A potential error in the quantitation of fecal blood loss: Concise communication

Chromium 51 labeled red cells were used to quantitate fecal blood loss in a patient with chronic upper gastrointestinal hemorrhage. On day 1, the stool guaiac was positive but the blood loss indicated by ⁵¹Cr was less than 1 cm ³. Blood loss in the stool by ⁵¹Cr did not become significant until day 3, when it measured 23 cm ³. The failure to detect abnormal blood loss on day 1, and probably on day 2, appears to be due to a long intestinal transit time from a proximal bleeding site. The problem of slow intestinal transit is not uncommon and could lead to a false negative study or falsely low estimates of fecal blood loss. This problem could be minimized by beginning stool collection on day 3 or by delaying stool collection until the appearance in the stool of an oral nonabsorbable marker swallowed when the ⁵¹Cr tagged red cells are injected.