Gastric parietal cell antibody detection by kidney/stomach IFA and H+/K+ ATPase ELISA procedures

Abstract

Objective: Evaluate the performance of a new ELISA kit for the detection of anti-gastric parietal cell antibodies in normal and clinically-defined specimens. Compare ELISA results obtained with conventional testing using indirect immunofluorescence (IFA) on rodent kidney/stomach-slides.Methods: Specimens from patients with pernicious anemia, various autoimmune or infectious disease conditions, healthy individuals, and specimens submitted to a reference laboratory for gastric parietal cell antibody testing were collected. Specimens were tested by the INOVA QUANTA Lite™ Gastric parietal antibody (GPA) ELISA, which utilizes purified H+/K+ ATPase antigen as the substrate, and by IFA on rodent kidney/stomach-slides.Results: Testing of 210 specimens from normal, healthy individuals with ages ranging from 17 to 77 years old, resulted in a specificity of 96.6% (199/206). Of the 7 GPA positive specimens, the 2 specimens with the highest values were found to be GPA IFA positive.Antibodies to gastric parietal cells have been reported in up to 90% of patients with pernicious anemia. Testing a panel of blinded specimens from 20 patients with pernicious anemia resulted in 15 of the 20 interpreted as positive by the GPA ELISA. IFA test results performed at INOVA were in complete agreement with the GPA ELISA results, while results at the Italian site interpreted 18 specimens 1+ or 2+ and 2 specimens as weakly reactive by IFA. Several of the GPA ELISA negative pernicious anemia specimens were positive for intrinsic factor antibodies by a prototype intrinsic factor ELISA kit and suggest the value of testing for both GPA and intrinsic factor antibodies. Additional testing of a panel of specimens submitted to various laboratories for GPA testing found a 92% (45/49) agreement between the GPA ELISA and IFA assays.Sera from 49 patients with autoimmune, infectious, or other clinical conditions were tested on the GPA ELISA. Three specimens were positive for GPA antibodies and subsequently found to be positive for GPA by IFA. While the results of IFA testing generally agreed between laboratories, a few samples were consistently interpreted differently in different laboratories.Conclusion: The QUANTA Lite™ GPA ELISA allows the sensitive and specific detection of gastric parietal antibodies in human sera using a defined target antigen, H+/K+ ATPase. In contrast to the conventional GPA IFA procedure, the assay is not dependent on subjective interpretation and allows more objective, reproducible, and automatable testing for GPA.