Specimen validity testing (SVT) is used to help ascertain whether the specimen being provided is actually urine (not substituted) and whether it has had any adulterants added to it. It is often used to ensure workplace safety when Point-of-care testing (POCT) is being done or to help design an informed regimen for a patient in rehabilitation.
What is it?
SVT testing looks for the most common masking agents that are used with urine drug testing as well as checking the specimen’s pH, specific gravity, and creatinine levels to help confirm whether it is a real urine specimen. Adulterant testing usually includes at least checks for oxidizing adulterants, nitrites, glutaraldehyde, and pyridinium chlorochromate.
Checking for dilution or substitution:
- pH – this determines the acidity/baseness of the urine sample. Normal urine is slightly acidic with a pH of ~4.5-9. Extremely alkaline (pH > 7.0) or acidic urine (pH <7.0) suggests that there has been tampering or adulteration of the sample.
- Creatinine – this is a normal excretion that our body deposits into our urine to remove it from our system from the metabolic work of our muscles. The level of this in our urine is fairly consistent for all humans, with <20 mg/dL indicating dilution. However, it must be noted that lower levels of creatinine can also be indicative of high fluid intake, renal failure, or other medical conditions.
- Specific Gravity – this is the determination of water density in relation to the mass of material in the sample ie. an indicator of dissolved particle concentration. Normal urine has a specific gravity ranging between 1.001 to 1.035.
Checking for adulterants:
- Oxidizing adulterant – this could be a chemical such as bleach, iodine etc. that could interfere with the detection of the drug and/or metabolites in the sample.
- Nitrites – these can appear naturally in urine due to infection, contamination or improper storage, but only up to levels of 3.6 mg/dL. If nitrite levels of >50 mg/dL are found this is generally considered an adulterated sample.
- Glutaraldehyde – this does not occur naturally in urine so if it is detected it is known to be an adulterated sample.
- Pyndinium Chlorochromate – this is not a normal constituent of urine and its presence in the specimen would indicate adulteration.
When do we use it?
It is not always appropriate to do specimen validity testing on a specimen, for example, a collector would NEVER do an SVT dip for a DOT, split specimen, laboratory collection. In fact, it would not be appropriate to do an SVT for a non-DOT or DOT straight-to-laboratory collection, as the laboratory does this testing themselves on every straight-to-lab sample they test. However, with a DOT it is specified by the regulatory body that no SVT should be done by the collector, whereas with a non-DOT collection there may not be any regulatory body advising of standards for collection procedures so it would be up to the employer/collector.
The most common time a collector would be doing specimen validity testing would be when completing a POCT test. A point-of-care test is the type where the collector analyzes the results right there in the office after obtaining the sample from the donor. In the case of POCT testing, the collector is often the only person who will be analyzing the specimen so it is up to them to do their due diligence to confirm it is not adulterated or substituted.
Once the collector has received the sample for the POCT test they will dip the SVT test strip into the sample for 1-2 seconds, tap off the excess urine and lay it flat, then read the results at 60 seconds. The results are read by comparing the colours on the test strip, for each specific parameter, to those found on the provided colour chart. The collector will then fill out what SVT they completed (and what the results they obtained) on the on-site testing form they are using.