy as a means to measure acinar cell loss. Results: Total imprecision of DBS-IRT ranged from 7.1-16.4%, samples were stable samples at -20 0 C for 28-days and showed excellent correlation to serum RIA-trypsin (r=0.95, p<0.001). A reference range of 6.9 to 21.2ng/mL was newly established. DBS-IRT replicated serum trypsin in discriminating exocrine pancreatic insufficiency (EPI) in the CF group with high sensitivity (90.7%;95%CI:79.7-96.9%) and specificity (94.7%;95%CI:73.9-99.8%). Children with pancreatitis and EPI had significantly lower median DBS-IRT level compared to those without EPI (p=0.01). Low DBS-IRT was associated with pancreas atrophy (p=0.001). Conclusions: DBS-IRT was successfully validated as a biomarker of exocrine pancreas function which allows its use in clinical setting, in addition to fecal elastase to determine pancreas function.