AIM OSCE / OSPE • MBBS
🔦 Station 7 — Examination of Blood Stains Under Ultraviolet Light
Rapid Revision • Practical Skills • Viva
🎯 Task
You are provided with material bearing a suspected stain and an ultraviolet light source. Demonstrate the correct method of examining the stained area and state the finding that would make you suspect a blood stain.
⚡ Model Station Answer
Technique: I would first inspect the material in ordinary light, wear appropriate eye protection, reduce ambient light and systematically scan the suspected area with the ultraviolet light without touching the specimen.
Finding: Dried blood usually does not fluoresce under UV light. It absorbs light and may therefore remain dark against a fluorescent or lighter surrounding background.
Conclusion: The finding is suggestive of a possible blood stain but is not confirmatory; further forensic testing is required.
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🔎 Stepwise Procedure / Approach
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- Prepare safely. Wear gloves and appropriate UV-protective eyewear before switching on the ultraviolet source.
- Inspect in ordinary light. Observe the material first and note the location, colour, shape and extent of the suspected stain.
- Reduce ambient light. Darken the examination area sufficiently to improve visibility and contrast.
- Position the UV source. Direct the light towards the material without allowing the lamp or your hands to contact the suspected stain.
- Scan systematically. Move the beam slowly across the suspected area and compare it with adjacent unstained material.
- Look for contrast. A dried blood stain usually remains dark or non-fluorescent because blood absorbs the incident light.
- Document the area. Note or photograph the suspected stain and avoid unnecessary handling or contamination.
- Interpret correctly. Report the UV finding as a screening or locating observation and proceed to an appropriate forensic blood test for confirmation.
🖼️ Visual Learning
UV Examination of a Suspected Blood Stain
Technique + Expected Appearance
🎥 Practical Video
This practical demonstration shows the use of forensic alternate-light sources for locating biological evidence and demonstrates the light-absorption principle relevant to blood, alongside fluorescence of other biological materials.
📝 Important Viva Questions
Answer: Blood absorbs certain wavelengths of light rather than characteristically fluorescing, so the stain may appear darker than the surrounding illuminated material.
Answer: Dried blood generally remains dark or non-fluorescent, particularly when the surrounding substrate fluoresces and produces contrast.
Answer: No. UV examination is a screening or locating technique and cannot by itself confirm that the material is blood.
Answer: It improves visualization of fluorescence and absorption contrast between the suspected stain and the surrounding material.
Answer: Appropriate UV-protective eyewear must be worn and the examiner should never look directly into the UV beam.
Answer: Excessive ultraviolet exposure can damage biological material, including DNA, and may compromise subsequent forensic analysis.
Answer: Blood commonly absorbs light and appears dark, whereas some other biological materials may fluoresce. Neither appearance alone is sufficiently specific for definitive identification.