Inconclusive Drug Test Results (5 Common Causes Explained)

A chemist doing work at a lab

Testing for the presence of drugs in one’s system is a frequent practice in pre-employment drug testing, joining the army, or being admitted to any highly-esteemed institution.

But what if there’s still doubt after the drug test? I have seen several cases where an employer received an inconclusive result and the different causes that led to that result. Here’s why this might occur.

Summary of the Key Findings

  • If you drink a lot of water before you give a urine sample for drug testing, the drug concentration in your urine may be too low to be detected in your drug test.
  • The longer the time between collection and examination for certain drug tests, the more likely there are external factors (like temperature) affecting the sample. ‘
  • People can add something to their urine to change the drug test results.

Defining Inconclusive Drug Test Results

A chemist holding tubes of urineInconclusive drug test results or invalid results mean that the drug test was not successful in checking for the presence of the panel drugs [1].

In order to understand what an inconclusive drug test result is, it’s important to know how drug tests work. Employers will most likely require a urine test, which can detect drugs used in the last few days. The test looks for traces of the drug in your body, specifically in your urine.

There are two types of drug tests: screening tests and confirmatory tests. Screening tests are usually immunoassays, which use antibodies to look for traces of drugs. These tests are quick and easy to do, but they’re also less accurate. If the results are positive, the employer or the medical review officer will request validity tests.

Also Read: How Long Does It Take To Get Drug Test Results?

5 Common Causes

A chemist doing lab work

1. Interpretation

The first common cause is an incorrect interpretation of the results. This usually happens with screening tests because they’re not as accurate as confirmatory tests.

The cutoff levels for positive results are different for each drug, and sometimes the cutoff level is incorrectly set. If the cutoff level is too low, it will result in more false-positive test results; if it is too high, it will result in more false-negative results.

2. Sample Collection 

The second common cause is an incorrect sample collection. A mistake that’s often made is not collecting the sample within the specified time frame. The detection window is small for certain drugs, like amphetamines, which allows us only a few hours of drug testing. So if the sample isn’t collected within that time frame, it’s likely that the drug won’t be detected.

3. Chain of Custody

The third common cause is an incorrect chain of custody. The chain of custody is the process used to track the movement of the specimen from the time it’s collected until it’s tested. This is important because it ensures that the specimen hasn’t been tampered with and that it’s been stored properly.

If there are any mistakes in the chain of custody, it can invalidate the test results. For example, if the sample isn’t collected by a trained professional or isn’t stored at the correct temperature, it can affect the results.

4. Time Between Collection and Test

The fourth common cause is the elapsed time between when the sample is collected and when it’s tested. For certain drugs, like amphetamines, the detection window is only a few hours. So if the test isn’t conducted within that time frame, it’s likely that the drug won’t be detected, which will lead to inconclusive results.

Another factor that can affect the drug test results is the storage conditions of the specimen. If it isn’t stored at the correct temperature, it can degrade and become unusable for drug testing.

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5. Diluting

The fifth and final common cause is diluting the urine specimens, which causes a diluted drug test result. This is usually done deliberately to change the drug test results. The most common way to do this is to drink a lot of water before giving a urine sample. This will dilute the concentration of the drug in their urine and will lead to a diluted drug test result [2].

“As with any scientific test, interpretation of a drug test result requires balancing a number of factors, including elements directly related to the test, the physical characteristics of the individual being tested, and the nature and length of the individual’s drug usage.”

– The US Office of Justice Programs Drug Court Clearinghouse and Technical Assistance


Why would a urine test be inconclusive?

A urine test would be inconclusive because of incorrect interpretation, incorrect sample collection, an incorrect chain of custody, abnormal physical characteristics, the time between collection and test, or diluting of the sample.

Will Quest Diagnostics call if I fail a drug test?

No, Quest Diagnostics will not call if you fail a drug test. They will only inform the employer who ordered the test.

What does a rejected drug test mean?

A rejected drug test means that the laboratory received a testing sample that hasn’t been preserved properly and hence couldn’t perform the procedure.

What to Do if Your Drug Test Is Inconclusive?

If your drug test results are inconclusive, a retest is the best thing to do. You can either take another screening test validity test to make sure if you think an employee appears intoxicated. If you take a confirmatory test, make sure that the chain of custody is followed correctly and that the specimen is stored correctly.

But before you retest, make sure that you detox entirely to ensure that the results are accurate. I would recommend that you try the Clear Choice Rescue Cleanse. It’s an all-natural detox that will help you pass any drug test and avoid any inconclusive test results.



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