Tetrahydrocannabinol (THC) is the primary psychoactive compound found in cannabis. When a child tests positive for marijuana exposure, the test detects an inactive compound in their system, not active THC. This substance is the main breakdown product, 11-nor-9-carboxy-Δ9-tetrahydrocannabinol (THC-COOH). The presence of this metabolite confirms the child has been exposed to and metabolized THC, highlighting a situation of medical and social concern.
Direct Exposure Through Accidental Ingestion
Accidental ingestion is a dangerous route of exposure, often leading to severe toxicity in young children. Cannabis products are increasingly available in edible forms, such as gummies, cookies, and chocolate bars, which look identical to conventional snacks. These products present a high risk because they are appealing to children and lack the distinct odor or appearance of cannabis flower.
The danger is amplified by the high concentration of THC in many modern edibles, where a single item can contain multiple adult doses. When a small child consumes an entire edible, the resulting dose relative to their body weight can be significantly toxic. Ingested THC effects are delayed compared to inhalation, taking two to four hours to manifest, meaning a large amount may be consumed before symptoms appear.
Symptoms range from excessive sleepiness, poor coordination, and vomiting to severe effects like respiratory depression, seizures, and unresponsiveness. Highly concentrated cannabis oils, tinctures, and topical products also pose a direct exposure risk. These non-edible forms can be accidentally ingested or absorbed through the skin.
Exposure Pathways Via Inhalation and Biological Transfer
Indirect exposure to THC can occur through environmental or biological transfer, leading to a positive test result without direct consumption. Inhalation of secondhand cannabis smoke or vapor is a documented pathway for detectable levels of the metabolite THC-COOH in a child’s urine. This exposure includes aerosolized particles from vaping devices.
Studies have demonstrated that children living in households where cannabis is smoked have a higher likelihood of testing positive for the metabolite. While environmental contamination is generally less potent than ingestion, the detection of THC-COOH confirms systemic absorption.
Biological transfer occurs when THC passes from a pregnant or breastfeeding parent to the child. THC is highly fat-soluble, allowing it to easily cross the placental barrier and expose the developing fetus in utero. Following birth, the compound concentrates in breast milk, where it can be detected for an extended period after maternal use. This prolonged presence results in the infant absorbing the compound and metabolizing it into THC-COOH.
How Drug Screening Identifies THC in Children
A positive THC test result hinges on detecting the inactive metabolite, THC-COOH, rather than the psychoactive parent compound, delta-9-THC. THC is broken down by the liver into THC-COOH, which is the most persistent metabolite. Since THC-COOH is not psychoactive, its presence confirms prior exposure and metabolism.
The standard procedure for pediatric drug screening often begins with an immunoassay, a rapid test that screens for cannabinoids, typically in urine. Presumptive positive results must then be confirmed using a highly precise technique. Confirmatory testing, such as gas chromatography-mass spectrometry (GC-MS) or liquid chromatography-mass spectrometry (LC-MS), identifies the specific structure of the THC-COOH molecule.
Laboratories use established cut-off levels to determine if a result is reported as positive. For THC-COOH in urine, a common screening cut-off is 50 nanograms per milliliter (ng/mL), with a confirmatory cut-off often set at 15 ng/mL. In pediatric or child protection contexts, a lower limit of quantification may be used to detect trace exposure relevant for clinical or legal interpretation.
Beyond urine, other biological samples are used depending on the suspected timing of the exposure. Hair samples incorporate drug metabolites as the hair grows, providing a record of exposure over several months. For newborns, meconium testing analyzes the infant’s first stool to establish evidence of in utero exposure during the second and third trimesters of pregnancy.
Immediate Steps Following a Positive Test Result
The immediate step following a child’s positive THC test result is to seek medical evaluation. If the child displays symptoms of toxicity, such as extreme drowsiness or difficulty breathing, caregivers should call emergency services or the Poison Control Center immediately. Medical personnel provide supportive care, monitoring the child’s breathing and heart function until the effects of the THC wear off.
Accidental ingestion requires prompt medical attention, as concentrated doses in edibles can lead to severe and prolonged symptoms requiring hospitalization. A confirmed positive test result for a substance in a child can also trigger mandated reporting procedures. Healthcare providers may be legally required to report the findings to local child protective services, depending on the jurisdiction and the context of the positive test.