Many employers have expressed confusion on the interpretation of “dilute” specimens and what action they should take after a drug test reported as “negative – dilute”. In this blog, let’s first examine how the certified laboratories arrive at this result. In parallel to the actual testing for the requested panel of drugs, laboratories perform a series of tests to validate the integrity of the urine specimen. One such test is the measurement of the creatinine concentration in the submitted sample. Creatinine is a byproduct of muscle metabolism that is excreted by the kidneys at a rate of approximately 1 milligram per minute. The concentration of creatinine in a random urine specimen is a function of the donor’s fluid intake prior to collection. If the creatinine in a specimen is less than 20 milligrams per deciliter (mg/dL), this is indicative of abnormal or excessive fluid intake in the hours before collection. In the laboratory process, when the creatinine is less than 20 mg/dL, another test is reflexed which is the measure of the specimen specific gravity. Specific gravity measures the density of dissolved compounds in the urine (water has a specific gravity = 1.0000). If the creatinine is less than 20 mg/dL and the specific gravity is less than 1.0030, the laboratory is required to report the specimen as “dilute” in conjunction with the actual drug test determinations.

The reporting of a “dilute” result is the difficulty in the interpretation of the drug test. A donor may produce a specimen which is “dilute” for totally innocent reasons ( i.e., an athlete who consumes lots of fluids per his/her conditioning program, medical reasons on the advice of a physician, weight loss protocols,etc.) A donor MAY also drink excessive amounts of fluids in an attempt to “flush drug residues from their system” prior to their drug test. Many products are available in “head shops” and the internet that encourage drug users to utilize the product to beat the test. Most are used in conjunction with copious quantities of fluids which will have the result we have discussed. In the interpretation of the “dilute” specimen, MROs, TPAs, and employers have difficulty in determining the reasoning behind the donors excessive fluid intake.

An employers substance abuse and testing policy should clearly designate what actions should be taken when a “negative-dilute” result is reported. These actions may include a repeated test after discussion with the donor either at the donors expense or company authorization, the agreement to perform a random test at an unannounced later date, or acceptance of the original result with no ramifications. Whatever decision is made, it’s vitally important to be consistent and not apply different rules for different employees.