Confirmatory Tests for Blood
Forensic Serology: Establishing Human Identity
In forensic science, blood evidence must first undergo presumptive tests (which indicate the presence of blood, e.g., Kastle-Meyer, Benzidine, Hemastix) followed by confirmatory tests to definitively prove it is blood.
1. Microcrystalline Tests
These tests rely on the formation of characteristic crystals when blood-specific pigments (like hemin) react with chemical reagents.
| Test | Reaction/Crystal Characteristic |
|---|---|
| Teichmann Test | Forms brown, rhombic crystals of Hemin (hematin chloride). |
| Takayama Test | Forms pink, feathery crystals of Pyridine Hemochromogen. (More sensitive than Teichmann). |
2. Spectroscopic and Immunological Methods
- Absorption Spectroscopy: Examines the absorption spectrum of hemoglobin derivatives (e.g., oxyhemoglobin, carboxyhemoglobin).
- Precipitin Test: An immunological test used to determine the species origin of the blood (Human vs. Animal) by detecting serum proteins.
- High-Performance Liquid Chromatography (HPLC): Often used in modern laboratories for definitive confirmation.
3. Forensic High-Yield Pearls
- Sensitivity vs. Specificity: Presumptive tests are highly sensitive but prone to false positives (e.g., peroxidase-like activity in vegetables). Confirmatory tests are specifically designed to eliminate these false positives.
- Limitations: Old, dried, or heated stains can sometimes result in false negatives for crystal tests due to the denaturation of hemoglobin.
- Educational Resource: For more detailed forensic serology protocols and practice questions, please visit mymedschool.org.