What is a false negative drug test? - City of drug testing (2023)

What is a false negative drug test? - City of drug testing (1)

Most people are familiar withfalse positives on drug tests, but are unaware of false negatives. What is a false negative on a drug test, what can you do to avoid it, and what should you do if you spot one?

What is a false negative drug test?

A false negative is any time when, under normal circumstances, a drug test would be positive for an individual, but for some reason the results are negative. An example would be an oxycodone prescription patient who consistently takes the prescribed medication but has a negative drug test during the doctor's visit.

In most cases, this is because the patient alters his urine sample on purpose or accidentally. The most common false negative drug test is due to water loading.

False negatives of water charging and adulteration

Water charging is the process in which a person drinks an excessive amount of water before giving a sample. Clear urine without yellow coloring is usually indicative of water load. You will need to run separate tamper tests for creatinine, pH, and protein levels to demonstrate that a test has been diluted by an individual who has ingested excessive amounts of water.

What is a false negative drug test? - City of drug testing (2)

Without adulteration tests, pure water will show a negative result on a drug test test because the tests are only intended to detect the presence of a particular drug or metabolite in a substance, not to detect whether the substance is a valid sample. . Subjects can simply add water to their urine, but to deceive a witness, they drink an excessive amount of water to dilute the urine that comes out of their own body.

(Video) City worker fired twice over 'false positive' drug test

There are several products available that claim to help users pass urine drug tests. These products range from nothing more than fortified tea that dilutes the urine to products that claim to seal in fat cells for several hours. Many of these products speed up the amount of time a person can pass a urine test, even if it's no more than diluting the urine.

Incorrect selection of drug tests

One mistake that drug testing organizations make is incorrect test selection. Each organization will have its own considerations when choosing a testing device, but some drug tests will not detect all illicit substances that people assume.

semi-synthetic opiates

Often, a physician prescribes their patient oxycodone or another semi-synthetic opioid, but uses a 5-panel drug test that only has one test for opioids. The doctor saw his patients who were prescribed oxycodone test positive for opioids, but his new patient tested negative.One study found that oxycodone was detected in 12% of opioid immunoassay tests, and many other synthetic or semi-synthetic opioids also require a special test for accurate results.


Most benzodiazepine assays detect their presence in urine by testing nordiazepam and oxazepam, the major metabolites of most benzodiazepines. Agents that follow a different metabolic pathway, such as triazolam, alprazolam, clonazepam, and lorazepam, show little cross-reactivity with the assay due to the absence of these metabolites and therefore often produce false-negative results. Some physicians prescribe diazepam, oxazepam, and temazepam to reduce laboratory confirmations.

False negatives from cut-off levels that are too high

If your drug tests have high cutoffs, a user who has recently used drugs is more likely to produce a negative result.

HeNational Institute on Drug Abuseit's himSubstance Abuse and Mental Health Services Administrationpublish the recommended cut-off levels for drug testing that most companies follow. Dozens of other federal agencies publish their own default limits (everyone from the Department of Transportation to the Nuclear Regulatory Commission) that are often based on federal recommendations.

(Video) 5 ways you could falsely test positive for drugs

Although the federal government publishes its own guidelines, labs and manufacturers can create products that use any cutoff level they deem appropriate, and federal guidelines change from time to time.

For example, opiates and morphine have two cut-off levels that have been widely used since the early 2000s because many people were failing job tests due to the popularity of poppy seed muffins. The recommendation skyrocketed from 300 ng/ml to 2,000 ng/ml. Most tests will use this recommendation to meet as many federal regulations as possible, but highly sensitive tests are still available.

What is a false negative drug test? - City of drug testing (3)

In practice, there is no correct answer. Some regions may have popular restaurants that sell poppy seed muffins, and some industries may have a high percentage of customers who anticipate testing and use gray hat tampering methods to keep their levels below the threshold.

human error

We advertise our drug tests as 99% accurate, but in any situation involving a human being there is the possibility of introducing human error. A technician can mislabel labels, forget to confirm the temperature on a sample, or give the patient the opportunity to completely change a sample.

Human error is even more likely in a lab where a technician needs to set up a test, control variables, process and record information, and interpret results. Never completely rule out human error and implement procedures that can help reduce the likelihood of human error.

faulty device

Since the consequences of a failed drug test can be so severe, a lot of work and investment goes into quality control of drug testing devices. Still, there are always some faulty tests or test batches that slip through the cracks.

(Video) How to Pass a Drug Test (After Doing Lots of Drugs) | Vanity Code | Vanity Fair

If you have multiple tests in a row that give unexpected results, consider that the tests might be faulty. It is very cheap and easy to use a second drug test if a subject says his results are not accurate.

