Question

Subject: Criminal Justice

What role does Hexagon OBTI play when blood evidence has been found?

Answer 1

Hexagon Obti is the perfect complement to the BLUESTAR forensic line of Blood Detection products. This rapid screening test presumes that a bloodstain is of human origin and helps the Investigator to determine whether or not to collect a sample as evidence. A positive result indicates a strong likelihood that the bloodstain is indeed human, and a lab analysis will later confirm or deny that presumption.

Hexagon Obti is a two-part test - 1) a collection tube for the blood sample, 2) a test bar. A sample of the presumed human blood is transferred into the tube with the transport medium. This mixture is then added to the test bar. Typically, a positive reaction will be detected within 2-3 minutes. A single blue line indicates that the testing liquid is working properly, but no human blood has been found. Two blue lines indicate that the test has determined the sample is blood of human origin.

Human hemoglobin (hHb) in the sample will react with the reagent consisting of blue colored particles and monoclonal anti-human Hb antibodies. The immunocomplex migrates to the test zone where it's captured by an immobilized second antibody directed against hHb forming a blue test line which indicates a positive result. Unreactive reagents migrate further and are bound in a second line by immobilized anti-mouse lgC antibodies. This control lindicates proper procedural function and correct handling of the test.

The Hexagon Obti test detects whole blood up to a dilution of 1 : 1,000,000. As few as 500 red cells are required for a positive result.

Function

HEXAGON OBTI has been designed as a rapid immunological test for the qualitative detection of human hemoglobin in stool samples (faecal occult blood). Additionally, the test is suited for forensic purposes to determine whether blood traces are of human/primate origin. HEXAGON OBTI is based on an immunochromatographic technique, featuring immobilised monoclonal antibodies and a coloured particular reagent. Stool samples are taken with a dedicated device which allows a clean and secure sampling. In the sample collection tube haemoglobin is lysed from erythrocytes and preserved for one week at room temperature or in a refrigerator. The test is performed by breaking off the tip of the sample transportation tube and dispensing three full drops onto the sample window of the test device. When the solution migrates along the test device two red lines will appear if hemoglobin is present in concentrations ≥ 0.05 µg/ml. A single red line on the far end of the result window is an indication for a negative result. HEXAGON OBTI consists of individually sealed test cassettes and sample collection tubes

Conclusion:

HEXAGON OBTI shows a sensitivity of at least 30 ng/ml with haemoglobin A and a dynamic measuring range of 0.03 – 2,000 µg/ml. Sickle cell haemoglobin reacts positive, however, the signal is less intense compared to haemoglobin A. Cord blood (that has a higher proportion of haemoglobin F) reacts positive with a reactivity similar to HbA. The test is resistant to the Hook effect up to 10000 µg/ml, where the signal can still be clearly seen.