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There are many different ways that doctors can check for drugs in the body. Drugs show up in the urine, hair, blood, etc. Prescription medications show up in a drug test the same way that illegal drugs show up. Urinalysis is the most common drug test that is used. Say for example a person is taking Vicodin for pain and they have a doctors prescription for it. This will show up on a urinalysis but this person would pass the test because the drug was ordered by a doctor. Here is another example. A person is taking Vicodin but because they have an addiction to it and they are purchasing it illegally. They would fail the drug test because they have no doctors order for the drug. Prior to taking a urinalysis, you will be asked if you are on any prescription medications. You may also be asked to show proof that these drugs have in fact been ordered by a physician. A drug is a drug whether it is a prescription drug or an illegal drug.
Literally hundreds of medications can change or alter the results of a urinalysis (UA). Many change the physical characteristics, others change the chemical characteristics. A very partial list would be:
1. Deferoxamine turns the urine red.
2. Nitrofurantoin turns the urine brown.
3. Many vitamins change the odor of urine.
4. Diazoxide decreases the pH.
5. Tolmetin will cause a false positive for proteinuria.
6. Bacitracin causes a true proteinuria (protein in the urine).
7. Tetracycline causes a false positive for glycosuria (glucose in the urine).
8. Methicillin causes a leukocytosis (white blood cells in the urine).
9. Sulfonamides can cause a hematuria (blood in the urine).
10. Isoniazid causes ketonuria (ketone bodies in the urine).
11. Furosemide causes casts in the urine.
12. Theophyline causes crystals in the urine.
Many more examples exist. This is a good example of why health care providers should familiarize themselves with commonly prescribed medications and the potential changes they can have on laboratory data. An abnormality noted on lab work may not be a true abnormality.
Diagnostics/Springhouse/p. 356, 357
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