The Ethyl Glucuronide (EtG) test is a common urine-based method used to detect recent alcohol consumption, often employed in programs that require abstinence or monitoring. This test looks for a specific byproduct of alcohol metabolism, offering a much longer detection window than standard breath or blood tests. Laboratories have developed specific procedures to identify samples that have been intentionally diluted in an attempt to manipulate the results.
Understanding the ETG Test and Alcohol Metabolism
The EtG test focuses on Ethyl Glucuronide, a stable, water-soluble metabolite of ethanol, the alcohol found in beverages. When ethanol is consumed, the liver metabolizes most of it through oxidation. However, a small percentage is processed through a non-oxidative pathway to create EtG and Ethyl Sulfate (EtS). Since EtG is a direct byproduct of alcohol, it remains in the body long after the intoxicating effects have worn off.
The presence of EtG in urine serves as a reliable marker indicating recent ethanol consumption. This metabolite is filtered by the kidneys and excreted into the urine over time. Depending on the amount consumed, EtG can be detected in the urine for up to 80 hours or more, providing a much wider detection window than tests measuring only alcohol.
EtG is considered a persistent marker because it is produced by the liver over a period of hours following consumption, making it challenging to eliminate quickly. While EtG is water-soluble, drinking a large amount of water cannot instantly remove all the EtG already produced and stored in the body. The testing process accounts for the concentration of the urine itself, which challenges individuals attempting to dilute the sample.
How Labs Identify Diluted Samples
Laboratories do not rely solely on the concentration of EtG to determine the result; they also perform “validity checks” to assess the integrity of the urine sample. These checks are designed to detect whether the sample has been diluted by excessive fluid intake before collection. The two primary markers used to flag a potentially diluted sample are creatinine and specific gravity.
Creatinine is a waste product generated by muscle metabolism and is normally excreted by the kidneys at a relatively stable rate. Rapidly consuming a large volume of water flushes the urine quickly, drastically lowering the concentration of all solutes, including creatinine. Laboratories typically flag a sample as potentially diluted if the creatinine concentration falls below a certain threshold, often 20 milligrams per deciliter (mg/dL).
The second measure is specific gravity (SG), which quantifies the concentration of dissolved particles, or solutes, in the urine relative to the density of water. Normal urine has a range between 1.002 and 1.030. Excessive water consumption significantly lowers the SG because the concentration of solutes is reduced. If the specific gravity falls below a certain value, typically 1.003, the sample is definitively flagged as dilute.
These two integrity checks work together to prevent attempts at dilution from being successful. Even if water intake lowers the EtG concentration below the positive cut-off, the accompanying low creatinine and low specific gravity values will flag the sample as diluted. Some advanced testing methods also use a creatinine-normalized ratio (EtG/Creatinine) to account for variations in concentration and reveal the true EtG level.
Consequences of an Invalid or Diluted Result
When a urine sample is flagged as diluted because creatinine and specific gravity levels are outside the acceptable physiological range, the result is not reported as a simple negative. A diluted result indicates the sample’s concentration is too low to reliably confirm the presence or absence of the target metabolite. This outcome is often treated administratively as an invalid test result.
In many contexts, such as probation, court-ordered testing, or employment monitoring, an invalid or diluted result is considered a violation of the program’s rules. Depending on the specific program’s policy, a diluted result may be treated as equivalent to a positive test for alcohol use. In other instances, a diluted result automatically triggers the requirement for an immediate, supervised retest.
The consequences of a diluted sample are generally procedural and can include sanctions, a delay in program completion, or program failure. The administrative response effectively nullifies the attempt to dilute the sample, as the test subject is still penalized or forced to retest under stricter observation. This process ensures the integrity of the monitoring program is maintained.