Blood+Outline+JCM

BLOOD OUTLINE

Chemical Methods used to detect blood: -Crystal Test -Catalytic Test -Instrumental Methods Crystal Tests - Based on the formation of haemoglobin derivative crystals such as haematin, haemin and haemochromogen. - The test is carried out on a microscope slide, with the reagents being added to the stain under a cover slip, and crystal formation observed microscopically. - Takayama test (most common) is where an alkaline solution of pyridine is added to the stain and, if blood is present, pink crystals of a complex between pyridine and haem form as the slide is warmed. - Positive results confirms the presence of blood Catalytic Tests - The haem group of haemoglobin possesses a peroxidase-like activity which catalyses the breakdown of hydrogen peroxide - The oxidizing species formed in this reaction can then react with a variety of substrates to produce a visible color change. - Kastle-Meyer Test - These are intended for the detection of blood in urine in clinical situations but are equally useful as a screening test for dried bloodstains. - Extremely sensitive and certain substances can interfere like enzymes. - The general principle is that if the test is negative, blood is absent, but that if the test is positive, blood is probably, not definitely present Instrumental Methods - High performance liquid chromatography (HPLC) can be used to confirm the identity of blood using the absorbance of haemoglobin for detection. This method can also be used to identify the species of origin from variations in the globin chains4, to distinguish foetal haemoglobin from adult haemoglobin5, and to give an estimate of the age of a bloodstain Applications - Use the “Sangur” or Kastle-Meyer Test - “Sangur stick” rubbed gently onto “blood area” moistened and turns from yellow to blue indicates if probable blood stain - Kastle-Meyer Test is kept in alkaline solution in the presence of zinc, the formula is colorless and if it touches blood, it turns to pink Detection of Non Bloodstains - Luminal is sprayed onto suspected area and it turns bluish if there is presence of blood Enhancement of Bloodstains - Luminal and Leucocrystal violet for shoe prints Subsequent reactions of stains treated with blood detecting reagents