A dilute specimen occurs when a urine specimen is used to conduct a drug test.
According to the Department of Transportation :
A “dilute specimen” is a urine sample that has a higher than average water content. The goal when diluting a sample is to minimize the drug levels visible in urine. … This can be abused by intentionally over-consuming large amounts of water prior to a drug test.
If a person drinks an excessive amount of fluids, their urine might be diluted, meaning there is more water in the specimen than actual urine. This is something measured at the laboratory with creatinine levels and specific gravity.
An employer may accept a negative/dilute test result as a negative test. If the employer wants a retest it may do so, however, it should be stated in the employer’s policy and the employer must require a retest of all individuals that have a negative/dilute result in the same testing category.
The Department’s rules do not require an employer to hire anyone. That decision is an employer’s.
While §40.197(b) authorizes an employer to obtain one additional test following a negative dilute result (in pre-employment or other testing situations), a negative dilute test result is a valid negative test for DOT’s purposes.
Because a negative dilute test result is a negative test for DOT program purposes, the employer is authorized to have the applicant begin performing safety-sensitive functions.
If the employer declines to hire the applicant in this situation, the employer’s decision is based solely on its own policy. The employer cannot claim that its action is required or authorized by DOT rules.
According to Abbott Laboratories Explanation of dilute and ultra dilute specimens there are two levels of a dilute specimen: Dilute Specimen and Ultra-Dilute Specimen.
Dilute: The lab has tested the sample’s validity and found the Creatinine to be <20 and the Specific Gravity to be > 1.0010 but < 1.0030. A dilute specimen is one that is not very concentrated. The specimen may have been diluted by excessive fluid intake (water, coffee, soda, etc.) prior to the test; however, this does not necessarily mean that the donor has attempted to tamper with the specimen. A negative dilute is a negative test. DOT negative dilute results are released with dilute comments that refer the donor to regulation 40.197 in the Federal Register.
Ultra-Dilute: The lab has tested the sample’s validity and found the Creatinine to be greater than or equal to 2 but less than or equal to 5 and the Specific Gravity to be less than or equal to 1.0010 or greater than or equal to 1.0200. DOT negative ultra-dilute results are released with dilute comments that refer the donor to regulation 40.197 in the Federal Register. Non-DOT ultra-dilute results are released with dilute comments and a recommendation for an unobserved re-collection.
You can require retesting of all negative-dilute donors. Your policy should address this situation and you must make sure to treat all individuals the same i.e. be consistent. This is a recommended action.
Want to avoid the dilute specimen scenario? We devote many of our blog posts to the advantages of oral fluid drug testing. In contrast to urine drug testing, there is no such occurrence as a dilute specimen when saliva is used as the specimen for a drug test.