Written by: John Mallios, Senior Director, Occupational Health Services at Sterling Infosystems
An issue that often arises in workplace drug testing is that of a "diluted" drug test result reported by a testing laboratory or a Medical Review Officer (MRO), and how such a result should be treated by an employer.
In basic terms, a diluted test simply means that there is a greater concentration of water in a urine specimen than what would be expected for "normal human urine." Though a laboratory may establish that a specimen is diluted, this does not necessarily mean that a valid drug test cannot be conducted.
A diluted result is generally reported as either "Positive Dilute" or "Negative Dilute." If a drug test is reported as "Positive Dilute," the urine specimen is positive for a drug or metabolite that the employer is testing for. Consequently, this is a failed drug test and can be treated as such without further consideration of the dilution. If, however, a test is reported as "Negative Dilute," thereby indicating that there's no positive detection of a drug or metabolite in the specimen, the employer must then determine how the dilution should be addressed. That question is the focus of this article.
Specimen Validity Testing
Obviously, consumption of water or other fluids will affect urine production in one's system. If a donor (job applicant or employee) consumes excessive quantities of fluid prior to providing a urine specimen for workplace testing, the test may very well be reported as diluted. Many times, dilution of a urine specimen is quite innocent and inadvertent. Sometimes, however, dilution can signal an attempt by a donor to cheat the drug testing process by reducing the concentration of a drug/metabolite in the specimen. This deliberate effort to over-consume fluids is often referred to as "water-loading." Of course, a donor can also dilute a specimen by directly pouring water into the specimen cup before returning it to the collector during the collection process. (Dilution should not be confused with specimen adulteration, which involves direct addition of chemical material to the specimen).
Before testing for actual drugs/metabolites, a laboratory will first test the urine specimen to establish that its content is consistent with "normal human urine," and that there is no apparent attempt on the part of the donor to cheat. This is known as "Specimen Validity Testing" (SVT).
SVT analytical standards are established by the Department of Health & Human Services (HHS) and are necessary for federally mandated drug testing programs. With every specimen, SVT requires certified laboratories to:
- Determine the creatinine concentration
- Determine the specific gravity for which creatinine measures less than 20 mg/dL
- Determine the pH level
- Perform one or more validity tests for oxidizing adulterants
- Perform additional testing based on specimen quality, interference or other atypical result
For a urine specimen to be considered "normal human urine":
- Creatinine must measure greater than or equal to 20 mg/dL.
- Specific gravity must measure greater than or equal to 1.0030.
- pH must measure between 4.5 and 9.0.
- No oxidizing adulterant(s) can be identified.
The creatinine concentration in the urine specimen is the primary measurement for identifying dilution in SVT (creatinine comes from the normal physiological breakdown of muscle tissue). If a urine specimen contains no creatinine, it is not likely to actually be urine. If a specimen does contain creatinine, this means that at least a portion of it is urine, but it is no guarantee that the entire specimen is "normal human urine."
A urine specimen that is not otherwise invalidated will be reported as diluted by the laboratory if:
- Creatinine measures less than 20 mg/dL, and
- Specific gravity measures less than 1.0030.
An employer's workplace testing policy should articulate the employer's position surrounding receipt of a "Negative Dilute" result and how it will be treated. Testing performed under an employer's own authority (e.g., not federally mandated) may, for example, require a donor to immediately submit to another urine specimen collection following the report of a "Negative Dilute" result (this is a common practice). In some instances, employers might require a recollection using an alternate specimen methodology, such as hair or oral fluid, while others may establish requirements similar to those used for federal testing, such as the DOT (Department of Transportation), which has very specific requirements for treatment of a "Negative Dilute" result.
Under DOT testing rules:
- If the creatinine level is greater than or equal to 2 mg/dL but less than or equal to 5 mg/dL, the MRO will order an immediate recollection under direct observation (meaning the donor must be physically observed providing the urine specimen).
- If the creatinine level is greater than 5mg/dL but less than 20 mg/dL, the donor may, at the employer's discretion based on company policy, be required to submit to immediate recollection. If the employer does, however, adopt a policy of recollection:
- All "Negative Dilute" results with creatinine levels greater than 5mg/dL but less than 20 mg/dL must be consistently treated without variation.
- The employer must accept the second test result as the final test result of record.
- The recollection must not be performed under direct observation for reasons other than Return-To-Duty or Follow-Up testing (or unless other aspect of the collection so dictates).
- A donor's refusal to submit to a recollection following instruction to recollect must be treated as a refusal to test (a DOT rule violation).
- Recollection can be limited to pre-employment or post-hire testing, or even to specific testing reasons (random selection, post-accident, etc.).
An employer's decision regarding how diluted results will be handled should also consider other factors, such as safety risks associated with individual employee work functions (i.e., high or low risk) or treating a regulated employee differently than a non-regulated employee. Still, whether for employer-based or federally mandated testing, proper communication in the employer's policy of how a diluted result will be managed is necessary for a consistent and effective workplace testing program.