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How To Read Drug Test Results: A Complete Guide

Illustration of a candidate's drug test results that shows negative and positive results.

For employers, drug testing is an important part of the hiring process and maintaining a safe, productive workplace. However, interpreting pre-employment drug test results can be challenging. With the right knowledge, employers can implement an ethical drug testing program that keeps workplaces safe while also upholding employee rights. 

This guide will explain what’s included in different employment drug testing panels, how the tests work, how to properly read and understand drug screen results, and what to consider if a candidate has a positive result. 

How To Read Drug Test Results

To best understand how to read drug test lab results, you also need to know what was included in the test. Each drug that is tested has a detection window, which is the length of time a drug remains in a person’s system and can be detected on a test. 

What does a negative drug test result mean?

A negative result indicates the lab found no presence of the drugs or metabolites tested for, or only found trace amounts below the designated cutoff threshold. This means the specimen “passed” the drug test. However, a negative result does not necessarily mean drug use hasn’t happened recently, since detection windows vary per substance. These detection windows range anywhere from a few hours (alcohol or heroin metabolite) to several days and weeks (benzodiazepines, PCP, and marijuana if used chronically).

What does a positive drug test result mean?

A positive drug test result means the lab detected the presence of a particular drug or metabolite at or above the cutoff concentration established for that substance. However, a positive result does not provide details like how much of the drug was taken, precisely when it was ingested, whether the person is still impaired, or if it was illicit versus prescription usage.

What information cannot be obtained from positive drug test results?

While a positive drug test confirms the presence of a substance, it does not provide context around:

  • How the drug entered the person’s system
  • The quantity consumed
  • Exact timing of ingestion (timing can be estimated based on detection windows)
  • Whether the person is currently under the influence (with the exception of a breathalyzer)
  • Potential substance abuse issues

What are the pre-employment drug screen cutoff levels? 

Cut-off levels on drug screens refer to the minimum drug concentration of a substance that will trigger a positive result. Understanding the cut-off level helps employers better interpret drug test results.

Lower cut-off thresholds make tests more sensitive, leading to a greater chance of false positives because of trace amounts of a substance (such as OTC painkillers or sleep aids). Higher cut-off thresholds decrease false positives but tend to allow more low-level drug use to go undetected.

For initial urine drug tests, common cut-off levels are 50 ng/mL for THC, 300 ng/mL for cocaine, and 2,000 ng/mL for amphetamines. Confirmation tests using the industry standard GC-MS test use lower 15/150/500 ng/mL cut-off levels to validate positive results. Knowledge of the cut-off levels chosen by your lab can help in proper analysis of the results.

What can cause a false-positive test result?

False positives occur when a substance in the specimen is chemically similar to the target substance. These “imposter” substances can be byproducts of prescription or over-the-counter medicines, such as allergy medications and sleep aids; dietary supplements, such as methylhexaneamine and synephrine; and even certain foods, such as coca tea and hemp seeds.

What Does Drug Testing Include?

Employment drug tests screen for a variety of legal and illicit substances depending on your workplace drug testing policy and the substances you wish to detect. These tests are offered in “panels,” which each screen for a specific number of substances. The most common panels are the 4-panel, 5-panel, 8-panel + MQL, and 10-panel drug tests, which include:

Drug test options

Drug Screen
4 Panel
5 Panel
8 Panel + MQL
10 Panel *

* Quick Test is available, however it excludes Methaqualone (MQL) and tests for Methamphetamine in its place.

Understanding the specific substances included in each panel allows for proper test preparation and accurate interpretation of results. Being aware of what is screened also enables candidates and employees to disclose any prescription medications ahead of time to avoid potential false positives.

How Are Drug Tests Performed? 5 Commons Types of Tests

There are several methods used to perform drug tests for employment purposes. Drug-testing laws vary from state-to-state, so certain testing methods may be prohibited in some states. The five most common samples include:

  • Urine: A urine drug test is the most frequently used method due to its combination of quick turnaround times, affordability, and wide detection windows for most substances. A urine sample can detect the presence of the drug within the detection window, but not the amount of drugs present in a person’s system—only that it is present. This means the employee or candidate wasn’t necessarily under the influence at the time of the test. 
  • Blood: A blood sample can directly measure the presence and concentration of drugs and metabolites in the bloodstream. This allows for quantitative analysis of substance levels. However, collection is more invasive than a urine sample and detection times may be shorter for some drugs.
  • Saliva: Saliva collected via oral swab offers a less invasive collection method. Saliva testing can detect very recent use of many drugs, with typical detection windows of 12-24 hours or less. This makes it ideal for reasonable suspicion or random drug testing. However, detection periods are shorter than urine overall.
  • Hair: Hair follicle drug tests provide the longest detection window of up to 90 days while also measuring the amount of drugs present at the time of the test. However, it cannot determine current impairment and is prohibited in some states. Hair testing also does not detect alcohol use.
  • Breath: The breath alcohol test uses a specialized breathalyzer device to measure current blood alcohol concentration (BAC) with a breath sample. This allows direct, immediate quantification of alcohol intoxication levels. A urine or saliva test can also detect alcohol use within prior detection windows.

What Are The Next Steps After Receiving Positive Drug Test Results?

When employers receive positive drug screen results from an employee or candidate, the appropriate next steps should be considered to maintain compliance with applicable laws. Before taking any action, you should review your company’s drug testing policy and follow those guidelines for next steps. 

Federally, the Civil Rights Act of 1964 prohibits employers from selecting individuals for drug testing based on protected classes, such as race, religion, or national origin. The Americans With Disabilities Act of 1990 prohibits discrimination against job candidates based on previous drug use or enrollment in a rehabilitation program. It also makes it illegal to single out people for drug testing because they appear to be under the influence. Behavior that seems to be substance-induced may be related to a disability, illness, or medical condition.

Drug screening is considered a type of employment background check and therefore the requirements of the federal Fair Credit Reporting Act (FCRA) also apply. These regulations ensure that candidates and employees have the right to review the results and dispute any errors and be made aware when those results are used in decisions about their employment.

Employment drug testing laws vary from state to state but can often guide next steps for a candidate or employee’s positive drug test result. For example, false positives may impact results and some states allow candidates to explain a positive test result within an allotted number of days. 

Get Employee Drug Testing Today

Interpreting drug test results and making fair employment decisions requires an understanding beyond a “positive” or “negative”. Partnering with a background check provider that offers drug testing can help streamline logistics, simplify results analysis, and support compliance.

GoodHire offers multiple drug screening options, each with review and verification from a Medical Review Officer to ensure the highest possible accuracy. We also offer other screening options to help you create a comprehensive background check program. Get started.  

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The resources provided here are for educational purposes only and do not constitute legal advice. We advise you to consult your own counsel if you have legal questions related to your specific practices and compliance with applicable laws.

About the Author

Lauren Woodyard headshot

As GoodHire’s Content Marketing Manager, Lauren develops resources to educate on employment screening best practices and compliance. She also writes about GoodHire’s platform and company news.