What Does an “Inconclusive” Drug Test Result Mean?
Drug testing is a standard tool for employers, legal authorities, and healthcare providers. Most tests provide clear results: either negative (no drugs detected) or positive (drugs detected). However, sometimes the result comes back as “inconclusive”. This can be confusing and stressful for the person tested, especially if employment, legal matters, or probation compliance is involved.
An inconclusive drug test result does not mean a person is positive or negative for drugs. Instead, it indicates that the test could not definitively confirm or rule out the presence of drugs. Understanding why a result is inconclusive, how labs handle it, and what steps to take next is crucial for both individuals and employers.
This article explains what an inconclusive drug test result means, common causes, how laboratories address it, and how to respond appropriately.
What Does “Inconclusive” Mean in Drug Testing?
In drug testing, “inconclusive” (sometimes reported as “invalid”, “equivocal”, or “borderline”) means:
- The laboratory could not definitively detect or rule out the presence of drugs.
- The sample may have been compromised, diluted, or interfered with.
- The levels of the drug were near the cutoff threshold, making results uncertain.
Unlike a positive result, an inconclusive result does not confirm drug use. However, it usually requires further investigation or retesting.
Common Causes of Inconclusive Drug Test Results
Several factors can lead to an inconclusive result:
1. Low Drug Concentration
- Drugs may be present in the body but at levels too low to detect.
- Early use, small doses, or infrequent use may not produce measurable results.
- Lab instruments may not detect substances below a specific cutoff concentration.
2. Diluted or Contaminated Sample
- Drinking excessive water before a urine test can dilute drug concentration.
- Contaminants like soap, food, or chemicals may interfere with results.
- Inadequate sample collection can also cause inconclusive outcomes.
3. Interfering Substances
Certain legal substances, supplements, or medications may interfere with screening tests:
- Over-the-counter cold medications
- Prescription drugs
- Dietary supplements
This interference can cause false positives or inconclusive readings.
4. Laboratory or Equipment Errors
- Malfunctioning instruments
- Improper sample handling
- Errors in labeling or storage
Such procedural errors may lead to a test being flagged as inconclusive.
5. Expired or Improper Reagents
- Chemicals used in immunoassay screening may degrade over time.
- Using outdated reagents can prevent accurate detection.
6. Sample Degradation
- Urine, saliva, or blood samples can degrade if not stored correctly.
- Temperature fluctuations, delays, or contamination can make results unreliable.
Types of Tests That Can Return Inconclusive Results
Inconclusive results can occur with various drug test types:
- Urine drug tests – most common
- Saliva (oral fluid) tests – affected by eating, drinking, or contamination
- Hair follicle tests – rare, but can occur with insufficient hair
- Blood tests – uncommon, usually due to low drug levels or lab error
What Happens After an Inconclusive Drug Test?
When a test is inconclusive, laboratories and employers typically take the following steps:
Confirmatory Testing
Samples may undergo GC/MS (Gas Chromatography–Mass Spectrometry) or LC-MS/MS testing to clarify results.
Request a Retest
Individuals may be asked to provide a new sample.
Check Sample Integrity
Labs ensure the chain of custody is intact.
Any signs of tampering or contamination are reviewed.
Inconclusive vs. Negative vs. Positive Results
| Result Type | Meaning |
|---|---|
| Negative | No drugs detected; test passed |
| Positive | Drugs detected above cutoff; test failed |
| Inconclusive | Unable to determine; retesting or further review needed |
Inconclusive results are not considered a “fail” but cannot be ignored.
Can an Inconclusive Result Affect Employment or Legal Status?
Yes, it can, depending on the situation:
- Employment: Employers may request retesting or follow internal policies for inconclusive results.
- Legal Cases: Courts, probation offices, or regulatory agencies may require a new test.
- Safety-Sensitive Jobs: Positions like commercial drivers may have strict rules requiring definitive results.
Transparency and timely communication are critical in these situations.
How to Handle an Inconclusive Drug Test Result
For Employees or Interns
Notify the Testing Facility or Employer
Ask for clarification and instructions.Request Retesting
Provide a new sample if allowed.Document Everything
Keep records of communications and testing dates.Disclose Medications or Supplements
Inform labs about any prescription or over-the-counter substances that may affect the test.
For Employers
Follow Policy Consistently
Treat inconclusive results according to company drug testing policies.Verify Chain of Custody
Ensure proper handling and storage of samples.Use Confirmatory Testing
Immunoassay screening alone is not enough for conclusive results.Communicate Clearly
Inform the individual of the result and next steps in writing.
Tips to Avoid Inconclusive Results
- Hydrate responsibly: Avoid excessive water intake before testing.
- Follow test instructions carefully: Especially fasting or medication rules.
- Avoid contamination: Do not use soaps, chemicals, or foreign substances before providing a sample.
- Disclose all substances: Vitamins, supplements, and prescription drugs may matter.
Frequently Asked Questions
Q: Does inconclusive mean I failed the test?
A: No. Inconclusive results mean the test could not definitively detect or rule out drugs. Follow-up testing is usually required.
Q: Can an inconclusive result be challenged?
A: Yes. Request confirmatory testing or review lab procedures.
Q: How long does it take to resolve an inconclusive test?
A: It depends on lab turnaround and retesting requirements, usually a few days to a week.
Summary: What Does an “Inconclusive” Drug Test Result Mean?
An inconclusive drug test result indicates that the test could not definitively detect or rule out drugs. Causes include low drug levels, diluted or contaminated samples, interfering substances, or laboratory errors. Confirmatory testing or retesting is usually required. Inconclusive results are not a positive test but do require proper handling by both the individual and the employer.
Final Thoughts
Understanding inconclusive drug test results helps reduce confusion and stress for both employees and employers. Proper procedures, clear communication, and timely retesting ensure that inconclusive results do not unfairly impact careers, legal matters, or compliance requirements.
