Fun Times: Testing for Blood, Semen, and Urine


Television and film has ruined humans. Totally destroyed them. Hollywood turned what used to be upright-walking mammals with keen minds into people who believe cops can look at a bullet wound and immediately know what the shooter had for breakfast last Thursday. TV has turned our brains into boiling and roiling and festering soups of forensic mush.

Please, allow me to explain… Cops don’t taste suspected drugs. CSI folks do not rappel from skyscrapers to chase down a suspected serial killer (they collect evidence, not create it by falling 80 stories to the pavement below). And no, writers should never, ever use TV as a catchall research source. NOT EVER.

I know, TV portrays the job of CSI’s and forensic scientists as extremely glamorous and exciting. They show these characters driving cool cars and conducting fancy tests in darkened rooms, producing instant “aha” moments that lead to the immediate arrest of the dreaded three-headed-destroy-the-world boogeyman du jour.

Well, the reality is…and this is between us…that’s NOT reality. In fact, forensic scientists work in brightly lit labs and offices where they do this…


Laboratory Testing of Suspected Blood Sample

  1. Moisten a cotton swab with distilled water and use it to gently rub suspected stain.
  2. Add one drop of ethanol.
  3. Add one drop of 1:5 dilution of phenolphthalein.
  4. Add one drop of 3% hydrogen peroxide.
  5. Note any color change. An immediate pink color is expected if blood is present.
  6. Add one drop of tetramethylbenzidine stock solution.
  7. Note any color change. An immediate blue-green color is expected if blood is present.

Time to interpret the results:

Positive for blood = Immediate pink color at step 5 followed by an immediate bluish-green color at step 7.

Negative results = no color change at steps 5 and 7.

Inconclusive = any results other than the above.

Laboratory Testing for Blood Using Luminol and/or BlueStar


  1. In darkened conditions, spray suspected bloodstain with Luminol or Bluestar
  2. Areas containing blood will luminesce immediately. If not, the test result is negative. Weak luminescence is an inconclusive result that could be caused by the chemical contacting  copper, some bleaches and paints, plant matter (carrots for one) and even horseradish, all of which cause a reaction when exposed to luminal or BlueStar.



A common misconception that’s often found in books and on TV and film is that toxicology tests return results for every known chemical, poison, and drug known to man. Not so. Testing is specific. For example, here are the more commonly “tested for” drugs based on a predetermined panel. Anything else is extra and must be specified. Otherwise it will remain as unknown. (Panels may vary depending upon laboratory policy).

Postmortem Tox Panel

Barbiturates Benzodiazepines Carisoprodol
Cocaine metabolite Fentanyl
Methadone Methamphetamine/MDMA






Extra Panel

Acetylsalicylic acid (salicylate)

Analytes run individually by request


Fun Forensics Facts

  1. Prior to testing material for the presence of semen, spermatozoa  must be extracted from the substrate. The process involves a spatula, a bit of teasing and soaking, a pair of tweezers, and a dissecting needle. You are free to use your imaginations.
  2. Tools used in the lab to detect the presence of urine – tweezers, litmus paper, scissors, a scalpel, and some corks. Again, let your imaginations take it from here.