A diluted specimen is a urine test in which the sample is too diluted to provide an accurate drug testing result. According to a study published in the Journal of Food and Drug Analysis, dilution is the “most common cause of tampering of urine specimens from both workplace and court settings.” (Learn more in How To Avoid Adulteration in Employee Drug Testing). Here is what you should know about dilute specimen drug tests in your workplace.

What A Dilute Specimen Is (And Is Not)

It’s important to understand what a dilute specimen is and what it isn’t. A dilute specimen is simply a urine sample that has a higher than average water content. It is not, however, an automatic fail. Dilute specimens are defined by the Department of Transportation (DOT) as samples with creatinine and specific gravity values that are lower than expected for human urine. Creatinine is a waste product found in urine and low levels of it are the first red flag for a test. Abnormal levels of creatinine will usually lead the laboratory to next consider the specific gravity of the specimen.

In their guidelines for Medical Review Officers (MRO), the Substance Abuse and Mental Health Services Administration(SAMHSA) dictates that additional tests for specific gravity should be performed on specimens with a creatinine level of less than 20 mg/dL. Generally speaking, diluted specimens have creatinine levels of 2mg/dL and 20mg/dL. Since water has a specific gravity of 1.0000, any specimen with a specific gravity of 1.0010 and 1.0030 is considered to be dilute.

What Causes Dilution?

The first thing you should know is that it is seldom random. DOT recognizes that certain medical conditions, such as diabetes, pregnancy or kidney problems, can lead to dilution, and occasionally people can accidentally overhydrate themselves, but these cases are fairly rare. Most dilute specimens in drug tests are the result of a deliberate act by the person being tested. Dilution can be accomplished by deliberately adding additional water to a sample, but more commonly, testers will consume excessive amounts of water or another liquid prior to the test in order to dilute the urine sample.

What Happens When A Dilute Specimen Is Detected?

Labs will typically catch the dilution and once it is detected, and several things can happen.

An MRO or physician will usually be consulted to determine if a medical condition or prescribed medication is the cause for the dilution. DOT lays out the following guidelines for what can happen next and the rules that DOT covered employers must follow for any follow-up testing.

  • The MRO can direct the employer to obtain a new sample under direct observation by a same-gender technician. This is generally done when the creatinine level is more than 2mg/dL but less than 5mg/dL.
  • The employer can request a recollection if the creatinine result was more than 5mg/dL but this recollection will not be done under direct observation/observed testing.
  • The employee should be given as little advance notice as possible.
  • Only one recollection is allowed.
  • All employees must be treated equally. You either retest all dilute specimens or none.
  • The employer must notify employees of drug testing policies and possible consequences before any drug testing begins. (Learn more in The Importance of a Good Drug and Alcohol Policy in the Workplace).

Non-DOT employers will be governed by both the laws of their state and their own policies. It’s always better to have a policy in place that clearly defines procedures, responses and consequences for dilute specimens before you have to deal with this situation.

When A Negative Is Not A Negative

Tests can be returned from the lab as either negative dilute or positive dilute. A positive dilute test means that, despite the dilution of the sample, there was still enough of the drug present to be detected by the test. A positive dilute is still a positive. Your employee failed the drug test. Negative dilute specimens represent more of a grey area for employers. Some employers will require a follow up test while others may rely on random tests to catch any possible cheaters. Still others will accept the negative dilute as a negative test – in other words, the drug test is considered passed.

What Employers Can Do

DOT rules simultaneously give employers a lot of leeway and a lot of responsibility when it comes to the treatment of negative dilute specimens.

Employers may consider negative dilute specimens as negative and allow employees to still legally be able to work in safety sensitive positions. These rules also allow employers one additional test, but any decisions made not to hire an employee based on a negative dilute test must be purely based on the employer’s policy.

Employers can request a repeat of the urine test or can also change their retesting method to hair or saliva to avoid repeat dilution. But, requirements for retesting for negative dilute specimens should also be clearly defined in your drug testing policy prior to testing and they must be communicated to your employees. Bottom line: If you want to refuse a hire or provide any other consequences for a negative dilute, ensure you have a clear policy in place. This is equally true for non-DOT employers.

Busting The Myths

Despite the procedures in place to detect dilute specimens, some myths persist. Here are a few additional things you should know:

Dilution won’t guarantee a negative result

Whether the specimen is diluted innocently or on purpose, labs will immediately detect and report the dilution.

Taking additional creatinine won’t help

The internet is awash with advice for increasing creatinine levels to avoid getting caught by a diluted sample but neither taking creatinine nor eating red meat will increase the amount of creatinine in your urine.

Drinking excessive amounts of water won’t guarantee drugs will avoid detection

Not really. Nor will drinking vinegar or any other liquid. In one study, for example, marijuana use was still detected in 9.1% of dilute samples. Even if no drugs are detected the lab will still tag the specimen as dilute and additional testing may be ordered.