A drug test report says one of a few things: negative, positive, dilute, invalid, substituted or adulterated. Each means something different, and in workplace testing the first lab result is often not the final one. The result that counts is the one a Medical Review Officer (MRO) has verified. This guide shows what each line on a report means and what an employer or employee should do next.

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TL;DR

  • A positive on a screening test is presumptive. In federally regulated testing it must be confirmed by the lab and then reviewed by an MRO before it becomes a verified positive.
  • A positive shows a substance was present in the detection window. According to NIDA, a drug test is not a measure of current impairment.
  • Negative dilute means no drug was found, but the specimen was more watery than normal. The employer decides whether to retest, and the rules differ by program.
  • Invalid, substituted and adulterated are specimen problems, not drug findings. Each triggers a different next step.
  • Do not act on a preliminary lab number. Wait for the MRO-verified report.

Table of Contents

Two reports, not one

People often say they are waiting for their drug test results as if one document existed. In a regulated workplace program there are usually two stages.

Stage one is the laboratory result. The lab screens the specimen, confirms any presumptive positive with a second, more specific method, and also checks that the specimen looks like normal human urine or oral fluid. Its report is technical: drug classes, concentrations and validity findings.

Stage two is the MRO’s verified result. The MRO is a licensed physician who reviews the lab data, talks with the donor when needed, and decides whether there is a legitimate medical explanation. The employer acts on this report.

Lab findings move through MRO review to employers

An MRO’s guidance, in plain terms: the most useful thing a reader can do is separate the raw lab data from the verified final result. According to a SAMHSA MRO guidance document, the MRO weighs the lab findings, the donor’s explanation and any procedural errors before issuing a decision. Employers who act on unverified lab data risk acting on a result that is later cancelled.

The main result types

Result What it means What usually happens next
Negative No drug or metabolite at or above the cutoff, and a normal specimen Nothing further. The donor can proceed (pre-employment, return to duty and so on)
Negative dilute No drug found, but the specimen is more dilute than normal Employer policy or program rules decide whether to recollect
Positive (lab) A drug or metabolite was confirmed at or above the cutoff Goes to the MRO. It is not final yet
Verified positive The MRO found no legitimate medical explanation Employer takes action under its policy and, for DOT, the federal rules
Verified negative after MRO review The MRO accepted a medical explanation, such as a valid prescription Reported to the employer as negative
Invalid The lab could not get a valid result from the specimen MRO follows set steps, which may include a new collection
Substituted or adulterated The specimen is not consistent with human urine, or something was added MRO interview, then a verified result
Cancelled A procedural or technical flaw made the test unusable Often a recollection

The exact terms can vary between a federal DOT test and a non-regulated panel. The logic is the same.

How to read a negative result

A negative is the result most people get. It means that no tested drug or metabolite was at or above the cutoff level. It does not mean the person has never used anything. A drug can be present at a level below the cutoff and still be reported as negative.

For rapid cup or strip tests, check the control line first. On many of these devices a line in the control area shows the test ran correctly. If the control line is missing, the test is invalid and must be repeated, no matter what the other lines look like. Follow the instructions printed on the specific device, since designs differ.

Workplace rapid screens are only screens. A non-negative reading on a cup is sent for lab confirmation, not treated as a finding.

Negative dilute: what the result really says

“Negative dilute” is one of the most searched terms on this topic, and it causes the most confusion. It contains two separate findings:

  1. Negative: no drug was detected at or above the cutoff.
  2. Dilute: creatinine and specific gravity were lower than expected for typical urine. That can happen when someone drinks a lot of fluid before a test. It can also happen for ordinary reasons, such as diuretics, a medical condition, or simple hydration.

A dilute specimen is still a valid result. The concern is that a very dilute sample could hide a drug that would have been above the cutoff in a more concentrated one. That is why some employers ask for another collection.

In DOT-regulated testing, the Department of Transportation’s Part 40 guidance on section 40.197 explains that the rules do not require an employer to hire anyone, and that an employer is authorized to obtain one additional test after a negative dilute result. Whether to do so is the employer’s decision, and the section sets out the conditions. If you are an HR lead, put your retest approach in writing before a dilute result arrives, and apply it to every candidate in the same way.

