Drug testing is a standard procedure, typically performed using urine samples, that looks for the presence of drug metabolites—the byproducts created when the body breaks down a substance. Adulterants are chemical substances intentionally added to a biological sample after collection to compromise the integrity of the test results. This manipulation, known as in vitro adulteration, aims to produce a false-negative result. Laboratories have developed sophisticated measures to detect this practice.
What Adulterants Are and How They Function
Adulterants function by two primary mechanisms to undermine a drug test’s accuracy. The first involves altering the chemical matrix of the sample, which is the natural chemical environment of the urine. Normal urine has expected ranges for physical properties like temperature, pH level, and specific gravity; deviation outside these parameters can cause the sample to be rejected as invalid. For example, adding water dilutes the sample, lowering its specific gravity and the concentration of drug metabolites below the test’s cutoff threshold.
The second mechanism is chemical interference with the immunoassay. Immunoassays rely on antibodies binding to drug metabolites to register a positive result. Certain chemicals interfere with this binding process or chemically destroy the metabolite itself, effectively masking the drug’s presence and leading to a false-negative screen.
Common Chemical Classes Used to Interfere with Tests
A major class of adulterants includes strong oxidizing agents. Common household items like bleach and hydrogen peroxide fall into this category, as do commercial products containing chemicals like potassium nitrite or pyridinium chlorochromate (PCC). Nitrites, for instance, oxidize the major cannabinoid metabolite, THC-COOH, rendering it undetectable by testing methods. PCC is another potent oxidant that can reduce the detection of substances like morphine and marijuana metabolites.
Another common strategy involves using strong acids or bases to push the sample’s pH outside the acceptable physiological range. Normal urine pH typically falls between 4.5 and 8.0. Adulterants like vinegar or lemon juice introduce excessive acidity, while substances like drain cleaner or baking soda create extreme alkalinity. When the pH is shifted too far from the normal range, it compromises the stability and integrity of the drug metabolites and the testing reagents themselves.
Glutaraldehyde represents a separate chemical class that acts as a non-oxidizing masking agent. This compound is used to interfere with enzyme-mediated immunoassays. Glutaraldehyde disrupts the function of the enzyme used in the assay, which prevents the proper signal from being generated when a drug metabolite is present. Although glutaraldehyde is not naturally found in urine, it is included in several commercially marketed adulteration agents.
Laboratory Methods for Identifying Tampered Samples
Laboratories employ comprehensive validity testing. A fundamental physical check involves measuring the temperature of the sample immediately after collection, which should be within a narrow range, typically between 32 and 38 degrees Celsius; a temperature outside this range suggests the sample may have been substituted with clean or synthetic urine. Specific Gravity (SG) is also measured to detect dilution, where an SG reading below the acceptable limit indicates that water was added or excessively consumed.
Creatinine measurement is a highly reliable marker for dilution, as this waste product is excreted in urine at a relatively constant rate. A creatinine concentration below 20 mg/dL is generally considered indicative of a dilute sample. If the sample is found to be dilute, it is often flagged as invalid or rejected for testing.
Laboratories also run specific chemical tests for the presence of the common adulterant classes. Test strips or automated analyzers are used to screen for high levels of nitrites, oxidants, and glutaraldehyde, none of which should be present. Additionally, the pH level is tested, and a reading that is extremely acidic or alkaline will cause the sample to be reported as adulterated.