Specificity of commercially available antibodies used for gastrin measurement

We examined the specificity of commercially available antibodies used in measurement of serum gastrin. Antibodies were obtained from five commercial laboratories, and antibody immunoreactivity with gastrin and cross-reactivity with cholecystokinin (CCK) were determined. All antibodies were equally immunoreactive with gastrin, and cross-reactivity of three antibodies with CCK was minimal (less than 5%). In contrast, substantial cross-reactivity with CCK was found with two antibodies. To determine the clinical significance of cross-reactivity with CCK, secretin injection tests were performed in 24 individuals: seven in normal health, four with Zollinger-Ellison syndrome, three with antral gastrin cell hyperfunction, six with ordinary duodenal ulcer disease, and four with atrophic gastritis. Serum gastrin levels were measured with all five gastrin antibodies. The response to secretin was negative in all normal subjects and in those with duodenal ulcer and antral gastrin cell hyperfunction. The response to secretin was positive in all four patients with gastrinoma with use of the five antisera. All four patients with atrophic gastritis had normal responses to secretin when antibodies with minimal CCK cross-reactivity were used; however, two of four had false positive secretin test results when serum gastrin levels were measured with the two antibodies with a high degree of cross-reactivity with CCK. These studies indicate that significant cross-reactivity of gastrin antibodies with CCK can result in false positive secretin injection test results and can lead potentially to the erroneous diagnosis of Zollinger-Ellison syndrome.