Yes, you can request a drug test retest in most situations, and the mechanism is usually the same: the second half of your original sample gets sent to a different certified laboratory for independent analysis. If your test falls under federal Department of Transportation rules, you have 72 hours from the moment a Medical Review Officer notifies you of a verified positive result to make that request. If your test is governed by a private employer’s policy or a state statute, the deadline and procedure depend on those specific rules. Before you make the request, though, it’s worth knowing that the testing process has two built-in checks that resolve many disputed results on their own.
Two Checks Happen Before You Hear About a Positive
A drug test isn’t a single pass/fail event. When your specimen reaches the lab, it goes through an immunoassay screening first. That screen is fast but prone to cross-reactivity with legal medications and foods. Anything the immunoassay flags gets rerun on the same specimen using gas chromatography-mass spectrometry or liquid chromatography-mass spectrometry, which identify specific drugs and concentrations with much greater accuracy. Only results positive on both tests move forward.
The second check is the Medical Review Officer interview. Before your employer hears anything, a licensed physician trained in substance abuse testing reviews the confirmed positive and contacts you directly and confidentially to discuss it.1eCFR. 49 CFR 40.131 This is where you explain prescriptions, medical conditions, or other legitimate reasons for the result. If you take a prescribed amphetamine for ADHD, for example, the MRO can verify the prescription and change the result to negative on the spot.
You have to speak with the MRO personally; their staff can only schedule the call. If they can’t reach you, they must make at least three attempts over 24 hours before contacting your employer’s designated representative to help locate you, and even then, they cannot disclose the result.1eCFR. 49 CFR 40.131 Once the MRO verifies the result as positive (or you decline to speak with them), you’re formally notified, and the retest clock starts.
How the Split Specimen Works
The retest system relies on a split specimen. At collection, your urine is divided into two bottles: a primary of at least 30 mL that goes to the lab, and a split of at least 15 mL that stays sealed and stored.2eCFR. 49 CFR 40.71 – How Does the Collector Prepare the Urine Specimen If you dispute a verified positive, the split gets sent to a different certified laboratory for independent testing.
All DOT collections must use this method. Many private employers follow it voluntarily because it’s the industry standard, but they aren’t legally required to unless a state law mandates it.
Making the Request Within 72 Hours
For DOT-regulated employees, you have 72 hours from MRO notification to request a test of the split specimen. The request can be verbal or written.3U.S. Department of Transportation. 49 CFR 40.171 – How Does an Employee Request a Test of a Split Specimen The MRO is required to tell you about this right when they notify you of the result, explain how to contact them, and stay reachable throughout the window.4U.S. Department of Transportation. 49 CFR 40.153 – How Does the MRO Notify Employees of Their Right to a Test of the Split Specimen
Miss the 72 hours and you’re not automatically out. You can present evidence to the MRO that something beyond your control blocked a timely request: serious illness, inability to reach the MRO’s office, or lack of actual notice of the result. The MRO has discretion to grant a late request in those circumstances.3U.S. Department of Transportation. 49 CFR 40.171 – How Does an Employee Request a Test of a Split Specimen
When you make the request, state clearly that you are requesting a test of the split specimen. Note the date, time, and who took the request. If you called, follow up in writing the same day. Ambiguity here is what causes disputes later about whether a valid request was even made.
Non-DOT and State-Law Deadlines
If you don’t work in a DOT-regulated role, the 72-hour rule doesn’t apply to you. Your rights come from your employer’s written drug testing policy, the consent form you signed, and any state drug testing statute that covers your situation. Some states give employees five working days to submit a written retest request. Others allow much longer windows. A handful require employers to notify employees of retest rights alongside the positive result; many don’t.
The deadline is the single most important detail to confirm, because missing it usually means losing the right entirely. Read your employee handbook and check your state’s drug testing statute before doing anything else.
Who Pays
Under DOT rules, you cannot be required to pay out of pocket before the split specimen test happens. Your employer must ensure the test occurs on time regardless of whether you can or will pay. They can seek reimbursement later through company policy or a collective bargaining agreement, but they cannot use nonpayment as a reason to block or delay the retest.5eCFR. 49 CFR 40.173 – Who Is Responsible for Paying for the Test of a Split Specimen
Outside DOT testing, cost rules vary. Some state laws put retest costs on the employee. Many private employer policies include cost-sharing provisions. Expect a bill somewhere between roughly $50 and $200 depending on the substances confirmed and the lab. Find out who pays before you make the request, but don’t let the question push you past your deadline.
What the Retest Can Produce
Once you make a timely request, the MRO directs the original laboratory to send your sealed split specimen to a second certified lab, which runs its own confirmation testing independently. There are three possible outcomes.
