When a drug test result is returned, the laboratory and the Medical Review Officer (MRO) use standardized codes to communicate the status of the specimen and the final outcome of the screening. These codes are important in regulatory environments, such as federal workplace testing, where precision is required for compliance. The designation ‘XM’ can appear on a report, sometimes indicating a panel type, but when it relates to the result status, it signals an issue that prevents the test from being reported as positive or negative. This status, often labeled as a “Canceled Test” or “Invalid Result,” immediately triggers a specific protocol overseen by a licensed physician.
The Direct Meaning of ‘XM’
The designation ‘XM’ on a drug test report has two common interpretations. In commercial labs, ‘XM’ frequently serves as an abbreviation for “eXcludes Marijuana,” indicating the test panel omits THC screening. However, when ‘XM’ is used to describe the final status of a specimen in a regulated environment, it refers to a “Canceled Test” that was initially reported by the laboratory as an “Invalid Result.”
A “Canceled Test” means the laboratory was unable to establish a clear result—positive, negative, substituted, or adulterated—due to a fatal flaw in the collection or testing process. The test is legally rendered null and void, meaning the result cannot be used against the donor, nor can it be used to certify a negative result for employment purposes. The MRO is the only party authorized to officially cancel a regulated drug test after reviewing an invalid laboratory finding.
Reasons for the ‘XM’ Designation
The ‘XM’ designation, or Canceled Test status, is caused by fundamental problems that compromise the integrity of the specimen or the testing procedure. These reasons fall into two broad categories: procedural errors and specimen validity issues.
Procedural errors, often called “fatal flaws,” relate to mistakes in the chain of custody. Examples include broken seals, missing donor signatures on the custody and control form, or the lab rejecting the specimen due to an uncorrectable documentation error.
Specimen validity issues are discovered during laboratory analysis. These include findings of abnormal pH levels or the presence of substances that interfere with the initial immunoassay screening.
A common issue is a specimen with extreme specific gravity or creatinine levels, indicating an attempt at substitution or dilution to mask drug use. When the lab reports an “Invalid Result” due to these chemical anomalies, the MRO must investigate before declaring the test officially canceled.
The Role of the Medical Review Officer
The Medical Review Officer (MRO) is a licensed physician who acts as an independent “gatekeeper” between the laboratory and the employer. When a test is reported as an Invalid Result, the MRO reviews the laboratory data and all collection documentation to determine the final status. This physician ensures the accuracy and integrity of the entire drug testing process according to federal standards, such as those established by the Department of Transportation (DOT).
The MRO will attempt to contact the donor to discuss a potential medical explanation for an invalid result, such as a prescription medication that may have interfered with the immunoassay. If the donor provides an acceptable medical explanation, the MRO cancels the test and reports it as such to the employer. If no medical explanation is offered, or if the MRO suspects tampering, the test is still canceled, but a retest is usually required.
Required Actions Following an ‘XM’ Result
The final “Canceled Test” status reported by the MRO dictates the next steps for the donor and the employer. A canceled test is explicitly defined as neither a positive nor a negative result.
The employer cannot impose consequences associated with a positive test, but the donor also cannot use it to fulfill a requirement for a negative result. This is relevant for pre-employment or return-to-duty testing, where a verified negative result is mandatory before an employee can begin safety-sensitive duties.
If the original test was required for employment clearance, a canceled test almost always necessitates an immediate retest, which is a new collection process. The MRO will instruct the employer whether this retest should be a standard collection or a directly observed collection. Direct observation is required if the invalid result suggested suspected tampering with the original specimen.