DNA typing and blood transfusion

As the result of a traffic accident, a man was seriously injured. Investigators found him outside the vehicle he had presumably driven. He was taken to the hospital in an unconscious state and there received a number of blood transfusions. Bloodstains found inside the car were collected and sent for comparison with a posttransfusion blood sample of the victim (suspect). As the car involved in the accident had been stolen, the police wished to ascertain whether there was a link between the suspect and the car. Furthermore, being unconscious, the suspect was unable to give a statement. The bloodstains from the car and the blood of the victim were tested by conventional blood group assays and DNA (RFLP and PCR). By conventional blood group assays, the effect of the blood transfusion were seen. On the other hand, the effect of the transfusion were not at all evident in the DNA assays. The implications of these results are discussed. Transfused blood, even in large quantities, did not alter the DNA profile of the recipient in this case.