If you are the donor, a negative dilute is not a failed test. Ask the employer or the collection site what the next step is, and follow the collector’s instructions on fluids if you are asked to come back.

How to read a positive result

A positive means a drug or its metabolite was found at or above the cutoff concentration. Cutoffs are written in nanograms per milliliter (ng/mL). One ng/mL is a very small concentration, so a number on its own tells you little unless you know the cutoff for that drug and that test.

Three points keep a positive in perspective.

A screen is not a conclusion

Initial screens are usually immunoassay tests. Clinical reviewers, including those writing in American Family Physician, note that immunoassays can react to other substances, including some over-the-counter and prescription medications. That is the reason for confirmatory testing with a more specific lab method, followed by MRO review, in a compliant program.

A positive does not show impairment

Per NIDA, a result tells you a substance was present. It does not tell you how much was taken, how often, or whether the person was impaired at the time. A urine result reflects a window of past exposure, not the state of the person on shift. If you need to assess fitness for duty today, a drug test alone is not that assessment. Our piece on fit-for-duty testing and 24-hour MRO results covers how employers approach that question.

Context matters in the lab data

The Mayo Clinic Proceedings review of urine drug test interpretation warns that misreading these results can have serious consequences for the person tested. Metabolites, timing and cross-reactivity all affect what a number means.

What the MRO does with a positive

When the lab reports a confirmed positive, the case goes to the MRO. In DOT programs, the MRO begins by telling the employee what the lab found, as set out in 49 CFR 40.135. The MRO then asks about prescriptions and other possible medical explanations.

The MRO’s role is a gatekeeping one. Under section 40.149, an MRO may change a verified result only in limited situations, which shows how seriously the verified result is treated.

Some drug classes have special rules. For opiates, section 40.139 sets out what the MRO must look for, including the presence of 6-acetylmorphine, before verifying certain positives. A person who took a prescribed opioid may be reported as negative after MRO review, though the MRO may also raise a safety concern about the medication with the employer.

If you are the donor, keep these practical points in mind:

  • Have a list of your prescriptions and the prescriber’s contact details ready.
  • Respond when the MRO’s office calls. A missed call can delay your result.
  • Do not stop or change a prescribed medication on your own because of a test. Talk to your prescriber.

Invalid, substituted and adulterated results

These three describe the specimen, not drug use.

  • Invalid: the lab could not produce a usable result, for example because of an interfering substance or abnormal characteristics. Under 49 CFR 40.159, the MRO has to discuss the lab findings with a certifying scientist and follow set steps, which may lead to another collection.
  • Substituted: the specimen does not look like normal human urine.
  • Adulterated: something was added that should not be in a urine specimen.

Specimen validity testing matters as much as the drug panel. The oral fluid version is described in section 40.92. In an audit, missing documentation about how an invalid result was handled can create a compliance problem even when no drug was involved.

Reading a report line by line

Layouts differ by lab, but most reports cover the same ground:

  1. Donor and specimen identifiers. Check that the specimen ID matches the custody and control form, and that the name and date are correct.
  2. Collection details. Date, time and type of collection (pre-employment, random, post-accident and so on). The reason for the test matters for what the employer may do.
  3. Drug panel. The drug classes tested. A DOT panel is fixed. A non-DOT employer panel can be broader. Our DOT 5-panel guide covers the federal list.
  4. Result for each class. Negative, positive or a similar label, sometimes with a concentration.
  5. Validity findings. Normal, dilute, invalid, substituted or adulterated.
  6. MRO statement. The verified result and the date. This is the line the employer files.

If you see a concentration in ng/mL next to a drug, compare it with the cutoff stated on the report, not with a figure from the internet. Cutoffs differ between urine and oral fluid, between federal and non-federal programs, and between initial and confirmatory tests. The Department of Health and Human Services publishes panel and cutoff updates for federal programs, which is one reason a printed table from a few years ago can be wrong.

What employers should do with each result

Negative: file it, and move forward with the hire or return to duty. For DOT pre-employment tests, the clock on other requirements still runs, so see our DOT pre-employment test checklist.

Negative dilute: follow your written policy. Apply it uniformly.

