Occult Faecal Blood Loss Determined by Chemical Tests and a ⁵¹Cr Method

Abstract

Stools from volunteers participating in an acetylsalicylic acid (ASA) study were examined during periods with restrictive and liberal diets. With ⁵¹Cr-determined faecal blood less than 2 ml/100 g, the rates of positive benzidine and 3, 3′,5,5′-tetra-methylbenzidine (TMB) tests were about 5% and 25% for periods with restrictive and liberal diets, respectively. Similarly, Fecatest® showed 2% positive tests on a restrictive and 8% on a liberal diet, whereas Hemoccult® II slide and BM-test-Hemafecia showed less than 5% positive tests on both diets. When ASA-induced blood loss (mainly gastric) exceeded 5 ml/100 g faeces, the rate of positive benzidine and TMB tests, including the Hemo-Fec® Test, varied from 87% to 100%. Fecatest detected half of these cases, whereas Hemoccult II and BM-test-Hemafecia were positive in less than one third. By repeated analyses of faecal specimens stored for 3 days, Fecatest showed a substantially increased sensitivity. We assume that benzidine and TMB tests are sensitive enough to detect occult blood loss from all levels of the gastrointestinal tract, but dietary restrictions are essential to reduce the rate of false-positive tests. Guaiac tests, perhaps with the exception of Fecatest, should be reserved for the detection of occult blood loss from the lower gastrointestinal tract.

Key-words:

• Benzidine, analysis
• blood, analysis
• chromium radioisotope
• faeces, analysis
• guaiac, analysis
• tetramethylbenzidine, analysis