Teichmann's Test

Teichmann's test (hemin test) is used for the identification of blood pigments by obtaining characteristic hemin crystals under a microscope, C₃₄H₃₂N₄O₄FeCl (for the structural formula, see Hemoglobin), which can be considered as the chloride ester of hematin. Hemin (hematin hydrochloride) is a blue-black powder in incident light and brown in transmitted light, insoluble in water and other common solvents; it dissolves in hot glacial acetic acid, in acidified alcohol, and also in caustic and carbonate alkalis, changing in the process. To perform Teichmann's test, a drop of blood is placed on a microscope slide and dried very carefully at a temperature not exceeding 60°, then a drop of glacial acetic acid is added, mixed, covered with a coverslip, and heated over a small flame until it begins to boil; when viewed under a microscope, hemin crystals are visible in the form of brown, elongated, rhomboidal plates or needles, often arranged in the form of crosses, stars, or clusters. If crystals do not appear immediately, the heating with glacial acetic acid is repeated. In forensic medical practice, one usually has to deal with suspicious stains on clothing, on suspected murder weapons, etc. Several particles are scraped from the surface of the bloodstain and ground into a powder on a microscope slide, a small crystal of NaCl is added, and then glacial acetic acid (two to three drops) is added, and the procedure is carried out as described above. In cases where the preparation was subjected to heating that was too rapid, incompletely formed crystals resembling hemp seeds are obtained. In polarized light, hemin crystals change their brown color and appear golden-shining in the darkened field of view (pleochroism). Modifications of Teichmann's test proposed by a number of authors are rarely used in forensic medical practice. Only a positive result is significant, since sometimes, despite the undoubted presence of blood in the stain, Teichmann's test does not succeed. According to available observations, the presence of fat, rust, caustic potash, coal, etc., makes it difficult to obtain hemin crystals. Conversely, blood traces that have been subjected to the influence of boiling water and other conditions still yield Teichmann's test. Teichmann's test has sometimes succeeded with bloodstains heated to 140° and even higher, as well as with putrefied and subsequently dried blood. The significant age of the trace does not, in itself, prevent the formation of hemin crystals.