Specimen validity testing (SVT) checks whether a urine sample is genuine, adequately concentrated, and free of adulterants before its drug results are trusted. Dilution, substitution, and adulteration can all push a true positive below the cutoff, so an invalid specimen can make a patient who is using drugs appear negative.1
When high-volume drug testing expanded in the 1990s, dilute samples reported as negative were shown to contain drugs below the cutoff at much higher rates than normal samples, which led federal programs to mandate SVT and standardize its methods.1 Adulterant products such as nitrite, PCC, glutaraldehyde, and peroxide remain marketed online and in shops to defeat testing.2
Beyond confirming integrity, SVT supports interpretation. Urinary pH affects excretion of drugs such as methadone, phenobarbital, and amphetamines, so pH shifts can explain fluctuating urinary levels. Creatinine can normalize a patient's drug and metabolite concentrations across serial samples to compare results over time.3 Routine SVT may not detect all synthetic urines.4
| Validity Marker | What Can Cause an Abnormal Result |
|---|---|
| Creatinine >20 mg/dL |
Dilution: excessive fluid intake near collection (~3 quarts within hours, especially with a diuretic); water added to the specimen. Substitution: very low (<2 mg/dL) or absent creatinine is not physiologically possible; the specimen is not human urine. Benign: low muscle mass; renal disease; elevated storage temperature can lower measured creatinine, mimicking dilution. |
| Specific Gravity 1.003–1.035 |
Dilution: <1.003 with low creatinine (over-hydration or added water); <1.001 approximates water. Adulteration: added salt (sodium chloride) raises specific gravity and can cause false-negative immunoassay. Substitution: >1.020 with low creatinine suggests a non-urine liquid (e.g., juice). Benign: high specific gravity with elevated creatinine is concentrated urine from dehydration. |
| Oxidant <200 mcg/mL |
Adulteration: nitrites (Klear, Whizzies), PCC (Urine Luck), chromium(VI), bleach and other halogens, peroxide (Stealth), glutaraldehyde (Urine Aid). Benign / other: urinary tract infection (values near 200 mcg/mL); blood contamination; dietary nitrite (cured meats; celery, spinach, beets); nitrate-rich well water; nitrate medications. |
| pH 4.5–9.5 |
Adulteration: acidic or alkaline adulterants (abnormally high or low pH). Benign (acidic): uncontrolled diabetes or DKA, ketogenic or high-protein diet, SGLT2 inhibitors, systemic acidosis. Benign (alkaline): natural rise toward 9.5 with prolonged storage. |
Markers are interpreted as a whole, alongside the laboratory's physical examination (color, odor, foreign objects) and specimen temperature at collection. No single marker confirms tampering on its own. Some adulterants, such as surfactants and detergents, are not reliably detected by these four tests and may require a dedicated assay or direct observation.