Iron overdose and detection of gastrointestinal bleeding with the hemoccult and gastroccult assays.

Study Objective: To determine the ability of the Hemoccult and Gastroccult tests (SmithKline Diagnostics) to detect blood in vitro in whole-bowel irrigation (WBI) solution.

Interventions: One tablet of ferrous gluconate 324 mg, ferrous sulfate 325 mg, or ascorbic acid 500 mg; or one Materna prenatal vitamin tablet (Lederle Laboratories) was dissolved in 30 mL of Colyte. Colyte alone and each test solution were tested with Hemoccult and Gastroccult slides, then retested at pH values of 3 and 8. Fresh solutions were then spiked with blood and tested with Gastroccult slides. Materna and ascorbic acid solutions were spiked with blood, then tested with Hemoccult slides.

Results: Positive results were difficult to detect on Gastroccult slides. Hemoccult slides were falsely positive for solutions containing only iron and falsely negative for blood-spiked samples containing ascorbic acid.

Conclusion: Both the Hemoccult and Gastroccult tests may be unreliable in detecting GI bleeding in cases of iron overdose treated with WBI.