Guaiac Test

Guaiac Test, Almen and van-Deen test, for the detection of blood pigments in feces, gastric contents, etc. It is used in Weber's modification: the feces is triturated with water (2 parts by volume) and glacial acetic acid (1 part) to convert hemoglobin into acid hematin, and then the mixture is extracted with a small amount of ether. After standing, the ether extract is aspirated, 10 drops of fresh alcoholic tincture of guaiac resin and 20 drops of old turpentine that has been exposed to air or 3% hydrogen peroxide are added to it. In the presence of blood pigment, the extract turns blue-violet; in its absence, a brownish-red or greenish coloration is obtained. For clarity, the coloring pigment can be extracted with chloroform, after adding a little water to the test tube. To conduct the examination, the patient must be kept on a milk-vegetable diet for several days, as blood pigments in food can simulate gastrointestinal bleeding. The sensitivity of the test is low, which is why in recent times it is used less frequently and is replaced by tests with benzidine (see) and pyramidone.