Consuming large amounts of fluid to pass a mandatory urine drug test is a common strategy. The simple answer is that excessive water intake dilutes the urine sample, lowering the concentration of drug metabolites. However, modern drug testing laboratories use strict procedures and chemical checks specifically designed to detect this manipulation. Attempting to dilute a sample is a high-risk strategy because it rarely goes unnoticed and can lead to consequences similar to a positive result.
How Excessive Hydration Affects Urine Concentration
The underlying theory behind drinking excess water is based on the physiology of waste elimination. When a person consumes a large volume of water in a short period, the body responds by increasing urine production to maintain fluid balance. This rapid and excessive fluid intake causes the urine to become physically dilute.
Drug screenings use established cutoff thresholds, which are the minimum concentrations of a metabolite required to report a positive result. Over-hydration aims to push the metabolite concentration below this laboratory-determined limit, resulting in a false negative.
However, the dilution of drug metabolites also lowers the levels of naturally occurring substances. Laboratories identify an abnormally watery specimen by checking these normal chemical markers. The excessive amount of water needed to significantly dilute metabolites below the cutoff level will almost certainly dilute the sample below validity thresholds.
Laboratory Markers Used to Identify Dilution
Testing facilities employ specific scientific checks known as specimen validity tests to ensure a sample is genuine, undiluted human urine. These checks focus on two intrinsic chemical markers that should be present in consistent concentrations: creatinine and specific gravity. The integrity of a urine sample is flagged as questionable if these markers fall outside a normal physiological range.
Creatinine is a waste product of muscle metabolism that is excreted by the kidneys at a relatively constant rate. Over-hydration causes the concentration of creatinine in the urine to drop sharply due to the increased water volume. A creatinine level below 20 milligrams per deciliter (mg/dL) is commonly used as a laboratory standard to classify a sample as dilute.
The second primary marker is specific gravity, which measures the ratio of dissolved particles to the total volume of the liquid. This assesses the density of the urine sample relative to water. Normal urine contains various solutes, such as salts and urea, giving it a specific gravity in the range of 1.003 to 1.030. A low specific gravity, typically below 1.003, indicates that the sample is composed of an abnormally high percentage of water, confirming the presence of excessive dilution.
Common Attempts to Mask Dilution
Individuals sometimes attempt to mask the visual and chemical signs of a diluted sample using various substances. One common technique is the use of high-dose B-vitamins, particularly riboflavin (Vitamin B2), which turns the clear, colorless urine of an over-hydrated person bright yellow. This addresses the visual cue of dilution, as a clear sample raises immediate suspicion among collection staff. However, B-vitamins do not affect the chemical markers of dilution and fail to restore the low creatinine or specific gravity levels to an acceptable range.
Another method involves ingesting creatine supplements in the days leading up to the test to artificially raise the urinary creatinine level. Creatine is a precursor that the body converts into creatinine, which is then excreted. While this can sometimes elevate the creatinine concentration above the 20 mg/dL threshold, it is often ineffective at correcting the specific gravity, which remains abnormally low due to the excessive water intake. Moreover, laboratories are increasingly aware of this form of matrix adulteration and may flag samples with a disproportionately high creatinine level coupled with low specific gravity for further investigation.
Outcomes of a Diluted or Invalid Test Result
When a laboratory identifies a sample as dilute, the result is reported back to the testing authority, which determines the subsequent action based on their policy. A dilute result is usually categorized in one of two ways: “negative dilute” or “positive dilute.”
A positive dilute result means that the drug metabolite concentration was still high enough to exceed the cutoff threshold despite the excess water. This result is treated the same as a standard positive test result.
A negative dilute result indicates that no drug metabolites were detected above the cutoff, but the sample validity markers were too low. This result is considered inconclusive, and the test subject is generally required to provide a second sample under stricter observation. Depending on the regulatory body, a second negative dilute result may be accepted as a negative test or treated as a refusal to test. The primary consequence of a dilute result is the delay of employment or disciplinary action due to the suspicion of sample tampering.