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How To Read Drug Test Results From The Lab

Understanding drug test results can be a little confusing so let’s look at how to read drug test results from the lab, and what the results actually mean.

Drug testing is commonly used by employers who want to keep workplaces safe and productive. If you’re a new manager or business owner dealing with employee drug testing for the first time, it’s important to interpret lab results correctly and to follow state and federal laws regarding any action you take after a positive test.

How To Read Drug Test Results From The Lab 2024

How To Read Drug Test Results From The Lab

When you receive a drug test lab report, you’ll see the list of substances tested for alongside the cutoff level for each substance, followed by “none detected” or “positive”.

Some labs will list the substance and cutoff level, then state whether the overall result is positive or negative. If it’s positive, the drug or drugs found will be listed underneath.

Confusion can arise because you see a list of of drugs with numbers beside them but the result will state that the sample is negative. For example, a lab report could list:

  • Amphetamine 1000 ng/ml
  • Cocaine 300 ng/ml
  • Marijuana 50 ng/ml
  • Opiates 2000 ng/ml
  • Phencyclidine 25 ng/ml

And then state that the overall result is negative.

Without understanding that the list is simply a list of substances tested for, you could assume that all of those drugs were found in the sample at those amounts and wonder why the test result states that the sample was negative.

Similarly, if you see a list like this, you could be scratching your head wondering how drugs could be present and not detected at the same time.

  • Amphetamine 1000 ng/ml – none detected
  • Cocaine 300 ng/ml – none detected
  • Marijuana 50 ng/ml – none detected
  • Opiates 2000 ng/ml – none detected
  • Phencyclidine 25 ng/ml – none detected

Read correctly, however, taking the first line as an example, you would understand that amphetamine was tested for using a drug screen with a cutoff level of 1000 ng/ml. No amphetamine above the cutoff level was detected, therefore the result for amphetamine is none detected or negative.

Let’s explain further by looking at cutoff levels.

Understanding Cutoff Levels On A Drug Test Lab Report

Understanding Cutoff Levels On A Drug Test Lab Report

Drug tests don’t return a positive result unless the amount of the drug detected is higher than the cutoff level. Cutoff levels are measured in ng/ml or nanograms per milliliter for urine and saliva tests, and picograms per milligram for hair follicle tests.

If the testing lab is using a low cutoff threshold, then you could receive false-positive results. For example, eating poppy seeds on a bagel can result in a positive opiate result, and taking an antihistamine, or cold medicine could give a false positive amphetamine result.

On the other hand, if the lab is using higher cutoff levels, you could receive false-negative results because drugs were present but the cutoff level wasn’t reached.

In the lab, urine specimens and saliva samples are divided into two parts. One part is tested using an initial immunoassay screening technique. When a sample tests negative at this stage, no further testing is required.

A drug could be present in the sample but because the amount detected is below the cutoff level, the test report will state, none detected, not detected, or negative.

If a drug is present in an amount above the cutoff level, then the sample is positive and a confirmatory test will be run on the second part of the sample to determine which substances are present and at what level.

Confirmatory tests often use a lower cutoff level for some drugs than the initial tests. If testing on the second part of the sample detects drugs above that cutoff level then the sample will be reported as positive and the substances detected will be listed on the lab report.

But before a positive drug test is sent to you, the result will be confirmed by a Medical Review Officer (MRO).

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What Does The Medical Review Officer Do?

The MRO is a licensed physician who is trained to interpret drug test reports.

The MRO will contact the test subject and ask about any over-the-counter or prescription medication they take that could have affected the test result.

For example, if a sample was positive for a barbiturate, the employee had a current prescription for the drug and the levels of the substance found were consistent with the correct use of the prescribed amounts, then the MRO would amend the result, and the lab report sent to you would show a negative result.

And if the subject has recently used an over-the-counter antihistamine which the MRO considered consistent with the levels of amphetamine detected in the sample, the result would be changed.

When no medical reason can explain the presence of a drug in the sample, the MRO certifies the result as positive and signs the report which is then sent to you.

If you need to contact the MRO for further clarification, you’ll find the physician’s contact details on the report.

Understanding What The Drug Test Looked For

Understanding What The Drug Test Looked For

The first thing to understand is that drug tests only reveal the presence of substances tested for. That statement might seem obvious, but there are different drug tests that test for various drugs.

On a 5-panel drug test, for example, only 5 drugs are tested for, and the lab report will tell you nothing about other drugs the candidate or employee may be using. A 5-panel drug screen tests for:

  • Opiates
  • Cocaine
  • Marijuana
  • Amphetamines and methamphetamine
  • Phencyclidine (PCP)

A negative result on a 5-panel test is not any guarantee that the person tested isn’t using other drugs that can impair their performance, reduce their productivity, or increase their risk of a workplace accident.

A 10-panel drug screen looks for a wider range of substances. In addition to the drugs screened for on a 5-panel test, a 10-panel drug test looks for:

  • Benzodiazepines
  • Barbiturates
  • Methadone
  • Methaqualone
  • Propoxyphene

And an extended panel includes a test for Oxycodone and Ecstasy.

So, let’s say you used a 5-panel drug screen to test an employee who appeared to be under the influence of “something”. In this case, you’ll receive a lab report with results for only those 5 substances. If the drug they used isn’t tested for, then they’ll pass the drug test, which could leave you more than a little bewildered if you witnessed their intoxicated behavior.

What Does A Negative Dilute Result Mean?

If you receive a report with a “negative dilute” result, it means that the subject tampered with their sample to cheat the test.

When a sample is diluted, fewer drug metabolites are present and that will result in a negative test. One way people attempt to cheat a urine test is by drinking lots of water before their test so that they produce weak urine which is mostly water.

Labs check samples for several kinds of cheating, and they check for urine dilution by measuring the level of a protein called creatinine. Creatinine should be present in normal urine at a certain level, if the level of creatinine is too low, then they know the sample has been diluted.

A diluted sample will test negative for drugs, but instead of reporting the results as negative, the lab will indicate that cheating occurred because of the low creatine level.

Drug Test Detection Windows

A drug detection window is a period that a drug can remain in a person’s body and be picked up on a test.

Whether you’re drug testing candidates to avoid hiring drug users or carrying out random drug testing to weed out drug users already on staff, the drug testing method you use will determine what you can learn.

An oral fluid drug test (saliva test) has the shortest detection window and won’t reveal drug use that occurred more than 48-72 hours ago.

While a saliva screen is useful for employee drug testing, it has obvious limitations as a candidate screening tool. Because the detection window is so short, knowledgeable candidates simply abstain for a couple of days when they have an interview coming up.

A urinalysis drug screen has a detection window of 4 to 7 days for most drugs, 14 days for phencyclidine, and up to 90 days for marijuana. In some ways, it’s more difficult to pass because of the longer detection window, yet it can also be the easiest test to pass if a person is inclined to cheat, because of the easy availability of fake urine which can pass all the lab’s adulteration checks.

A hair follicle drug test can’t be tampered with and it has a long, 90-day detection window. The drawback of this testing method is it can pick up drug use in someone who no longer uses drugs but used them in the past.

Summing Up

The drug test results you receive from the lab will list all of the substances the sample was screened for. You’ll also see the cutoff level for each substance listed alongside the name of the drug.

The lab report may state “positive” or “not found” next to each substance, or it may simply record an overall negative result, or a positive result. If it’s positive, the specific substances will be recorded underneath.

You could also receive a drug test result that shows a false negative result because the sample was tampered with in some way.

If you’ve got any questions about the report, contact the lab and they’ll be happy to explain the report to you.

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