Guide to Employment Screening

for Drug & Substance Abuse

Last modified: April 13, 2005

Copyright ^© [Regional Laboratory for Toxicology]. All rights reserved.

INTRODUCTION

This guide has been written for occupational physicians and nursing staff who need to deal with the issue of drug and substance abuse in the workplace. It is a description of some of the problems and pitfalls of drugs of abuse screening and the investigations currently available from the Regional Laboratory for Toxicology.

The use of illicit drugs for recreational purposes poses an increasing problem for British industry, both in terms of lost productivity from staff performing complex tasks possibly under the influence of agents affecting perception, and due to health and safety issues relating to the affected person and their colleagues. It is for these reasons that employment and pre-employment screening for drug abuse is performed.

Screening for drugs of abuse (as distinct from the investigation of volatile substance abuse) is carried out with urine specimens. A wide variety of prescription only and illicit drugs may be detected qualitatively by the screening procedures (Table 1).

It should be noted that analysis of urine specimens for "drugs of abuse" will only give information about current or quite recent drug usage. A specimen taken more than a few days after an episode of 'abuse' is likely to be negative on screening for most substances, with the notable exception of cannabis.

It is important to note that the range of substances detected in the screening procedure includes controlled drugs, prescription-only medicines, medicines available over-the-counter (OTC), and illicit drugs. It is always important to ensure that employees declare all prescribed and non-prescribed medication, including "herbal" preparations.

For medico-legal reasons, it may be necessary to follow chain-of-custody requirements, in the collection, labelling and transport of the specimens.

SPECIMEN COLLECTION

The appropriate specimen for screening for drugs of abuse is a 'spot' urine sample (~ 50 mL). It is important to ensure that the urine specimen provided by the client is valid and has not been substituted or adulterated in any way e.g. addition of water, bleach etc.

The specimen collected (use sterile plastic container without preservative) should be transferred into TWO 25 mL sterile plastic universal containers again without preservative. Each container should be given an identification number and bar-code and sealed with the tamper-proof seals provided, which should have been completed and signed as instructed. The two containers should then be sealed in the plastic bag and the request form completed fully prior to despatch to the Laboratory (see Table 1).

Each request must be authorised by a registered medical practitioner. If in doubt about a request - please contact the laboratory 0121 507 4135/6.

A urine specimen for drugs of abuse screening should be sent by courier or first class mail, but if there is likely to be a delay in dispatch, it should be kept in a 4 ^oC refrigerator prior to being recent to the laboratory.

LABORATORY TECHNIQUES AND QUALITY CONTROL

The laboratory uses a range of carefully controlled gas-chromatographic and immunoassay (Syva EMIT) techniques for screening for the presence of drugs of abuse in urine specimens. The laboratory aims to ensure a minimum of false 'negative' results, and that no false 'positive' results are reported. Confirmatory test are available for unexpected positive findings. The laboratory is also able to provide confirmation of findings using gas chromatography-mass spectrometry techniques. The Laboratory participates regularly in the U.K. National Quality Assurance Scheme (NEQAS) for drugs of abuse and has been to achieve a consistently high standard of performance. The "sensitivities" of the urine screening tests currently performed for employment purposes are shown in Table 2.

Only one of the duplicate specimen will be screened by the Laboratory. If a 'positive' result is obtained - the remaining duplicate sealed specimen is available for testing under supervision in another laboratory if required.

TESTS FOR THE DILUTION OF URINE

The Laboratory will determine the creatinine concentration of all urine specimens submitted for screening to detect "abnormally" dilute specimens i.e. those with a creatinine concentration below 1.8 mmol/L (0.2 g/L). Screening tests carried out on individuals who provide 'dilute' urine specimens (< 1.8 mmol/L) should be considered as being invalid and a repeat specimen obtained as soon as possible.

DETECTION OF OTHER SUBSTANCES

The screening procedure may also detect the presence of unsuspected drugs not included in Table 1 that might have some medical significance. It is the Laboratory's policy to report all significant findings to the company medical advisor.

