Evidentiary value and effects of contaminants on blood group factors in medico-legal grounds

Background: Blood is considered to be the most common trace evidence obtained from the scene of crime. Blood grouping reveals vital information regarding identification, in relation to crime investigation. With this respect contamination with dust, rust, bacteria and detergent will have any effect on blood grouping was studied. Material and methods: Randomly A, B, AB, Rh positive samples were taken in duplicates and were added with rusted pins, dust particles, detergent, staphylocopcci bacteria and without any addition one tube was kept in room temperature. Controls were kept in refrigerator at 4-8 ˚C to compare the results. Results: There were lots of changes in blood groups after 10 days of incubation in all tubes with contamination. Blood samples in dust after 10 days incubation had changed from A, B, AB to O blood group with Rh negativity. Blood samples in rust had retained with original ABO group but Rh positives were converted to Rh negative. Detergent tubes had also changed Rh positives to negatives retaining original ABO. There was no change in either ABO or Rh blood groups in tubes with Staphylococci bacteria. Conclusion: Stains contaminated with common agents like dust, rust, bacteria and detergent give inconclusive results by mixed agglutination method with passage of time. The results may be accepted with caution, as the opinion might be medico legally significant.