Specimen Validity Testing (SVT) is a laboratory quality control process designed to confirm that a biological sample, most commonly urine, is consistent with normal human body fluid. This procedure is performed simultaneously with the drug screen to ensure the specimen’s integrity before the actual drug test results are finalized. The goal of SVT is to detect attempts to tamper with the sample, such as by dilution, substitution, or the addition of foreign chemicals. By confirming a specimen is authentic, the testing process provides reliable results that accurately reflect the donor’s physiological state.
The Necessity of Specimen Integrity
The accuracy of any drug test hinges entirely on the integrity of the collected sample. Specimen Validity Testing serves as a safeguard against manipulation, which could otherwise lead to inaccurate or misleading drug test results. Without this verification step, the primary test results could be easily compromised by simple acts like adding household products to the sample or drinking excessive amounts of water immediately prior to collection. This verification process ensures fairness and reliability for all parties involved, whether in a workplace, medical, or legal setting. Regulatory bodies in certain safety-sensitive industries mandate SVT to maintain high standards of accuracy and compliance.
Core Indicators of Specimen Validity
Laboratories rely on three primary scientific parameters to determine a specimen’s validity. The concentration of creatinine, a waste product of muscle metabolism, is measured first. A normal human urine specimen is expected to have a creatinine level at or above 20 milligrams per deciliter (mg/dL). Low creatinine levels, particularly below 5 mg/dL, strongly suggest the individual consumed large amounts of fluid or added water directly to the sample to dilute the concentration of any drug metabolites present.
Specific Gravity (SG) indicates the concentration of dissolved particles in the urine relative to water. Normal human urine typically has an SG ranging from approximately 1.003 to 1.030. Low specific gravity values, especially when paired with low creatinine, point toward dilution, where the concentration of natural constituents is too low. Conversely, an SG that is abnormally high may suggest that foreign substances or contaminants were added to the specimen to mask tampering.
The acidity or alkalinity of the sample is measured by its pH level, which must fall within a narrow physiological range, typically between 4.5 and 9.0. Deviations from this range indicate that an acidic or basic substance may have been introduced into the specimen. Common household chemicals like vinegar, bleach, or soap are strong acids or bases that can dramatically alter the pH, potentially interfering with the drug detection assays. Testing for oxidizing adulterants, such as nitrites or chromates, is also performed, as these chemicals are often added to destroy or mask drug metabolites.
Defining Invalid Specimen Categories
The results of Specimen Validity Testing lead to four distinct classifications for a sample that fails to meet the criteria for normal human urine. A dilute specimen is characterized by creatinine levels between 2 and 20 mg/dL and a specific gravity between 1.0010 and 1.0030. This often results from excessive fluid intake, which lowers the concentration of all components, making drug detection more difficult.
A far more severe finding is a substituted specimen, reported when the creatinine concentration is near zero (less than 2 mg/dL) and the specific gravity is extremely low (at or below 1.0010). This combination indicates the sample is not consistent with human urine and suggests it was replaced with water, synthetic urine, or another liquid. A third category is the adulterated specimen, which contains a substance not normally found in urine or has an endogenous substance, like high pH, at a non-physiological concentration. This classification is used when a foreign chemical, such as bleach or glutaraldehyde, is identified, or when the pH is outside the accepted range of 4.0 to 11.0.
Finally, an invalid result is reported when the laboratory cannot establish a definitively negative, positive, adulterated, or substituted result. This classification is used when the sample has an abnormal physical characteristic or contains an unidentified interfering substance that prevents the completion of the test. While an invalid result does not necessarily prove tampering, it indicates the sample’s components are so inconsistent that the reliability of the drug test results is compromised.
The Consequences of an Invalid Result
The classification determined by SVT dictates the procedural next steps for the donor and the organization requesting the test. When a specimen is reported as substituted or adulterated, the Medical Review Officer (MRO) typically treats the result as a refusal to test. This outcome is equivalent to a positive drug test in many regulated settings and can lead to immediate disciplinary action, including termination of employment. The rationale is that the individual intentionally compromised the integrity of the testing process.
A dilute or invalid result, however, often requires a different course of action that is less punitive. In most cases, a specimen classified as dilute or invalid requires a mandatory retest, which is often conducted under direct observation to prevent any further attempts at tampering. This ensures that the donor provides an authentic sample for a definitive result.