Specimen validity testing (SVT) is a set of laboratory tests performed on every drug test specimen to detect adulteration, substitution, or excessive dilution. SVT measures creatinine concentration, specific gravity, pH, and the presence of oxidizing adulterants. A specimen with creatinine < 2 mg/dL and specific gravity < 1.0010 is "substituted" — treated as a refusal to test under DOT rules. A specimen with abnormal pH (< 3 or > 11) or oxidizing agents is "invalid." Under 49 CFR Part 40, SVT is mandatory for all DOT drug tests. Non-DOT employers increasingly include SVT as best practice.