Last updated: October 2, 2023
While that last cup of coffee or glass of water will not adversely affect your urine drug test, consuming large quantities of fluid may, but not in the way that some people believe.
Despite one of the most common myths about drug testing, flushing your system with excess fluids will not hide or mask drug use. This is because drug metabolites—the biological byproducts of drug use—will still show up in a test sample, and consuming excess fluids will cause your body’s creatinine levels to be out of the normal range. (Also note that consuming large quantities of fluid will not affect mouth swab or hair follicle drug tests in any way.)
Creatinine levels that are out of the normal range may indicate that someone attempted to hide or mask drug use. When drug metabolites are not detected, in conjunction with creatinine levels that are out of the normal range, results in a negative dilute drug test result. 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 and will result in termination if conducted under a program for federal employees or a DOT drug test. When it is not part of a federally regulated program, an employer must follow their documented policy for positive results. If the result is a negative dilute, many drug testing policies will require employees to return for another drug test.
Where DOT regulations rule
A specimen with creatinine levels (a waste product in the blood created by the normal use of muscle cells) of 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 collection under direct observation.
The result of a required retest following a negative dilute report, for current employees taking part in a return-to-duty test or a follow-up test, must under DOT regulations render a negative result. An applicant with a second directly observed negative dilute urine test result will not be eligible for hire under the employer’s uniformly enforced policy.
Of course, if the employee declines a retest required due to a dilute specimen, it will be considered a “refusal to be tested” and treated as a confirmed and verified positive result, and the offer of employment rescinded or current employment terminated.
Where the employer decides
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 place before the fact that allows the practice.
- All employees are treated equally.
- The re-collections are not observed re-collections.
- Only one re-collection is allowed; the result of the second collection to be the result of record, 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.
As with a DOT drug test, when an employee declines a retest required due to a dilute specimen, it will typically be considered a “refusal to be tested” and is 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.
A policy statement must already be in place
Under both DOT and non-DOT drug testing programs, the decision for handling a negative dilute drug test result is up to the employer, who should have a documented drug testing policy prior to conducting a drug test. 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 normal if the person consumes large amounts of water normally for, say, health reasons. Or they may have done so on this one occasion out of concern for being able to produce a specimen. Policy statements can set those standards of action. On the other hand, if the specimen is a positive dilute, the “dilute” aspect is of minimal interest and the documented drug testing policy for a positive result must be followed.
Avoiding a negative dilute result
Once again, avoid consuming too much fluid before a drug test, and avoid too much caffeine or other diuretic intake, both of which can cause a negative dilute drug test result. Any attempt on an employees’s part to dilute the sample will likely be both identified, and taken as an attempt to cheat on the test.
The best advice is to avoid excessive fluid and/or diuretics, and if possible, don’t urinate less than two hours before your drug test. Following that, don’t drink more than 24 oz of fluid.
This will help ensure that you don’t produce a dilute drug test result.