Skip to main content

The Importance of Definitive Drug Testing

The results from Dylan’s drug test are back, and they show presence of an opioid-consistent with the oxycodone you’ve prescribed him. No problem, right?


Detecting the parent drug won’t rule out the possibility that Dylan is “pill shaving” to pass the test, while diverting the bulk of the medication. What can you do to rule out pill shaving?

Pill shaving refers to the practice of scraping or crushing part of a pill to dissolve it in a urine sample.

Common reasons for pill shaving include:

  • to test positive for a prescribed medication the patient has not taken, often because the patient has diverted it for sale or trade for another substance or is saving it for use later.
  • to adulterate someone else’s urine and then submit it for testing as their own, because the patient’s own urine will show presence of illicit or unprescribed medications.

Detection of pill shaving requires definitive testing

Many patients receiving a prescription for controlled substances may take their medication as directed. But access to medications, such as opioids or benzodiazepines, presents an opportunity to sell or trade medications to those who are not authorized to receive them. Drug diversion is a major source of prescription medication misuse. It poses risks to those receiving the medication, and risks for patients who should be taking it but are not.

Many healthcare providers assume that a presumptive drug test, or screen, is all they need to ensure their patients are taking the prescribed drug, and that a positive test result for the prescribed drug class indicates prescription adherence.

This is simply not so. A presumptive test can only tell you whether the urine sample contains the drug class. A presumptive test should be confirmed using definitive analysis. Presumptive testing alone cannot tell you whether your patient ingested it or added it to the urine at collection in order to fool the test.

A patient who has diverted their prescribed medications may keep one or more pills to “shave” into the urine sample which can lead to a positive presumptive drug class result, consistent with the prescription. The test should then be confirmed using definitive methodology. The definitive test, using chromatography and mass spectrometry, will identify the drug metabolites in addition to the parent drug - the only proof that the drug has been ingested and metabolized, rather than mixed into the sample after excretion (which happens more often than most clinicians think).

Case history

Dylan Tomkins, a 29-year-old Caucasian male, presented to your office one month ago as a new patient with chronic back pain he attributed to a motorcycle accident when he was 19. He had no other complaints. He was not currently taking any medication for his pain, as his prescription from a previous clinician had run out. He reported his pain as a 7 out of 10.

The physical exam was unremarkable except for mild limitation of truncal rotation. Neurologic exam was normal.

He reported he had been seen by “a couple” other clinicians in the past 6 years and received prescriptions for oxycodone.

A baseline drug screen from an unobserved urine collection, performed using a point-of-care drug test cup, showed no sign of illicit or controlled substances.

At that visit, you prescribed oxycodone 40 mg twice daily, and asked him to return for a follow-up visit and urine drug test at one month.

At the follow-up, Dylan reports his pain is 2 out of 10. The urine sample is again collected unobserved.

You order a presumptive screen for opiates and oxycodone, with an automatic reflex for definitive testing. Three days later, results come back:

  • Presumptive test for oxycodone: Positive
  • Definitive test for oxycodone and metabolites: positive for oxycodone, negative for metabolites (noroxycodone, oxymorphone)

Question: Is Dylan taking his medication?

Answer: Dylan is almost certainly not taking his oxycodone as prescribed. The absence of oxycodone metabolites (noroxycodone and oxymorphone) in the definitive test results indicates he has not taken the drug within the detectable period (1-3 days). And the positive oxycodone result? It means that oxycodone was present in the urine sample. This is likely due to adulteration of the urine sample through pill shaving. You can use this objective result to have a candid conversation with the patient to understand why the patient isn’t taking the prescribed drug.

Oxycodone isn’t the only prescription medication liable to be diverted. Other opioids, benzodiazepines, and methamphetamine, along with other drugs, have a street value, and may be sold or traded. Definitive testing for the prescribed drug and the metabolites is the best way to detect whether your patient has actually taken the prescribed medication. To ensure that patients are taking the prescribed drug, definitive drug test results must be positive for the associated drug metabolite. If they are positive for the prescribed parent drug but negative for drug metabolite, it means that while the drug was present in the urine sample, it was not ingested and metabolized in the body.

Moving forward when you find evidence inconsistent with your treatment plan

No clinician wants to consider that their patient has likely been diverting their prescription medications. No test results can identify diversion. But results from a drug test give you objective information you can use to begin a conversation to understand what is going on with the patient.

That conversation most often begins with presenting the evidence in a nonthreatening way, and explaining the conclusion you draw from it, and why. This opens the dialog with facts, not suspicions or accusations. Some patients might deny they have diverted, while others might be honest. Outcomes may include:

  • If the patient still needs a prescription medication, consider more frequent testing and requiring the patient to bring in the pill bottle to show the remaining medication. Both activities are designed to increase the likelihood of compliance.
  • A dose reduction may be indicated, to better match the patient’s actual need for treatment, reducing the likelihood of diverting excess pills.
  • Discontinuation of the prescription is also an option if the patient indeed does not need the medication.

Published date: June 11, 2019