Invalid Drug Test

Definition - What does Invalid Drug Test mean?

An invalid drug test is the outcome of a drug test for a urine sample that contains an endogenous substance at abnormal concentrations, has abnormal physical characteristics, contains an unknown interfering substance, or an unknown contaminant that prevents the laboratory from obtaining a suitable valid result on the test.

WorkplaceTesting explains Invalid Drug Test

In case a specimen (urine) is found to have an adulterant/interfering substance that prevents the recognition of the metabolite or drug in the confirmation test and there is a substantial decrease, or no recovery, of the internal standard even after several attempts of extractions, the lab may consult with the Medical Review Officer (MRO). The specimen will then be sent to another lab that is certified by the Health and Human Services (HHS) department that is capable of carrying out scientifically approved tests of validity to figure out what the adulterant is. Finally, if this procedure also fails to shed light on the interfering substance, then the second lab will also report an invalid drug test.

A laboratory will report an invalid drug test the moment any of the following conditions take place:

  • An unidentified substance interfered with the validation test
  • Valid preliminary drug test results can’t be obtained; for example, a lab fails to obtain a valid preliminary test result for every preliminary test and is unable to determine specifically what the cause is.
  • Temperature or PH is out of range
  • The sample is not suitable for testing; for instance, the physical appearance of the specimen is not acceptable and may have an effect on the analysis of the sample.


The Medical Review Officer (MRO) then has to question the donor of the specimen to find out whether the donor can give a credible why the sample couldn’t be properly tested by the lab. For example, certain health and food supplements, prescription medications, or medical illnesses.

Share this:

Connect with us

Email Newsletter

Join thousands of employment testing and employee wellness professionals.