For employers who use drug testing as part of their Drug-Free Workplace or safety programs, it’s important that screening results be accurate. Part of ensuring accuracy is ensuring the validity of submitted samples, including catching the common cheating method of diluting the urine sample.(Learn more in "Top 3 Ways Employees Try to Cheat Drug Testing".)

Why Employers Need Drug Tests to be Accurate

  • Help avoid hiring candidates who may present a risk to the workplace
  • Identify and assist employees who may be abusing illegal substances
  • Maintain a safe and productive work environment
  • Comply with DOT Mandatory Guidelines for Workplace Drug Testing
  • Reduce litigation for false positive results and subsequent discipline or termination

Drug Test Procedure Overview

The standard method of drug testing is to ask the candidate or employee to provide a urine specimen, according to company policies. The sample is obtained in a designated private setting, with trained medical personnel overseeing the procedure:

  1. The person being tested shows a photo I.D.
  2. Purse, bag, coats, and other belongings are put in a secure place before starting. Pockets are also emptied.
  3. A sealed and labeled specimen cup is given to the person being tested.
  4. The person being tested receives instructions on how to clean the genital area before urinating into the cup. Disposable moist towelettes are provided.
  5. In a designated restroom, the person urinates into the cup, places the lid back on, and returns it to the collector.
  6. The temperature of the sample is immediately taken, to be sure that it is in the normal range of body temperature.
  7. The person being tested witnesses the sample as it is placed in a sealed specimen bag and packaged for the lab.
  8. The sample is sent to the testing laboratory, where it will be divided into two parts (split specimen): One for initial testing, and a second for possible confirmatory testing and an archive sample. (Learn more in "Three Types of Drug Testing: What Employers Should Know About Lab Testing, POCT, and Express to Lab Testing.")

Diluted Sample Cheating

Although the testing process is straightforward and designed for verifiable chain-of-custody documentation, people will still sometimes try to cheat. The most common method of cheating is to dilute the urine in an attempt to reduce the concentration of drug metabolites that are present. A quick “beat a drug screen” internet search brings over 4.5 million results. Some websites, such as marijuana.com, go so far as to provide instructions on how to dilute urine for a drug screen, as well as other ways to attempt to beat the system.

One such suggested cheating method is dilution and instructs people to drink at least a gallon of water before urinating. In addition to not being a foolproof way to cheat a drug test, overhydration can be life threatening. Often, the person being tested hopes for:

  1. A sample that is dilute enough to create a negative result from no detected drug metabolites or a level low enough to be below the cut off value. (Learn more in "Drug Detection Cutoffs: What You Need to Know".)
  2. An inconclusive result that requires a second screening. This allows for more time for drug metabolites to naturally leave the body.

Finding Dilute Specimens

A dilute specimen is quickly determined in the laboratory setting. The first analysis is to determine the creatinine level of the specimen. Creatinine is the waste byproduct of normal muscle movement that is filtered out by the kidneys, and eliminated through the urine. A normal creatinine level is 88-128 mL/min for females and 97-137 mL/min for males. When a specimen is dilute, the creatinine level is <20mL/min.

The second analysis for all urine samples is to measure the specific gravity level, which is the density of urine compared to the density of water (1.0000). Since urine is heavier, the normal range is 1.0020-1.0030. However, if the sample has been diluted, the result will be out of range.

Another quick dilution check is urine color. Colorless or extremely pale urine is usually the result of overhydration.

What Happens if a Dilute Specimen is Found

When the Medical Review Officer (MRO) receives a dilute specimen result, there are several actions the MRO can take. The Substance Abuse and Mental Health Services Administration (SAMHSA) has a comprehensive Medical Officer Review Manual that provides clear guidelines for dealing with dilute specimens.

The DOT Rule (Learn more in "DOT vs. Non DOT Testing: What's the Difference?") that applies to dilute samples (§40.197) states that when the MRO informs the employer of a dilute specimen result:

  • If the test is positive-dilute, it is considered valid. Company or DOT policies regarding a positive test result are followed. While the sample was dilute, there was still enough of the drug present to be detected at designated levels.
  • If the test is negative-dilute, follow the MRO’s instructions:
    • If the MRO directs the employer to obtain a new sample, taken under direct observation (a same-gender technician witnesses the collection), do it immediately. The MRO will request the recollection when the creatinine level result was ≥ 2 mg/dL, but ≤ 5 mg/dL.
    • If the creatinine level result was ≤ 5 mg/dL, the employer can decide if another sample should be collected and tested. If the employer chooses to repeat the collection, it is not to be done under direct observation.
    • The employee should be given as little advance notice as possible to go to the collection site.
    • Only one recollection is allowed. The second results are considered final and the results that will be recorded on the employee’s record.
  • All employees must be treated equally. An employer may not retest some employees, but not others. However, the employer may have different policies for certain situations, such as job candidate testing.
  • The employer must notify employees of testing policies and consequences prior to starting a drug screening program.
  • If an employee declines to take an initial drug test as directed or to provide a second sample, the employer can proceed according to company policies and DOT regulations on refusal to test.

Because the DOT permits an employer to accept a negative-dilute sample as valid, the company has several choices:

  1. Accept the results and do nothing. There is a risk that person being tested is a substance abuser and will later fail a random or post-accident drug screen.
  2. Initiate a firm policy of retesting all negative-dilute results. This treats all results and employees the same way, although it costs more.
  3. Change retesting methods to obtaining a hair or saliva sample. This reduces the chance of a second dilute sample, but can be expensive. (Learn more in "Oral Fluid, Urine, and Hair Testing: What's the Difference?")

Employers should anticipate possible drug screen situations that include dilute results. By establishing policies regarding drug testing, (Learn more in "Drug Test Types: 5, 7, and 12 Panel Urine Screening Differences and Reasons to Use".) including the procedure for positive-dilute and negative-dilute test results, an employer can inform all prospective and current employees of the process and consequences of a dilute specimen.