An objective measure of stool color for differentiating upper from lower gastrointestinal bleeding

Subjective reporting of the color of blood passed per rectum has been used to predict the location of gastrointestinal bleeding, but the validity of this clinical approach has never been evaluated systematically. In this study we determined the spectrum of patient and physician descriptors used to characterize the color of blood passed per rectum and evaluated prospectively if an objective test of stool color would correlate with or improve upon subjective descriptions in predicting bleeding locations. The objective test employed was a card containing five numbered colors that typify the spectrum of stool blood colors. One hundred twenty patients used 23 different descriptors or terms to verbalize the color of blood they passed per rectum, and in 22% of cases there was a seeming discrepancy between their verbalized color and the color they pointed to on the test card. Patients pointing to card color 4 (the black color) resulted in closer matching to an upper bleeding source than physicians using terminology such as melena or tarry stools. Likewise, patients picking card colors 1 and 2 (the brightest red colors) resulted in closer matching to a coloanorectal bleeding source than physicians using the terms hematochezia or bright red blood per rectum (P < 0.02 for each comparison). The positive predictive value of card color 4 for an upper bleeding source was very high both when patients pointed to this color or when it was determined from the available stool (0.95 and 0.98, respectively). The positive predictive value of card color 1 for lower bleeding was greater for patients selecting this color than for a direct stool comparison (1.00 vs 0.83).