The idea of a detailed antigen-antibody reaction is one that is finding application in other areas unrelated to the blood typing of individuals which can be tested by the use of forensic comparison microscopy. Most importantly, this application has been used in the detection of drugs in live blood and urine samples. Antibodies that are able to react with blood do not usually exists; but then; they can be found in animals such as rabbits by first mixing the drug with the protein and injecting this mixture into the animals. This drug protein complex now acts as antigen stimulating the animal to create antibodies. The recovered live blood serum of the animal will now contain antibodies that are specific or nearly specific toward the drug.
Nowadays, there are a lot of immunological assay technologies commercially available for the detection drugs through an antigen-antibody reaction. One such example of the technique, the enzyme-multiplied immunoassay technique (EMIT), has obtained well-known popularity among toxicologists because of its speed and high sensitivity for finding drugs in urine and they also use forensic comparison microscopy. A typical EMIT analysis starts by adding to a specimen urine antibodies that will bind to the drug being tested. An example of this, if someone’s urine is being checked for the presence of the drug called methadone, the forensic scientist would add methadone antibodies to the urine. If there is any methadone drug present in the urine it will immediately combine with these antibodies. Then enzyme-labeled methadone drug is being added to the urine. So, the methadone antibodies that did not interact with the methadone drug will now combine with the enzyme-labeled methadone. The amount of enzyme-labeled methadone remained uncombined is then measured, and this rate is related to the application of methadone drug that was originally present in the urine.
One of the most frequent uses of the EMIT technique in forensic laboratories (which uses forensic comparison microscopy in all their tests) has been for testing the urine of suspected marijuana smokers. In marijuana, THC is considered the number one pharmacologically active agent. In order to aid its elimination, the body converts THC to a series of substances or metabolites that are more readily removed. The major THC metabolite found in urine is a substance called THC-9-carboxylic acid. It is against this metabolite that antibodies are prepared for testing by the EMIT technique. In general, the urine of marijuana smokers will have THC-9-carboxylic acid in a minute quantity (less than one millionth of a gram); but then, this is a level that is readily detected by the EMIT Testing.
The most common problem connected with marijuana’s detections in urine is interpretation. While smoking marijuana will result in the detection of THC metabolite, it is very difficult to find out with the individual actually used marijuana. In individuals who smoke marijuana regularly, detection is possible within 2 to 5 days after the last use of the drug. But then, some individuals may yield positive results up to 10 days after the last use of marijuana.
Though EMIT is nowadays a popular immunoassay technique in forensic laboratories but then the use of forensic comparison microscope is of the same importance, there are other immunoassay procedures commercially available. For example, radio immunoassay (RIA) uses drugs that are labeled with radioactive tags. Even the forensic analysts are saying that immunoassay techniques are not totally specific for any drug. Other substances have some chemical structure familiar to the drug in question might cross-react with the antibody to give a false positive reaction. Therefore, positive immunoassay tests must always be confirmed by another reliable analytical process, most forensic scientists use forensic comparison microscopy to have an option in this kind of testing. Read more on this subject