Why Can Cannabis-Positive Samples Outnumber the Patients They Represent?
Urine test counts and patient counts answer different questions. Smiley-McDonald and colleagues analyzed 194,809 pain-management specimens for which clinicians had requested marijuana testing over six months.
Why repeated tests matter
Patients submitted between one and 42 specimens. The investigators accounted for clustering by patient when testing statistical differences. The descriptive positivity measures still describe the specimens selected for testing. They cannot be read as the percentage of all pain-management patients who used cannabis, or compared directly with a population survey asking about past-month use.
How to read a test history
Ask whether the count refers to specimens, visits or unique people. In one person’s record, determine whether positive results were collected on different dates and what the method measured. Repeated positives do not by themselves identify separate episodes of use or establish impairment at a particular time.
