Specimen Validity Testing

specimen validity testing

Urine drug testing relies on the analysis of a valid urine specimen. Without a valid urine specimen, the drug test is pointless. While not common, specimen tampering, substitution and adulteration are realities. It is essential to verify that the specimen submitted is valid.

In addition to performing a drug test, STL can also verify that the sample received is urine (which it may not always be), free from adulteration and is of sufficient concentration to render a valid drug test result. We conduct validity tests on urine specimens submitted to our laboratory to ensure that the specimen is valid for urine drug testing. Specimen validity tests include creatinine, specific gravity, pH and oxidant testing.


Creatinine is a waste product produced by the body and excreted in the urine. Our laboratory has the capability of determining a quantitative level of creatinine in a urine sample. A normal urine sample has a creatinine level greater than or equal to 20 mg/dL. If no creatinine is present, the sample submitted is not urine. Common substitutes for urine are apple juice and tea.

Specific Gravity

Specific gravity is an indication of the amount of solid particles dissolved in a urine sample. We can determine a quantitative level of specific gravity in a urine sample. A normal urine sample has a specific gravity of greater than or equal to 1.003.

If a urine sample has a creatinine value less than 20 mg/dLand a specific gravity less than 1.003, then the sample is considered dilute and will be reported as such. This dilution can come from either drinking large volumes of liquid before providing a urine sample, or pouring something into the urine cup at the time of collection. Either way, the sample is considered dilute, and may not provide a proper evaluation of drug use by the donor/patient. We advise re-testing if a sample appears to have been diluted.

Specimen Adulteration

Specimen tampering is a deliberate malicious attempt to subvert the drug test and is an ongoing concern for urine drug testing. There are several products which, when added to the urine specimen, either degrade the drug or interfere with the testing protocol, or both. Some of these products are found around the house (bleach and detergent, for example) and many are purchased commercially. Some of these products shift the pH of a urine specimen. Shifting the pH of a specimen may degrade drugs present in the sample or may interfere with the analysis of a specimen, or both. Some adulteration products are classified as oxidants. Oxidants present in a urine specimen may degrade drug present or may interfere with the analysis of a specimen, or both.


A pH test determines the degree of acidity or alkalinity of a urine sample. A normal urine specimen has a pH between 5 and 8. Our acceptable pH range runs from 3.0 to 10.9. This expanded range allows for medical conditions and other factors (such as bacterial activity) which may alter the pH of a urine sample without any malicious intent on the part of the donor. Any sample with an abnormal pH outside of our range of 3.0to 10.9 is an adulterated sample, meaning something has been added to the urine sample after voiding for the purpose of tampering with the drug testing process.

Bleach and ammonia, for example, will produce a basic pH (11 or greater). Lemon juice and vinegar can produce an acidic pH (3 or lower). Specimens with pH values less than 3 or greater than or equal to 11 will be reported as adulterated. A specimen reported as adulterated should be interpreted with the same severity as a positive drug test result.

Oxidant testing

While it is impossible to test for all possible adulterants, most fall into the category of oxidizing agents. A general oxidant screen test is designed to identify specimens tampered with oxidizing agents. Specimens positive by this methodology will be reported as "Invalid: possible oxidant activity".