Serum Gastrin

Description of test :    Gastrin is a peptide hormone produced by mucosal G cells of the gastric antrum. It is synthesized as preprogastrin, cleaved toprogastrin, which undergoes several posttranslational modifications,in particular sulfation, and is finally processed into the mature 34amino acid, gastrin-34.Gastrin-34 may be cleaved further into the shorter 17 amino acid, gastrin-17.Either may be secreted as a c-terminal amidated or un-amidated isoform. A number of additional,smaller gastrin fragments, as well as gastrin molecules with atypica posttranslational modifications (eg, absent sulfation), may also be secreted in small quantities.Gastrin half-life is short, 5 minutes for amidated gastrin-17, and 20 to 25 minutes for amidated gastrin- 34.Elimination occurs through peptidase cleavage and renal excretion.

Interpretation :  

1. Achlorhydria is the most common cause of elevated serum gastrin levels.

2. Gastrin levels may be pathologically increased due to hypersecretion by gastrin-producing neuroendocrine tumors, chiefly gastrinomas.25% of which occur as part of the multiple endocrine neoplasia type 1(MEN 1) syndrome and, rarely, foregut carcinoid tumors.

Note :

1. Isolated serum gastrin levels can only be interpreted in fasting patients; nonfasting specimens are uninterpretable.

2. Drugs that interfere with gastric acid secretion, in particular proton pump inhibitors (eg, omeprazole),should be discontinued, if feasible,for at least 1 week before serum gastrin measurement.

3. Drugs that interfere with gastrointestinal motility (eg, opioids) should also be discontinued for at least 5 drug halflives? before serum gastrin testing.

4. There is no evidence that fasting serum gastrin levels differ between adults and children. Although 8-hour fasts are difficult or impossible to enforce in small children, serum gastrin levels after shorter fasting periods(3-8 hours) may be 50-60% higher than the 8-hour fasting value.