- The split confirms the original positive. The result stands. For DOT-regulated employees, that means removal from safety-sensitive duties and a mandatory evaluation by a substance abuse professional before returning to work. For non-DOT positions, your employer’s policy sets the consequences.6Federal Motor Carrier Safety Administration. Return-to-Duty
- The split fails to reconfirm. The test is cancelled entirely. The MRO reports the cancellation to your employer and to the DOT’s Office of Drug and Alcohol Policy and Compliance. A cancelled test is not the same as a negative test, and in some situations the employer may be directed to collect a new specimen immediately.7eCFR. 49 CFR 40.187 – What Does the MRO Do With Split Specimen Results
- The split is unavailable. If it was lost, damaged, or no lab can test it, the test is cancelled. The employer must then immediately collect a new specimen under direct observation, with no advance notice.7eCFR. 49 CFR 40.187 – What Does the MRO Do With Split Specimen Results
One limitation matters: federal regulations do not allow alternative tests on the specimen, such as DNA analysis to prove whether the sample is yours. Only the authorized split-specimen retest is permitted.4U.S. Department of Transportation. 49 CFR 40.153 – How Does the MRO Notify Employees of Their Right to a Test of the Split Specimen
Why Positives Get Disputed
Not every positive result reflects actual drug use, and knowing the common causes helps you make the most of the MRO interview before you even get to a retest.
Prescription and Over-the-Counter Medications
Bupropion (Wellbutrin, Zyban) is one of the most well-documented causes of false positives for amphetamines on immunoassay screens.8PubMed. Frequency of False Positive Amphetamine Screens Due to Bupropion Using the Syva EMIT II Immunoassay Sertraline (Zoloft) has been linked to false positives for benzodiazepines with certain immunoassay methods.9PMC. False-Positive Urine Screening for Benzodiazepines: An Association With Sertraline Decongestants containing pseudoephedrine, some NSAIDs, and certain cough suppressants can also trigger initial screening flags, though most get filtered out during laboratory confirmation.
Bring your pharmacy records to the MRO call. Waiting until the retest stage to raise a medication issue that could be resolved immediately wastes both time and your chance at the simplest fix.
Food and Legal Supplements
Poppy seeds contain trace amounts of morphine and codeine. Federal workplace testing guidelines set the confirmation cutoff for morphine at 4,000 ng/mL specifically to reduce false positives from poppy seed consumption.10Federal Register. Mandatory Guidelines for Federal Workplace Drug Testing Programs – Authorized Testing Panels A large quantity eaten shortly before testing can still push levels above the threshold.
CBD and hemp-derived products are a newer concern. Legal hemp must contain no more than 0.3% THC by dry weight, but some products exceed that limit or contain enough THC to register on a screen. Research from Johns Hopkins Medicine found that even a single use of hemp-derived products could produce a cannabis-positive urine result on standard workplace tests.11Johns Hopkins Medicine. Some CBD Products May Yield Cannabis-Positive Urine Drug Tests
Collection and Chain-of-Custody Errors
Mistakes in collection, labeling, transport, or storage can compromise a result. If the documented trail from collection to analysis has a gap or inconsistency, the result may be invalid on its face. Raise this with the MRO before requesting a split-specimen test, because a chain-of-custody defect could get the test cancelled outright.
Court-Ordered Testing Works Differently
If your positive result came from a court-ordered test connected to probation, parole, drug court, or a custody proceeding, the DOT split-specimen protections do not automatically apply. Courts set their own testing protocols. Challenging a result means filing a motion with the court rather than calling an MRO, and the consequences (revocation of probation, custody changes) can be immediate. Talk to your attorney before the court acts on a disputed result.
If Your Test Was Oral Fluid
As of December 2024, DOT-regulated employers can use oral fluid (saliva) testing as an alternative to urine.12U.S. Department of Transportation. Part 40 Final Rule – DOT Summary of Changes The federal mandatory guidelines now include separate cutoff levels for oral fluid, including panels for opioids and fentanyl.10Federal Register. Mandatory Guidelines for Federal Workplace Drug Testing Programs – Authorized Testing Panels If your test used oral fluid rather than urine, ask the MRO specifically about your retest options, because split-specimen procedures may differ.
What to Do Now
- Check the clock. The 72-hour DOT deadline is strict. Other deadlines may be shorter or longer. Find your specific window and work backward.
- Talk to the MRO first. A prescription or medical explanation can resolve the issue without any retest. Gather pharmacy records before the call.
- Make the request clearly. State that you are requesting a test of the split specimen. Note the date, time, and who took the request. Follow up in writing.
- Don’t let cost stop you if you’re covered by DOT rules. Your employer cannot block the retest for nonpayment. For non-DOT testing, ask about costs, but don’t miss the deadline over the question.
- Read your employer’s policy and your state’s drug testing statute if you’re not in a DOT-regulated role. Those documents control your rights.