Benzoylecgonine (BZE) is the main inactive byproduct created when the body processes cocaine. Cocaine is quickly broken down, but BZE remains stable and is the substance measured in standard drug screenings, particularly urine tests, to determine use. The concentration of BZE is measured in nanograms per milliliter (ng/mL) and provides a quantifiable marker of exposure.
The Role of Benzoylecgonine in Drug Screening
Drug testing panels focus on BZE because the parent drug, cocaine, is metabolized almost immediately after entering the bloodstream, possessing a very short half-life of about 1.5 hours. This rapid breakdown means cocaine is only detectable for a few hours in most biological samples. Liver enzymes convert cocaine into BZE, which is pharmacologically inactive.
The BZE metabolite has a much longer half-life, typically ranging from 5.5 to 12 hours. This extended presence in the body makes BZE an effective target for testing, providing a wider window of detection to confirm cocaine use that occurred days before the sample was collected.
Defining the Cut-Off Thresholds
The interpretation of BZE levels revolves around established cut-off concentrations set by regulatory bodies, such as those governing federal workplace drug testing. These standards use two tiers of numerical thresholds to ensure accuracy. The initial screen, often an immunoassay, typically uses a cut-off of 150 ng/mL to separate negative samples from those requiring further analysis.
Any sample screening at or above 150 ng/mL proceeds to a precise confirmatory test using Gas Chromatography/Mass Spectrometry (GC/MS). The confirmatory test uses a lower cut-off of 100 ng/mL for BZE. A specimen is only reported as positive if the BZE concentration is identified at or above this 100 ng/mL confirmation level. Therefore, in official testing contexts, any measured BZE concentration below 100 ng/mL is considered a low level that results in a negative test report.
Interpreting Trace Amounts Below the Standard
BZE levels below the 100 ng/mL confirmatory threshold are considered negative results by official testing standards, even if trace amounts are detected. Modern laboratory equipment can reliably detect concentrations as low as 5 ng/mL. Concentrations in the 5 ng/mL to 99 ng/mL range are too low to be confirmed positive under established guidelines.
These low levels usually indicate use that occurred further in the past, or very light use, where the BZE level has already dropped significantly during elimination. Trace amounts can sometimes be attributed to passive or environmental exposure, though cut-off levels are set high enough to account for this possibility.
Duration and Clearance
The elimination of BZE from the body is not a consistent process, which influences how long a low level remains detectable. Following use, BZE levels decline quickly, followed by a slower elimination phase that extends the detection window. The exact duration BZE remains in the system is dependent on individual factors like metabolic rate, body composition, and kidney function.
For an occasional user, BZE is typically detectable for two to four days after the last use before levels drop below the official cut-offs. However, for heavy or chronic users, the metabolite can accumulate, keeping BZE detectable for up to two weeks or longer, meaning a low reading may be the final stage of elimination following heavier use.