Lab positive, no MRO report yet: do nothing. Premature adverse action on a preliminary report can create legal exposure. Wait for the verified result.

Verified positive in a DOT program: reporting duties start. Per the FMCSA’s MRO page, verified positive, adulterated or substituted results must be reported to the Drug and Alcohol Clearinghouse within two business days of the MRO’s determination, and employer-discovered violations such as refusals or an alcohol concentration of 0.04 or higher within three business days. Records of positive results must be kept for five years. Our guide to FMCSA Clearinghouse queries explains how that connects to hiring, and the alcohol testing rules guide covers the 0.04 threshold. The driver also has to complete the return-to-duty process, including follow-up testing.

Invalid or cancelled: document what happened and arrange the recollection the MRO or the rules call for.

What employers should do with each result — overview diagram

What we see at the clinic

We run a walk-in clinic in the Bronx, and the same few misunderstandings come up again and again.

  • Employers treat a rapid screen as a verdict. A cup that shows a non-negative is a reason to send the specimen for confirmation, not a reason to end a conversation with a candidate.
  • Donors assume a positive means they are finished. Many are not told that an MRO call is the next step, and that a valid prescription can change the outcome.
  • Dilute results get handled differently person to person. The fix is a written policy, applied the same way each time.
  • Paperwork gaps cause more audit pain than test outcomes. A result with no MRO verification on file, or an invalid test with no record of the follow-up, is what an auditor notices.

Our view is simple: the verified report is the only report to act on, and the file should show every step from collection to MRO decision. That is why we build our process around MRO-reviewed results and audit-ready documentation for DOT, OSHA and USCIS purposes, and why we aim for results within 24 hours so a hold on a hire or a driver stays short.

— Total Tox

Testing with MRO-reviewed results in the Bronx

If you need a test where the result comes with MRO review and a paper trail you can hand to an auditor, we offer walk-in urine, saliva (oral fluid) and hair follicle testing, plus DOT drug and alcohol testing and DOT and employee physicals. You can see everything on our services page. Collections typically take under 15 minutes, and results typically arrive within 24 hours. We serve clients in the Bronx and across Bronx, New York, Westchester and Queens counties. If you are deciding between hair and urine for a non-DOT program, the hair follicle vs. urine comparison lays out the trade-offs. For more compliance topics, browse our blog.

Common mistakes when reading results

  • Comparing your number with an online chart. The cutoff on your report is the one that applies.
  • Treating dilute as positive. It is a negative with a specimen-quality flag.
  • Reading ‘not detected’ as ‘never used’. A negative reflects the cutoff and the detection window.
  • Reading a positive as proof of intoxication. It shows presence, not impairment.
  • Skipping the MRO call. Donors who do not respond lose their chance to give a medical explanation.
  • Acting before verification. For employers, this is the costliest error.

FAQ

How do I know the result of my drug test?

Your employer or the clinic usually tells you, or the MRO’s office contacts you if the lab reports a non-negative. Negative results are often reported to the employer directly. If you are waiting, ask the employer or the collection site how and when results are delivered, since procedures vary by program.

Does a negative dilute mean I failed?

No. It means no drug was found at or above the cutoff, but the specimen was more dilute than normal. In DOT-regulated testing, the Department of Transportation’s guidance says an employer is authorized to obtain one additional test after a negative dilute result, but the decision belongs to the employer. Ask what the employer’s policy is.

Can a prescription medication cause a positive result?

It can. Some medications can trigger a screening result, and others are true positives for a drug you were prescribed. The AAFP review notes that screening tests can cross-react with common medications, which is why confirmation and MRO review exist. Tell the MRO about all prescriptions when they call.

What does 50 ng/mL mean on a drug test?

It is a concentration: 50 nanograms of a substance per milliliter of specimen. It is usually a cutoff, the level at or above which a test is called positive for a given drug. Cutoffs differ by drug, test type and program, so check the cutoff printed on your own report.

Can an employer fire me over an unverified positive?

In a regulated program, the employer should wait for the MRO-verified result. Acting on a preliminary report can create legal risk for the employer. If you are in this position, speak with an employment attorney or your state labor agency about your specific situation.

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