Screening vs confirmation: why a positive is not final

Two steps, two different jobs

Most drug testing follows a two step approach. First, a fast, low cost screening test checks whether a drug class may be present. Second, if the screen is positive and the result matters, a more precise laboratory method confirms it (Hadland and Levy, 2016).

• Screening (immunoassay)

  Uses antibodies that react to a drug or drug class. Fast, affordable and available as on-site cups. Results are qualitative: positive or negative relative to a cutoff.

• Confirmation (GC-MS or LC-MS)

  Separates the sample’s chemicals and identifies them by molecular signature. Specific, quantitative and performed in a laboratory.

SAMHSA explains that screening tests are usually immunoassays giving qualitative results, while confirmatory tests use GC/MS or LC/MS, provide quantitative results, and must be performed in a laboratory (SAMHSA TAP 32).

Why screens can be wrong

Immunoassays are sensitive but less specific than mass spectrometry because the antibodies can react to substances that look chemically similar (Hadland and Levy, 2016). Some well documented examples:

• Pseudoephedrine, a common decongestant, can produce a positive amphetamine screen (SAMHSA TAP 32).
• Phentermine, a weight loss medication, commonly causes a false positive initial amphetamine result (SAMHSA TAP 32).
• Dextromethorphan, found in cough medicine, can trigger a PCP screen in some assays (SAMHSA TAP 32).
• Selegiline and bupropion have been reported to cross-react with amphetamine screens (StatPearls).
• Poppy seeds contain low levels of morphine that sensitive tests can detect (Hadland and Levy, 2016).

Screens can also miss things. A negative screen does not rule out use, and a basic opiate screen may not detect several synthetic opioids (StatPearls).

When confirmation is worth it

SAMHSA’s guidance is clear: point-of-care results are presumptive, and if a patient disputes a positive result, or if legal or employment consequences are possible, a laboratory confirmation test should be done (SAMHSA TAP 32). In practice, that covers most situations people care about:

• The person tested says they did not use.
• The result will be shared with an attorney, a court, an employer or a professional program.
• A family is about to make a big decision based on the result.
• A clinician needs to know exactly which substance is present, for example to tell a prescribed medication from a non-prescribed one.

Federal workplace testing builds confirmation into every positive: specimens that screen positive are retested by a more specific method at a confirmatory cutoff before a result is reported (SAMHSA Mandatory Guidelines, 2023). The same logic protects families and people in recovery.

When confirmation might not change much

Sometimes a person openly acknowledges use before or right after a positive screen. In that case, many families and clinicians skip confirmation and move straight to the conversation about what happens next. That is a reasonable choice. Confirmation exists to protect people from acting on a wrong result, not to add a hurdle when everyone already agrees on what happened.

What a confirmed result tells you, and what it does not

A confirmed positive tells you that a specific substance or its byproduct was present above a set level. It does not tell you:

• Whether the person was impaired at the time.
• Exactly when or how much they used.
• Whether they have a substance use disorder.

NIDA notes that drug testing does not diagnose a substance use disorder and that results should not be the sole basis for decisions about care (NIDA). For alcohol biomarkers like EtG, Mayo Clinic Laboratories advises interpreting results in the context of all available clinical and behavioral information (Mayo Clinic Laboratories).

What to do while you wait for confirmation

1. Pause big decisions. Confirmation usually takes a few days. Avoid irreversible steps based on a screen alone.
2. List medications and products. Write down prescriptions, over the counter medicines and supplements from the past week. See testing and prescriptions.
3. Talk, do not interrogate. A calm conversation now makes the next step easier whatever the result.
4. Plan for both outcomes. If the result is confirmed, our guide on what to do after a positive test can help.

How Blackburn Monitoring can help

At Blackburn Monitoring, instant screens give you a fast first answer, and presumptive positives can be sent to our partner laboratories for confirmation. When results are needed for legal or professional purposes, we provide chain of custody documentation. Results are shared quickly and only with the people you authorize in writing, and a coordinator who knows you is available to talk through what a result means. Testing is low cost and by appointment in Los Angeles.

Read about our lab confirmation process, our 12 panel urine drug test, or how monitoring works. If a confirmed result shows someone needs more care, your coordinator can introduce you to therapy and psychiatric care at Blackburn Clinical Services.