Failing to Detect Occult Blood

Excerpt

To the editor: In the June 1981 Annals, Layne and associates (1) showed the insensitivity of guaiac slide tests for detecting blood in gastric juice. Subsequent investigators have confirmed the increased rate of false-negative results with Hemoccult II (Smith Kline Diagnostics, Sunnyvale, California) when the pH of the test specimen is below 4 (2-4). Buffering gastric juice with antacid (1), sodium hydroxide (2), or phosphate buffer (3) before its application on the Hemoccult II slide will improve sensitivity, but this is often impractical at the bedside. In 1983, Gastroccult (Smith Kline Diagnostics) was introduced as a guaiac-based slide test specifically