Hexagon OBTI is a simple two-part test that can verify if a bloodstain is specifically human blood. First, collect a sample of the presumed human blood trace and place in the included collection tube and transport medium. This mixture is then added drop by drop to the test strip. A positive sample is typically detected within 2-3 minutes. A single blue line means the testing liquid is working fine but no human blood has been detected. Two blue lines mean the test has detected human blood. The test detects whole blood up to a dilution of 1:1,000,000. As little as 500 red cells are required for a positive result. Each box includes 24 collection tubes and 24 tests.