There are currently four ways to screen for THC or its metabolites: urine, saliva, blood, and hair tests. Each method has a different detection window, which determines how long THC can be detected in your system. The threshold set for a "positive" result also varies depending on the test.
Urine tests are the most common method used to screen for THC. They can detect THC metabolites for up to 30 days after use, depending on factors such as frequency of use and the amount consumed. Saliva tests, on the other hand, can detect THC for up to 72 hours.
Blood tests are more invasive but can provide an accurate measure of recent THC use. THC can typically be detected in the blood for up to 2-7 days, depending on various factors. Hair tests have the longest detection window, potentially detecting THC use for up to 90 days or more.