Last updated : February 17, 2025
A negative dilute result on a drug test doesn’t mean an employee “passes” it. If they were hoping to mask drug use by consuming large quantities of fluid before the test, it may have done more harm than good.
One of the most common myths about drug testing is that flushing your system with excess fluids hides or masks drug use long enough to submit a specimen that won’t contain any drug metabolites. That’s not true. Drug metabolites—the biological byproducts of drug use—will still show up in a test sample. Moreover, consuming excess fluids will cause your body’s creatinine levels to rise above normal.
And, just for the record, consuming large quantities of fluid doesn’t affect mouth swab or hair follicle drug tests either. Mouth swab testing gathers saliva as it excretes into the mouth. The drug metabolites are in the saliva. In the case of hair testing, the metabolites grow out into the hair shaft. It leaves a permanent record of drug use.
Raising suspicion
Creatinine levels that are out of the normal range can indicate that someone attempted to hide or mask drug use. When drug metabolites aren’t detected in the specimen but creatinine levels are out of the normal range, the test is determined inconclusive. The term “negative dilute,” means creatinine levels indicated too much water in the urine. So, even though there are no drugs detected, the fact that the urine is diluted raises a red flag for employers who are wary of cheaters.
A positive dilute drug test result occurs when creatinine levels are outside of the normal range and drug metabolites are detected. A positive dilute is always considered positive. It results in termination if conducted under a program for federal employees or a DOT drug test. That’s often the case for those employed in the general workforce too.
If the result is a negative dilute, many drug testing policies will require employees to return for another drug test. Moreover, these tests are often set up to be observed.
Mandated regulations
In the case of Department of Transportation (DOT) drug testing, a specimen with creatinine levels (a waste product in the blood created by the normal use of muscle cells) greater than or equal to 2 mg/dl but less than 5 mg/dl, and specific gravity less than or equal to 1.0010 calls for the Medical Review Officer (MRO) to require the donor to return for a second drug test under direct observation.
The second test following a negative dilute report must render a negative result. An applicant with a second directly observed negative dilute urine test result will be removed from duty. In the case of a pre-employment test, the applicant becomes ineligible for hire.
Should the employee decline a required retest due to a dilute specimen, it will be considered a “refusal to test.” These are treated as a confirmed and verified positive result. The offer of employment is rescinded or current employment is terminated.
What happens if a pre-employment drug test renders a negative dilute result? The employer may refuse to hire the applicant if that is how the company’s drug testing policies are written. However, the employer can’t claim that the DOT requires this action to be taken.
Employers have a say
Non-DOT and DOT regulations under 49 CFR Part 40.197 allow the employer to decide for himself whether to have the donor return for another one-time collection ensuring the following:
- The employer has a policy statement in writing before the fact that allows the practice.
- All employees are treated equally.
- The recollections are not observed recollections.
- Only one recollection is allowed; the result of the second collection is the result listed, even if another negative dilute.
- The decision to re-collect may vary by the reason for the testing; i.e., an employer may decide to re-collect all pre-employment dilute negatives, but not random dilutes, or vice versa.
In the event of a negative result when a specimen produces creatinine levels of 5 mg/dl or greater, but less than 20 mg/dl, and the specimen’s specific gravity is greater than 1.0010 but less than 1.0200, the employer will follow their documented policy on how to handle the situation. When the lab report is negative dilute, the employer’s policy should be to either accept the result as is or have the donor return for a second collection.
When an employee of the general workforce declines a retest due to a dilute specimen, it’s typically considered a “refusal to test.” Refusals to test are generally treated as a confirmed and verified positive result, and the offer of employment rescinded or current employment terminated. This, of course, must be specified in the company’s documented drug testing policy.
Policies must be in place
Under both DOT and non-DOT drug testing programs, employers decide how to handle a negative dilute drug test result. The company should have a documented drug testing policy before conducting employee drug tests.
The only exception is when the specimen is out of range and the MRO requires a retest. This protects employers by eliminating the need to make arbitrary drug testing decisions in the heat of the moment.
In some cases, a negative dilute may be because the person normally consumes large amounts of water for health reasons. Another scenario? Someone who suffers from shy bladder syndrome, may have drunk a lot to enable them to produce a specimen. Policy statements can set specific procedures in place for these special circumstances.
On the other hand, if the test result is a positive dilute, the “dilute” aspect is of minimal interest and the documented drug testing policy for a positive result must be followed.
Avoid a negative dilute result
Most drug tests don’t reflect a negative dilute result. Just avoid consuming too much fluid before the test. Avoid too much caffeine or other diuretic-type intake. These can cause a negative dilute drug test result. Any attempt on an employee’s part to dilute the sample will likely be identified as an attempt to cheat the test.
So avoid excessive fluid—don’t drink more than 24 oz—and diuretics, and if possible, don’t urinate less than two hours before your drug test. This will help ensure you don’t dilute your drug test.
