Choose the defensible laboratory action

First decide what the request is trying to answer. Urine is commonly used for metabolite detection, while oral fluid is more recent-use oriented and uses different federal workplace cutoffs. Hair can show a longer historical pattern but carries external-contamination concerns and is not federally authorized for workplace testing.

Meconium and umbilical cord tissue answer a prenatal exposure-history question, whereas newborn urine reflects only very recent exposure. Meconium generally reflects later pregnancy exposure but cannot establish an exact exposure date, and a negative result does not exclude earlier exposure. The specimen and method are therefore chosen together, not after a result is already released.

For an unexpected clinically important class-screen finding, review the specimen, test menu, medication context, and local reflex policy. If definitive identification is needed, use the laboratory's validated GC-MS or LC-MS/MS pathway. Do not state that a presumptive screen proves a specific drug, impairment, dose, or timing.

Select the matrix and analytical tier that answer the stated question, then communicate the remaining uncertainty. Apply the local reflex policy when definitive testing is needed. Keep the released conclusion bounded.