A urine drug screen is a common requirement for employment or compliance, designed to detect drug metabolites—the byproducts created after the body processes a substance. A “negative dilute” result is an ambiguous outcome from this testing process. The “Negative” portion confirms the absence of drug metabolites above established cutoff levels. However, the “dilute” designation indicates the urine sample contains an abnormally high concentration of water. This effectively lowers the concentration of all other components, including potential drug metabolites, raising questions about the sample’s validity.
Understanding the Negative Dilute Status
The “Negative” portion signifies that the laboratory did not find drug metabolites at or above the pre-defined concentration thresholds. This suggests that either no drugs were present, or the concentration of any present drugs was too low to register as positive.
The “Dilute” status is determined by two objective laboratory measurements that assess urine concentration. The first is the concentration of creatinine, a waste product of muscle metabolism. A sample is flagged as dilute if the creatinine level is greater than 5 milligrams per deciliter (mg/dL) but less than 20 mg/dL.
The second measurement is the specific gravity, which compares the urine’s density to that of pure water, reflecting the concentration of dissolved solids. A sample is considered dilute if its specific gravity is less than 1.003 (or less than 1.0010, depending on the standard). These two criteria indicate the sample is overly watery, potentially masking drug metabolites that would have been detected in a normal, concentrated sample.
Common Reasons for Sample Dilution
The primary cause of a dilute sample is the excessive consumption of fluids prior to collection. This hyperhydration flushes the body, increasing the water content of the urine and reducing the concentration of waste products, including creatinine. This over-consumption may be unintentional, such as drinking large amounts of water due to nervousness or a desire to stay hydrated.
The use of diuretics also contributes to a dilute sample by promoting increased urine production. Diuretics include prescription medications for conditions like high blood pressure, as well as common beverages like coffee and tea. Some individuals intentionally over-consume fluids or diuretics to “flush” their system, though laboratories are trained to look for the resulting low concentration.
Less common physiological factors can result in low-concentration urine. Certain medical conditions, particularly those affecting kidney function, can impair the body’s ability to concentrate urine. However, in mandatory drug testing, the default assumption often leans toward excessive fluid intake, whether accidental or purposeful, as the most likely cause.
Employer Policies and Retesting Requirements
The consequences of a negative dilute result depend heavily on the specific policies of the testing organization, particularly whether the testing is federally regulated or part of a non-regulated private employment program. For employees in federally regulated positions, such as those governed by the Department of Transportation (DOT), the Medical Review Officer (MRO) reports the result, and the employer must follow strict federal guidelines. If the creatinine level is extremely low (between 2 and 5 mg/dL), the MRO is mandated to require an immediate recollection under direct observation.
For non-regulated employers, the response is determined by the company’s written drug-free workplace policy. Many employers do not accept the ambiguous result and require the employee or applicant to undergo an immediate retest. This mandatory retest is the most common response, as the initial result is not a definitive negative and suggests the possibility of a masked positive.
If a retest is required, the employee is typically given minimal advance notice to prevent another attempt at dilution. While the first retest is often unobserved if the initial creatinine was over 5 mg/dL, a second negative dilute result may be accepted or lead to further action based on company policy. Declining a required retest is generally treated as a “refusal to test,” which is considered the equivalent of a confirmed positive result and can lead to job termination or withdrawal of a job offer.