Can Diluted Urine Give a False Negative Drug Test?

Employers often use urine drug tests to screen for drug use in the workplace. However, diluted urine samples can sometimes lead to ambiguous or false negative results. In this blog post, we’ll explore what diluted urine is, how it can impact drug test results, common causes, and tips for preventing diluted samples.

What is Diluted Urine?

Diluted urine is a urine sample that contains higher amounts of water than normal. Typical urine concentration ranges from 1.002 to 1.030 in specific gravity. Diluted urine has a specific gravity of 1.001 to 1.003. The creatinine level, which indicates concentration, is also reduced in diluted samples to less than 20 mg/dL (compared to a normal range of 20-350 mg/dL). The higher water content makes it difficult to accurately detect the presence of drugs.

Impact on Drug Test Results

The excess water in diluted urine samples can lead to:

  • False negatives – The drugs may be too diluted to be detected by the test, even if the employee is using drugs. This allows drug users to go unidentified.
  • Ambiguous results – The test may detect some traces of drugs, but not enough to return a definitive positive result. This makes it unclear if drug use has actually occurred.
  • Invalid results – The urine concentration is so low that the sample is considered invalid and the test must be retaken.

Common Causes of Diluted Urine

There are several reasons why an employee may unintentionally or intentionally submit a diluted urine sample:

  • Excessive hydration – Drinking large volumes of water before the test dilutes the urine.
  • Diuretics – Medications and other products that increase urination can dilute the urine. Examples include caffeine, herbal teas, and blood pressure drugs.
  • Kidney dysfunction – Kidney disorders can prevent the organs from concentrating urine properly.
  • Attempts to cheat drug test – Some employees may deliberately drink excessive fluids or use diuretics to try to pass a drug test when they are taking drugs.

Preventing Diluted Urine Samples

As an employer, you can take the following steps to reduce the chances of receiving a diluted urine sample:

  • Don’t allow excess water intake right before testing
  • Test earlier in the day before employees drink large volumes of fluids
  • Educate employees on how dilution can impact results
  • Use random test scheduling to prevent tampering
  • Follow guidelines for identifying and managing diluted specimens
  • Retest any diluted samples for validity

Diluted urine samples can compromise the accuracy of workplace drug tests. However, by understanding what causes dilution and implementing procedures to prevent it, employers can increase their chances of obtaining a valid drug test result. With the right policies in place, diluted urine will not lead to false negative results.

Photo by Anthony Cunningham for Zoom Testing

Zoom Testing is a leading UK drug testing company and a supplier of Drug Test Kits.

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