What Is the Difference Between a Screen and a Confirmation?
For healthcare organizations and professionals (B2B) · Physician-led · Updated 2026-07-12 · CLIA #45D2048957 · CAP #8722734
A presumptive positive is not a result. It is a question.CLIA #45D2048957 · CAP #8722734 · Same-day results · Walk-ins welcome
Presumptive (immunoassay) testing uses antibodies that react to a structural class. It is fast and inexpensive, and it is vulnerable to cross-reactivity in both directions: false positives from unrelated compounds, and false negatives for drugs the antibody was never designed to see. Definitive testing (LC-MS/MS) identifies the specific molecule and quantifies it. The two are not interchangeable.
Where each one fails
| Failure | Example | Consequence |
|---|---|---|
| False positive (cross-reactivity) | An amphetamine-class screen reacting to an unrelated compound | A patient is accused, discharged, or loses their prescription — wrongly |
| False negative (blind spot) | Standard opiate screens do not detect fentanyl | The most dangerous drug in the sample is invisible |
| No quantitation | "Positive" with no concentration | Cannot assess consistency with a prescribed regimen |
| Class, not molecule | "Amphetamines positive" | Cannot distinguish prescribed from illicit — see this |
The correct workflow is: screen where appropriate, confirm before acting. A clinical or administrative consequence should never rest on an immunoassay alone.
FAQ
- Do we always need confirmation?
- Confirm before any consequential decision, and whenever the result is unexpected or contested.
- Is screening useless then?
- No — it is a reasonable, inexpensive first pass. It just is not a finding.
- What about fentanyl?
- It is not detected by standard opiate immunoassays. It must be targeted specifically — see this.
- Can you reflex to confirmation automatically?
- Yes, with a defined protocol built on medical necessity — see compliance.
References
- CDC — Clinical Practice Guideline for Prescribing Opioids
- ASAM — Clinical Guidelines (Appropriate Use of Drug Testing)
- SAMHSA — Substance Use Treatment Resources
- Our CLIA #45D2048957 and CAP #8722734 credentials — verify them yourself
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