Our drug test cups are designed to alert the user when there is a problem with the device itself. The control line can alert you to tampering, faulty testing, and some forms of incorrect collection.

What is a false negative drug test? - City of drug testing (4)

Note that a12 panel drug testthere are actually 12 individual tests; most of the time a bad device means only one of the strips is bad. A certain percentage of faulty tests is expected in this industry, so we offer a 100% satisfaction guarantee that covers any faulty device and any additional tests you use to fix a potential faulty test.

Other anomalies

There are times when all the devices are working properly, everyone has done everything they are supposed to do, and a sample is valid in every way, and there is still a false negative result on the drug test.

the hook effect

A rare cause that has been addressed by manufacturers in recent years is the "hook effect," in which so much drug is present in the urine that there are no more binding sites on the antibody. This can cause a lower apparent level which could lead to a negative result if below the cut-off level.

drug degradation

One of the benefits of using a drug test cup is that the receptacle is also the test. There is no time gap between collection and testing. In a busy doctor's office, technicians can be distracted or intentionally multitask when working on test results.

(Video) Here's what your drug test will look like

When sent to a lab, it can take even longer between collection and testing. Time in transit and whenever the shipment sits in the lab without adequate refrigeration gives the sample more time to naturally degrade.

Most metabolites are stable for the brief periods usual in drug testing, but others are not stable, especially when subjected to temperature changes or extremely high temperatures.

An example is 6-monoacetylmorphine (6-MAM), a metabolite of heroin. On bodyheroin is metabolized to 6-MAM, which is then metabolized to morphine.6-MAM lacks stability, is subject to in vitro hydrolysis, and also continues to be metabolized to morphine even after urine leaves the body. One study showed that within 7 days at room temperature, a urine sample that tested positive for 6-MAM was completely hydrolyzed to morphine.

Limiting false negatives in drug tests

Understanding that a false negative is a possibility and the possible causes is the first step in stopping them. Collecting and storing data can be an important part of investigating unexpected or suspicious results.

With sufficient knowledge and proper analysis, many drug test results inconsistent with expectations can be reconciled and explained. Here are some other tactics you can use to limit the chance of false negatives in your drug testing program.

  • Institute procedures and policies to combat the charging and adulteration of water.
  • Use a 12-panel drug test to cover many of the synthetic and semi-synthetic opioids
  • Understand cutoff levels and detection times for the tests you use
  • Institute policies and procedures that reduce the likelihood of human error
  • Report faulty tests to the manufacturer or reseller


What makes a drug test false negative? ›

False-negatives can occur when the urine drug concentration is below the threshold level set by the laboratory performing the test. Dilute urine, the duration of time between ingestion of the drug and time of testing, and the quantity of the drug ingested may affect the occurrence of false-negatives.

How do you fight a false drug test? ›

Consult a specialist who can represent and support you through the process.
  1. Step one: be transparent. If you use prescription medications or regularly eat foods like poppy seeds, notify the person testing you so they can take this into account. ...
  2. Step two: consult a professional. ...
  3. Step three: opt for a re-test.
Mar 23, 2022

What is a false drug test? ›

A false positive is when a drug test shows the presence of a medication or substance that you didn't actually take. Multiple medications can cause false positive results. Some examples include NSAIDs, dextromethorphan, and some antidepressants.

Can drug tests come back false? ›

Unfortunately, drug test results are not 100% accurate, and false positives may occur. “False positives” are when drug tests flag a medication or substance you do not actually take. Sometimes, these are caused by lab errors, but certain medications have also been known to trigger fictitious positive results.

What is a false negative urine test result? ›

A false negative error, or false negative, is a test result which wrongly indicates that a condition does not hold. For example, when a pregnancy test indicates a woman is not pregnant, but she is, or when a person guilty of a crime is acquitted, these are false negatives.

What can interfere with drug test results? ›

What Can Cause a False Positive Drug Test
  • Secondhand Marijuana Smoke. 1/11. If you hang out often with someone who puffs on pot, your urine could have traces of THC. ...
  • Weight Loss Pills. 2/11. ...
  • Poppy Seeds. 3/11. ...
  • Mouthwash. 4/11. ...
  • Antidepressants. 5/11. ...
  • Antibiotics. 6/11. ...
  • CBD Oil. 7/11. ...
  • Antihistamines. 8/11.
Sep 5, 2021

How do I know if I passed my drug test? ›

How do you know if you passed a pre-employment drug test? If the drug test results are returned as negative that means no evidence of the substance was detected in the specimen. If the test shows a positive result, that generally means evidence of the substance was detected.

