Gregersen Test

Gregersen Test (Gregersen), a modification of the benzidine test for occult blood in feces. 0.025 g of benzidine and 0.1 g of barium peroxide are dissolved in 5 cm³ of 50% acetic acid. Several drops of the solution are applied to a smear of feces ground on a slide. In the presence of blood, a greenish-blue to dark blue coloration appears. The coloration appears after several seconds, usually not later than two minutes. The reagents must be used fresh. The patient must be kept on a milk-vegetable diet for several days beforehand. The reaction is conclusive for bleeding from the esophagus, stomach, or intestines, if the possibility of blood admixture from the oral cavity and nasopharynx is excluded. Advantages of the test over the benzidine test: greater stability of barium peroxide compared to H₂O₂ and reduced excessive sensitivity of benzidine.