What Makes LC-MS/MS the Definitive Method?
For healthcare organizations and professionals (B2B) · Physician-led · Updated 2026-07-12 · CLIA #45D2048957 · CAP #8722734
Immunoassay guesses at a class. LC-MS/MS identifies the molecule and quantifies it.CLIA #45D2048957 · CAP #8722734 · Same-day results · Walk-ins welcome
Two independent dimensions of identification. Liquid chromatography separates compounds by their physical and chemical behavior; tandem mass spectrometry then fragments each compound and measures the mass of its fragments — a structural fingerprint. The result is specific identification of the individual analyte, with quantitation, rather than an antibody reacting to whatever in the sample happens to look similar.
Screening vs. definitive
| Immunoassay screen | LC-MS/MS | |
|---|---|---|
| Identifies | A drug class, presumptively | The specific molecule and its metabolites |
| Cross-reactivity | A known, frequent problem | Not applicable — identification is structural |
| Quantitation | No | Yes |
| Defensibility | Presumptive only | Definitive — suitable as a confirmatory result |
| Blind spots | Fentanyl is missed by standard opiate screens | Fentanyl and norfentanyl targeted directly |
A presumptive positive is a hypothesis. Acting on it — clinically or administratively — without definitive confirmation is how people lose medications, jobs and custody over a cross-reaction.
Why quantitation matters clinically
In medication monitoring, the question is often not "present or absent" but "consistent with the prescribed regimen." That requires a number, and a metabolite pattern — see medication monitoring.
FAQ
- When is definitive testing warranted?
- When the result will drive a clinical or administrative decision, when a screen is unexpected, or when the drug of interest is invisible to the screen — fentanyl being the sharpest example.
- What is the turnaround?
- See turnaround and logistics. We will give you an SLA, not a vague promise.
- Is your lab accredited?
- CLIA #45D2048957, CAP #8722734 — the quality system behind it.
- Can you customize the panel?
- Yes — custom UDT panels, built on medical necessity, not on maximizing billable analytes.