MODEL RELEASED. Forensic blood test. Image 2 of 5. Forensics officer performing a blood verification test on a stain on the sole of a shoe. During the test, a swab is treated with chemicals and then wiped over the stain. If the stain is blood, the chemicals react and the swab changes colour. The test being used is the Kastle- Meyer Presumptive blood test. If blood is found on the shoes, its DNA can be extracted and analysed and may provide evidence in a criminal investigation. For a sequence of images of the test, see H200/621 to H200/625.