Qualitative and Quantitative Drug Test Results
There are differences between qualitative and quantitative drug test results. Once in a while a customer asks, “Can an instant drugs-of-abuse test tell us the quantity of drugs in a person’s system?” We get another question that’s similar, “If the line on a multi-panel instant drug test is very light does that suggest that there might be just a little bit of drug present?”
The short answer to both questions is “no.” All of the on-site drugs of abuse tests on the market today are “qualitative” tests that give pass/fail results. A qualitative test result is either negative or positive. A test that can estimate the amount of drug in a specimen is called a “quantitative” test. Currently there are no instant drugs-of-abuse tests that give estimates of the amount of drug present in the specimen. The only way to get quantitative results is with a laboratory test instrument.
But what about the intensity of the lines on an instant test? (For those who have not used an instant drug test kit: a line develops to indicate a negative result; the absence of a line indicates that the specimen contains the drug, and the result is positive. A multi-panel drug test that detects several drugs will have a line for each of the drugs to be detected.) Typically on a multi-panel drug test kit with negative results, some of the lines will be darker than the other lines. And it’s typical for at least one line to be significantly lighter than the other lines; sometimes the line is very faint. While the goal of every manufacturer is to make a kit with dark, vivid lines for every drug on a multi-panel test kit, given current technology that usually doesn’t happen.
The operator may be tempted to think that the reason the line is so light is because there is a trace amounts of drugs in the specimen. That is a wrong assumption. The golden axiom in interpreting instant drug test results is that as long as the operator can see a line, the test result is negative. The operator must disregard the intensity of the lines. The operator may draw no other conclusions other than the test must be interpreted as a negative result.
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