How accurate are drug tests?
What do these tests do? These tests indicate if one or more prescription or illegal drugs are present in urine. These tests detect the presence of drugs such as marijuana, cocaine, opiates, methamphetamine, amphetamines, PCP, benzodiazepine, barbiturates, methadone, tricyclic antidepressants, ecstasy, and oxycodone.
The testing is done in two steps. First, you do a quick at-home test. Second, if the test suggests that drugs may be present, you send the sample to a laboratory for additional testing.
What are drugs of abuse? Drugs of abuse are illegal or prescription medicines (for example, Oxycodone or Valium) that are taken for a non-medical purpose. Non-medical purposes for a prescription drug include taking the medication for longer than your doctor prescribed it for or for a purpose other than what the doctor prescribed it for. Medications are not drugs of abuse if they are taken according to your doctor’s instructions.
What type of test are these? They are qualitative tests -- you find out if a particular drug may be in the urine, but not how much is present.
When should you do these tests? You should use these tests when you think someone might be abusing prescription or illegal drugs. If you are worried about a specific drug, make sure to check the label to confirm that this test is designed to detect the drug you are looking for.
How accurate are these tests? The at-home testing part of this test is fairly sensitive to the presence of drugs in the urine. This means that if drugs are present, you will usually get a preliminary (or presumptive) positive test result. If you get a preliminary positive result, you should send the urine sample to the laboratory for a second test.
It is very important to send the urine sample to the laboratory to confirm a positive at-home result because certain foods, food supplements, beverages, or medicines can affect the results of at-home tests. Laboratory tests are the most reliable way to confirm drugs of abuse.
Many things can affect the accuracy of these tests, including (but not limited to):
- the way you did the test
- the way you stored the test or urine
- what the person ate or drank before taking the test
- any other prescription or over-the-counter drugs the person may have taken before the test
Note that a result showing the presence of an amphetamine should be considered carefully, even when this result is confirmed in the laboratory testing. Some over-the-counter medications will produce the same test results as illegally-abused amphetamines.
Does a positive test mean that you found drugs of abuse? No. Take no serious actions until you get the laboratory's result. Remember that many factors may cause a false positive result in the home test.
Remember that a positive test for a prescription drug does not mean that a person is abusing the drug, because there is no way for the test to indicate acceptable levels compared to abusive levels of prescribed drugs.
If the test results are negative, can you be sure that the person you tested did not abuse drugs? No. No drug test of this type is 100% accurate. There are several factors that can make the test results negative even though the person is abusing drugs. First, you may have tested for the wrong drugs. Or, you may not have tested the urine when it contained drugs. It takes time for drugs to appear in the urine after a person takes them, and they do not stay in the urine indefinitely; you may have collected the urine too late or too soon. It is also possible that the chemicals in the test went bad because they were stored incorrectly or they passed their expiration date.
If you get a negative test result, but still suspect that someone is abusing drugs, you can test again at a later time. Talk to your doctor if you need more help deciding what steps to take next.
How soon after a person takes drugs, will they show up in a drug test? And how long after a person takes drugs, will they continue to show up in a drug test? The drug clearance rate tells how soon a person may have a positive test after taking a particular drug. It also tells how long the person may continue to test positive after the last time he or she took the drug. Clearance rates for common drugs of abuse are given below. These are only guidelines, however, and the times can vary significantly from these estimates based on how long the person has been taking the drug, the amount of drug they use, or the person's metabolism.
|Drug||How soon after taking drug will there be a positive drug test?||How long after taking drug will there continue to be a positive drug test?|
|Marijuana/Pot||1-3 hours||1-7 days|
|Crack (Cocaine)||2-6 hours||2-3 days|
|Heroin (Opiates)||2-6 hours||1-3 days|
|4-6 hours||2-3 days|
|Angel Dust/PCP||4-6 hours||7-14 days|
|Ecstasy||2 to 7 hours||2 - 4 days|
|Benzodiazepine||2 -7 hours||1 - 4 days|
|Barbiturates||2 - 4 hours||1 - 3 weeks|
|Methadone||3 - 8 hours||1 - 3 days|
|Tricyclic Antidepressants||8 - 12 hours||2 - 7 days|
|Oxycodone||1 - 3 hours||1 - 2 days|
How do you do a drugs of abuse test?
These tests usually contain a sample collection cup, the drug test (it may be test strips, a test card, a test cassette, or other method for testing the urine), and an instruction leaflet or booklet. It is very important that the person doing the test reads and understands the instructions first, before even collecting the sample. This is important because with most test kits, the result must be visually read within a certain number of minutes after the test is started.
You collect urine in the sample collection cup and test it according to the instructions. If the test indicates the preliminary presence of one or more drugs, the sample should be sent to a laboratory where a more specific chemical test will be used order to obtain a final result. Some home use kits have a shipping container and pre-addressed mailer in them. If you have questions about using these tests, or the results that you are getting, you should contact your healthcare provider.