False-positive serum gastrin elevation during secretin stimulation due to Boots secretin

Five patients with hypochlorhydria, chronic gastritis, and high serum gastrin levels and four control subjects underwent secretin stimulation testing. Gastrin determinations were made by a commercially available radioimmunoassay kit. Intravenous Boots secretin gave positive stimulation tests in all patients and controls. Positive Boots secretin stimulation tests in two of the control subjects were confirmed by a different gastrin assay kit. Synthetic secretin stimulation in two of the patients and the four control subjects showed no rise in postsecretin gastrin. Gastrin assay of pure Boots secretin from three different lots gave values ranging from 170,000 to 1,620,000 pg/ml. Gastrin assay of synthetic CCK 8 gave values of 718,600 and 1,300,000 pg/ml. Gastrin-like activity was undetectable in synthetic and GIH secretin and the normal saline used as a diluent. We conclude: 1) Boots secretin contains a contaminating substance or substances exhibiting immunoreactivity with commercially available gastrin assay kits, 2) cholecystokinin or cholecystokinin-like peptides are the leading candidates for contaminating substances in some assays, and 3) Boots secretin can cause false-positive secretin stimulation tests and should not be used in the secretin stimulation test for hypergastrinemia. We have switched exclusively to Kabi (GIH) secretin.