Understanding False Positive and False Negative Results
What is a false positive for drug tests? A false positive is a positive test result when the person actually should have a negative result. It can happen when a medication cross-reacts with the immunoassay. This is due to a similar structure in common substances.
Over-the-counter medications, other prescribed medications, and certain foods can cause a false positive.
What are some common reasons for a false positive due to cross-reaction?
- Natural Herbal Supplements and Vitamin Supplements– Among the most notable are Vitamin B supplements; these can give a false positive for THC.
- Ibuprofen –this over-the-counter pain reliever could also give false positive results for benzodiazepines and barbiturates.
- Cold Medicines – Many over-the-counter cold remedies contain synthetic amphetamines, more commonly known as pseudoephedrine, which are also used to produce methamphetamines, a class of illegal drugs.
What is a false negative result? A false negative is a negative test result when a person actually should have a positive result.
Why do false negatives occur? Diluted urine can cause a false negative because the urine drug concentration is below the threshold or cutoff level. A person may also receive a false negative depending on the length of time between the substance use and testing for the substance, as well as the actual amount of the substance used. (Reworded a bit.)
Opiates can be a risk for false negatives because the metabolite may not be as easily detected. Morphine panels with a higher, more sensitive cutoff of 300 ng/mL may be a better option if you are at a higher risk for a positive for opiates.
For any pre-employment drug testing, it is in one’s best interest to provide a detailed list of items that could alter test results, including:
- over-the-counter medications and pain relievers
- cold remedies
- vitamin supplements
- herbal supplements
- nutritional supplements
- prescription medications
- foods and beverages consumed up to 72 hours prior to the test
When using Easy@Home drug test dip cards and Easy@Home and Areta cups, accuracy is key for reliability.
The goal is to avoid false negatives and false positives. Being aware of what you ingest and what can cross-react is most important. Following the testing instructions closely can help avoid a false negative. Also make sure you are testing for the correct substance’s metabolite and that you are aware of the cutoff level when reading your results.