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Chain of custody is the movement and location of physical evidence from the time it is obtained until the time it is presented in court, and is used to prove the integrity of a piece of evidence. In order to track chain of custody, a paper trail is maintained so that personnel in possession of the evidence at different times can be identified easily and subpoenaed to testify during trial if needed.
For urine drugs of abuse testing in particular, it is important that the donor identify the specimen and that the urine cup is sealed in front of the donor, followed by the person who collected the specimen signing the chain of custody forms. (In the case of an unconscious patient in the emergency room, the nurse collecting the urine specimen can identify it in the patient’s place.) An example of what might happen next is as follows:
Police sergeant A seizes the urine sample collected from the defendant, and police officer B transports the specimen to a crime lab. At the crime lab, staff member C receives the urine specimen and scientist D analyzes it, detecting the presence of benzoylecgonine, the inactive metabolite of cocaine, using gas chromatography-mass spectrometry (GC/MS). Scientist D gives the result to senior scientist E of the crime lab, who confirms the result.
A, B, C, D, and E would all need to sign the chain of custody forms, and the prosecution would need to offer testimony by each person in the chain to identify and establish the condition of the evidence showing that the defendant abused cocaine.
A medical urine drug test is conducted when a patient suspected of overdosing is admitted to the emergency department, but this individual has not been involved in an accident or another situation in which he or she could be prosecuted if a drug test were to come back positive. Usually, urine drug screens conducted during medical drug testing are performed using immunoassays. Confirmation using a different analytical method such as GC/MS or liquid chromatography tandem-MS might not be conducted unless the ordering clinician requests it.
The result of a positive urine drug screen during medical drug testing is confidential information and cannot be used against the patient for any punitive action, such as reporting the result to his or her employer. Therefore, chain of custody is not needed during medical drug testing.
In contrast, confirmation of an initial positive immunoassay result is mandatory during legal drug testing because the result may be presented in court as evidence against the defendant. In these cases, chain of custody is essential.
Chain of custody is also used for newborn drugs of abuse screening, which falls under the category of legal drug testing. Usually, consent is obtained from the mother to conduct this testing. If the mother does not provide consent, however, the hospital legal team must be involved to see if a court order for drug testing of the newborn is necessary.
Although headspace GC is the standard method for legal alcohol testing, medical testing results for serum alcohol level are sometimes used as evidence to prosecute individuals charged with driving while impaired. However, chain of custody is not maintained in medical alcohol testing and it is up to the judge overseeing the case to decide whether such results can be admitted in a court of law.
In these cases, defense teams typically argue that medical alcohol testing results are not acceptable because there was no chain of custody. In such situations, a laboratory scientist should simply confirm that the specimen was not collected following chain of custody and let the prosecution pick up the battle.
Amitava Dasgupta, PhD, DABCC, is a professor of pathology and laboratory medicine at the University of Texas McGovern Medical School in Houston. E-Mail: Amitava.Dasgupta@uth.tmc.edu