A result that often confuses clients is the Negative Dilute, whether it be in a DOT or non-DOT environment. The most common concern is, should this be considered a TRUE negative, or does it require a retest?

The first place to look for this information is in the letter comments of the MRO report that you receive. These comments, located at the bottom of the report, below the list of metabolites and confirmed results, will indicate if there are any further actions required based on the confirmed results.

Dilutes fall into two main categories, those that do NOT require a retest, and those which do. These two categories are defined by the same parameters for both the N-DOT and DOT environments, and you will find that the letter comments in both environments are usually the same. A dilute specimen is one that has a higher than average water content, which could be for various reasons, ie. the donor drank a lot of water in preparation for their test, or due to medications, or because they are trying to dilute the specimen to mask drug use.

Whether or not the MRO requires a dilute specimen to be retested is based on the levels of the Specific Gravity, and the Creatinine, two parameters which are tested on every specimen to confirm their validity. If you’re interested in understanding more about what Specimen Validity Testing is, it is explained here.

The chart below indicates the levels that the laboratory and the MRO use to determine whether the dilute specimen is acceptable or requires a retest under direct observation. This is based on the levels for the two parameters, one set indicating that the sample is dilute within an acceptable range (with a higher concentration of water to uric acid than normal, acceptable here meaning not so extreme as to make it an obvious attempt to adulterate). A dilute specimen within the acceptable range, that which does NOT require an observed retest, can be physiologically normal, however may raise the suspicion of the employer. This is why for the dilute specimen in the acceptable range the letter comments will indicate that there is no requirement for a retest. The letter comments state that it is up to the employer (meaning, their policy) as to whether or not they require retests for this level of dilute.

This determination of requiring, or not requiring, a recollection stands for a DOT or N-DOT specimen, the parameters for defining the two, and the requirements for a retest are the same in the two environments. The DOT considers a Negative Dilute (in the acceptable range) to be a Negative result, meaning there is NO NEED to do a retest, and those results fulfill the need for a Negative test. However, if an employer finds that dilutes make them suspicious, and wants them retested, please make sure this is in the policy and is applied the SAME to ALL Negative Dilute results. Do not choose randomly which Negative Dilutes you think need a retest, if you retest them, you must have that be your policy with ALL of them.

As you can see in the chart, if the specimen is in the more extreme range of dilution than the letter comments will let the employer know that they need to retest that donor immediately under DIRECT OBSERVATION. In this range the laboratory has deemed this result so far out of the range of normal that it is under suspicion that substitution took place, requiring an immediate recollection under direct observation. That means if it is deemed dilute in the NOT acceptable range, it is NOT considered a Negative by the DOT, which is why an immediate recollection under direct observation is required. In keeping with this, in the DOT environment, if a donor refuses to complete a required direct observation recollection due to levels of dilution, this would be deemed a refusal to test.

Under the DOT regulations there are further value parameters which the laboratory has which could deem an extremely dilute specimen either a Substituted OR Invalid result. These are situations in which the values are so far off from what is physiologically possible that the result would not even indicate that it was dilute, it would simply be resulted to the MRO as Substituted, or Invalid. The MRO would then have an interview with the donor, and then confirm the result as either a Refusal to Test, or Cancelled with a requirement for immediate recollection under Direct Observation.