Which test determines whether blood is of human or animal origin?

Which test determines whether blood is of human or animal origin?

• A. Precipitin test.
• B. Kastle-Meyer test.
• C. Luminol.
• D. PSA test.

Answer: (A)

The key idea is identifying the species of origin for blood using an immune-based reaction. The precipitin test uses antibodies raised against human serum. When a blood sample containing human proteins is exposed to this anti-human serum, the antibodies bind the human antigens and form an insoluble precipitate, visible as a line or zone of precipitation. If the blood is from an animal, the anti-human serum won’t bind, so no precipitin line appears. This direct antigen–antibody reaction is what makes the test capable of distinguishing human blood from animal blood. The other methods don’t determine origin in this way. Kastle-Meyer is a presumptive color test for the presence of blood, not its species. Luminol detects latent blood by chemiluminescence but doesn’t identify species. The PSA test is used to detect semen (human seminal fluid) and isn’t a general test to tell whether blood is human versus animal.

The key idea is identifying the species of origin for blood using an immune-based reaction. The precipitin test uses antibodies raised against human serum. When a blood sample containing human proteins is exposed to this anti-human serum, the antibodies bind the human antigens and form an insoluble precipitate, visible as a line or zone of precipitation. If the blood is from an animal, the anti-human serum won’t bind, so no precipitin line appears. This direct antigen–antibody reaction is what makes the test capable of distinguishing human blood from animal blood.

The other methods don’t determine origin in this way. Kastle-Meyer is a presumptive color test for the presence of blood, not its species. Luminol detects latent blood by chemiluminescence but doesn’t identify species. The PSA test is used to detect semen (human seminal fluid) and isn’t a general test to tell whether blood is human versus animal.