Table of Contents
Local anesthetic injections do NOT cause false positive test results for cocaine in urine tests! Urine testing for cocaine involves an immunoassay using antibodies against the major metabolites of cocaine. Ecgonine methyl ester and benzoylecgonine remain in the bloodstream for between 2 and 4 days after cocaine use . These chemicals are unique to the metabolism of cocaine and will not appear in the urine if the patient has been injected with lidocaine or other dental anesthetic.
In order to make the lab test kit, the manufacturer injects ecgonine methyl ester and/or benzoylecgonine into the veins of a large laboratory animal, such as a horse or a sheep. The animal’s immune system then naturally makes antibodies against them, and these antibodies circulate in the animal’s blood. The animal’s blood is then drawn, and the antibodies are extracted from the plasma. These antibodies are then refined and used in the testing kit to bind to the ecgonine metabolites in the testee’s urine. If the antibodies bind to their target metabolites, then the solution turns a specific color indicating a positive test. According to expert opinion, cross reactivity between urine immunoassay screens for these metabolites and substances other than cocaine are nearly nonexistent!
Legal testing issues
Even though mainstream opinion confirms the infallibility of the immunoassay for cocaine, the same cannot be said for other drugs. Immunoassays are not the best way to test for metabolites or the drugs themselves. They just happen to be the least expensive and most readily available type of urine test on the market. The natural function of antibodies is to recognize proteins characteristic of disease entities like viruses and bacteria. While antibodies are good at recognizing large protein molecules, they are not as specific in recognizing especially small molecules. Drug metabolites, as well as the drugs themselves have small molecular structures.
The argument against urine immunoassay testing is that the drug test kit manufacturer generally knows the rates of false positive results associated with any given batch of their test kits, but they are not often very forthcoming about this. The rate varies depending on the specificity of the batch of antibody that accompanies the kit. The fact that the manufacturer of the kits must acknowledge (eventually) that the tests are not infallible gives a good lawyer a legal loophole to slip through.
The ramifications of this are a bit complex. The only definitive way to confirm or refute a positive urine test for cocaine (or any other drug) is to perform a different and more expensive test called gas chromatography-mass spectrometry (GCMS). Furthermore, the test must be performed on the same sample. This test is irrefutable! A GCMS will either clear your name, or find you guilty in a court of law.
Unfortunately, these tests are expensive, and a prospective employer is under no obligation to retest your urine, since he can refuse to hire you for any reason except those based on sexual or racial discrimination.
On the other hand, if you already hold a job which you may lose due to a random drug test, or if there is a chance that the test might result in legal consequences beyond losing your job, then the employer or testing authority should run the more expensive GCMS test on the original sample to confirm your drug status. If the employer refuses, or if he did not retain the original sample in proper conditions and with a legal chain of custody, then you may have an actionable legal case against the employer.
Length of time drug abuse can be detected in urine
- Alcohol– 7-12 h
- Amphetamine– 48 h
- Methamphetamine–48 h
- Short-acting (e.g., pentobarbital)–24 h
- Long-acting (e.g., phenobarbital)–3 wk
- Short-acting (e.g., lorazepam)–3 d
- long-acting (e.g., diazepam)–30 d
- Cocaine metabolites–2-4 d
- Single use–3 d
- Moderate use (4 times/wk)–5-7 d
- daily use1–10-15 d
- Long-term heavy smoker–>30 d
- Codeine–48 h
- Heroin (morphine)–48 h
- Hydromorphone–2-4 d
- Methadone–3 d
- Morphine–48-72 h
- Oxycodone–2-4 d
- Propoxyphene–6-48 h
- Phencyclidine–8 d
List of substances that can cause false positive urine immunoassays
There are lots of other problems with drug testing, especially as it relates to employee screening in today’s large corporate structures. False positives may be the result of a range of problems from cross reaction with over-the-counter and prescription medications, to systemic conditions such as diabetes, or kidney and liver disease. Plain sloppiness on the part of the testing facility may also be a factor.
The following is a list of illegal drugs, each followed by a number of commonly used and legally available substances (many of them prescription drugs) that may cross-react and cause a false positive drug test.
Note that the use of prescription (DEA schedule II, III, IV or V) drugs without a doctor’s prescription is illegal and are grounds for the legal consequences stemming from a positive drug test. (Schedule I includes drugs such as heroine, LSD, ecstasy, designer and experimental drugs. None of these are legal to prescribe to the general public.)
Employers are private individuals under the law. They have a right to deny you employment for any reason (provided the reason is not based on racial or sexual discrimination). This means that an employer’s rights extend to demanding that a prospective employee agree not only to submit to a drug test before being hired, but also to signing an agreement that the employer may demand that the employee, once hired, must submit to drug tests on demand in the future.
For their part, employers have been forced by modern litigation practices to take a hard line against any employee who uses drugs. The mere presence of an employee who can be shown to be abusing illegal substances places that employer at huge risk of having to pay gigantic awards to a plaintiff and his lawyer. If you are unfairly targeted for termination of employment due to drug testing, you have become a victim of the perversions of American tort law.
Much is made of the citizens’ fourth amendment right to freedom from unreasonable search and seizure of person or property. Unfortunately, this right applies only to federal or state cases in which a search may result in legal sanctions such as prison time or fines paid to the state. Private parties such as an employee and an employer who have entered into a legal agreement requiring a search (the drug test) or a subsequent seizure (your job) based on the search are not covered by the fourth amendment.
While an employee drug test may result in the termination of the employee, and a prospective employee drug test (or refusal to submit to drug testing) may prevent a subject from being hired, these tests seldom result in state or federal charges being brought and therefore the subject’s legal rights in these matters is fairly limited.
What can you do if you feel that you were unfairly labeled a drug user due to a false positive drug test?
The majority of drug testing kits on the market are immunoassay tests (described at the top of this page). While false positive immunoassay tests are very rarely wrong, the cheaper kits have been known to produce false positives, as demonstrated in the table above. The only way to legally contest a false positive immunoassay test is to get a lawyer who is knowledgeable about this issue and then demand that a gas chromatography-mass spectrometrytest be used to confirm the presence of the actual drug metabolites in the original urine sample. A good lawyer should be able to argue for the re-testing of the urine, or, if the sample no longer exists argue that without advanced testing, the immunoassay results are inadmissible. This is NOT something that a letter from me, or any other authority can do. Only a good lawyer arguing in a court of law can accomplish this! Even if you beat the rap, your employer (and the judge) may require that you take random drug tests in the future, so even this method will probably not protect a person who habitually uses the drug.
Q. But I have a prescription for medical marijuana to treat chronic pain. I live in a state in which such prescriptions are legal. Can an employer legally fire me if I test positive for marijuana in my urine or blood?
A. YES, the employer can still fire you, even if you have a legal prescription for medical marijuana, or for any other drug that is illegal under federal law. Even if a state makes a drug legal under its own statutes, federal law trumps state law, and marijuana is still illegal according to federal statutes. On another level, an employer may choose to terminate any employee if the employer suspects that the employee might be impaired on the job.
Q. I live in Colorado where it is legal to buy and use marijuana for recreational purposes. can my employer still fire me?
A. Yes. The Colorado Supreme Court has ruled that businesses can fire employees who use marijuana during their off-time, including those with a legal prescription for medical pot.
Click here to be directed to a fairly good page explaining the ins and outs of drug testing.
Do NOT ask me to write notes to your employer regarding your innocence of illegal drug use due to false positive drug testing. I am not an expert in either drug law or the evolving ability of drug tests to winnow out false positive results. You will need to consult a lawyer who specializes in defending clients against wrongful termination