What is the false positive rate for drug tests? ›

In other words, even though there's only a 1% overall error rate – which seems pretty good – 50% of the positive tests are false positives. That doesn't sound like a very high probability for violating your client's probation or supervised release and putting him or her in prison.

What happens if a drug test comes back positive? ›

If the test results in a positive reading, meaning there is drug residue in the body, the results are forwarded to a medical review officer, who reviews the results and looks for any possible valid medical explanation for the results. “As a medical review officer, I would review a patient's medical history.

How long does Delta 8 stay in your system? ›

Because their structures are similar, delta-8 is expected to stay in the body for the same amount of time as delta-9 THC. For occasional users, this could be as little as 2 to 5 days. For regular users, it could be up to 15 days.

How long will ibuprofen show up on a drug test? ›

After ingestion of one single oral dose of 400 mg ibuprofen, the parent compound could be detected for 27 to 34 h, hydroxy ibuprofen for 34 to 40 h and carboxy ibuprofen for 5 to 6 d.

Does a drug test have 1 percent false positive? ›

Consequences of false-positives

In fact, some data suggests 5 to 10 percent of all drug tests may result in false positives and 10 to 15 percent may yield false negatives.

How to delay pre employment drug test? ›

Good excuses to postpone a drug test
  1. You are sick. ...
  2. You got into an accident. ...
  3. Your babysitter bailed. ...
  4. You have to babysit. ...
  5. You are going out of town. ...
  6. You are having an allergic reaction. ...
  7. There must have been an error with the test. ...
  8. You are on a medication that skewed the results.
Feb 27, 2023

How far back can a lab drug test detect? ›

Drugs in hair may be detectable for approximately 90 days, whereas drugs in urine are generally detectable for one to seven days or longer in chronic users and in oral fluid from five to 48 hours.

Which drug tests are accurate? ›

Blood testing is expensive and invasive, but is the most reliable for determining if the individual is under the influence of drugs or alcohol right now. Hair testing has the longest detection window, nearly 90 days, and is the least invasive method of all, but also has the highest cost.

Can you have a false negative test? ›

Negative result.

This means that you likely don't have an infection with the COVID-19 virus. But a false-negative test result could happen depending on the timing and quality of the test sample. If you have symptoms, stay away from others. Your doctor may recommend repeat testing if you continue to have symptoms.

Can not enough urine cause false negative? ›

Can a pregnancy test come up negative if I didn't pee enough? A false negative on a home pregnancy test is possible, but extremely unlikely. As long as your urine got on the test's absorbent strip, it should be accurate. You can always take another test if you're worried you might have missed.

Can diluted urine cause false negative? ›

Diluted Urine

Another potential cause of a false pregnancy test is if the urine used for testing is too diluted. If the urine is not concentrated enough, then there may not be enough hCG in it for the test to detect.

Can a UTI affect a drug test? ›

Will a UTI affect the result of drug and/or alcohol testing? Certain bacteria may interfere with drug detection but will not generate a false positive. Fermenting bacteria in the presence of excess glucose may produce ethanol in the bladder and in the specimen cup.

How can I avoid testing positive for drugs? ›

WASH YOURSELF OUT: The general strategy for passing urine tests is to increase your fluid intake and urine flow so as to dilute the concentration of drugs in the sample below the threshold of detection. An hour or two before the test, you should fill your bladder with fluids – as much as you can drink.

Can you spike a drug test? ›

However, some patients alter their test results by adding buprenorphine directly to their urine sample to imply adherence, a new study shows. In the study, nearly 2% of all urine drug test specimens analyzed were suggestive of spiking and nearly 8% of patients had at least one specimen that was possibly spiked.

What is the most common false positive drug test? ›

Amphetamine (more on this below) and methamphetamine are the most commonly reported false positive.

What are interfering substances in urine? ›

The interfering drugs include ascorbic acid, beta-lactam antibiotics (e.g., cephalosporins and penicillins), levodopa, and salicylates. Several other drugs may also interfere with certain urine glucose tests, but the interactions are poorly documented.

Can a UTI cause a negative drug test? ›

Will a UTI affect the result of drug and/or alcohol testing? Certain bacteria may interfere with drug detection but will not generate a false positive. Fermenting bacteria in the presence of excess glucose may produce ethanol in the bladder and in the specimen cup.


1. How To Pass A Drug Test Every Time (2018)
(National Drug Screening)
2. medications that give false positive results with drug test
(الصيدلة و الناس)
3. False drug test almost costs a mom her children
(WCPO 9)
(Dope Guru)
5. Hair Follicle Drug Test—Pros & Cons, Myths, and How It Works
(David Bell)
6. Don't give fake pee to this guy
(Kansas City Star)


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