HOW LONG AFTER USAGE CAN DRUGS BE DETECTED

There is no simple answer to this question, because it depends very much on the substance itself and on other factors such as dosage, frequency of abuse, and individual rates of drug metabolism and excretion; also on the sensitivity of the particular test carried out. As an approximate guide, drugs are likely to be detectable in urine within the time scales shown in Table 3.

POLICY ON REPORTING RESULTS

It is important to establish a correct policy for the reporting of laboratory results. All results will be reported to the factory medical officer or other suitable medical advisor. Results will NOT be reported to management or personnel departmental staff. The company should have an agreed in-house policy of dealing with 'positive' test results. The policy of the Laboratory is to discuss all positive findings directly with the company medical advisor.

LIMITS OF DETECTION

The limits of detection for drugs to be screened are shown in Table 2. These limits (where applicable) are those recommended by recognised agencies in the USA dealing with issues of employment screening.

BRIEF NOTES ON SOME INDIVIDUAL DRUGS AND DRUG GROUPS

ALCOHOL

Ethyl alcohol (ethanol) is measured by a gas chromatographic procedure which is able to differentiate it from other alcohols, notably methanol and isopropanol. The results of a urine ethanol assay will be expressed quantitatively relative to the limit of detection of 10 mg/dL. The quantitative measurement of ethanol in blood (which requires a 4 mL specimen in a fluoride-oxalate container) is the preferred test in chronic alcohol abuse or in an acutely intoxicated employee.

AMPHETAMINES

Abuse of amphetamines is relatively common in the West Midlands. The screening tests carried out in this Laboratory are able to distinguish amphetamine from many closely related compounds, some of which are also controlled drugs. Many OTC medicines contain substances e.g. ephedrine and phenylpropanolamine, that are structurally related to amphetamine; hence they can be identified in the "standard" screening procedure. Some other prescribed medicines that belong to the amphetamine class of drugs such as fenfluramine and phentermine can also be identified. In the case of methamphetamine abuse, its metabolite amphetamine may also be detected in urine. The screening tests can also detect a number of 'new' amphetamine-like drugs of abuse: such as methylenedioxyamphetamine (MDA) and methylenedioxymethamphetamine (MDMA, "ecstasy") and methylene dioxyethylamphetamine (MDEA). It should be noted that such screening tests are unable to differentiate between dextro (+) amphetamine (dexamphetamine) and equimolar racemic mixtures of dextro (+) and laevo (-) isomers that are present in "street" amphetamine. However, a new test is now available that is able to measure the ratio of (+) and (-) isomers of amphetamine.

BARBITURATES

Barbiturate abuse is now relatively uncommon. The screening procedure is able to detect the majority of common barbiturate drugs, but because of their low frequency of detection in drug abusers, barbiturates are not included as part of the 'routine' screening procedure, and they will only be screened for if specifically requested.

BENZODIAZEPINES

The abuse of benzodiazepines is relatively common, but the "standard" screening procedure is generally unable to distinguish between different benzodiazepines. Since a number of benzodiazepines share common pathways of metabolism it is not always possible to test for the abuse of specific benzodiazepines e.g. temazepam. or diazepam. A blood specimen may be required to resolve issues concerning the abuse of specific drugs within this class.

CANNABIS

The abuse of cannabis is extremely widespread, but the medical significance of its detection in urine can be uncertain. Because of its high fat-solubility, cannabis metabolites persist in the body and may be excreted in urine for many days or some weeks following usage.

COCAINE

The use of cocaine as its hydrochloride salt or the free base form (crack) is becoming increasingly common. The screening test carried out in this Laboratory is designed to detect the presence of the main cocaine metabolite, (benzoylecgonine) in urine. In heavy (binge) or chronic users, the presence of unchanged cocaine and the metabolite, ecgonine methyl ester (methylecgonine) will also be detected in urine by the chromatographic screening procedure.

LSD (Lysergic acid diethylamide)

There is some evidence for an increasing abuse of this hallucinogenic drug within the UK. "Dosages" of LSD are extremely small (< 100 µg) and subsequent concentrations in urine are very low (<1µ/L). An radioimmunoassay procedure for the detection of LSD in urine is available. However, confirmation of very low concentrations of LSD in urine can be very difficult. Measurement of LSD is not part of the routine screening procedure.

OPIATES

Abuse of heroin (diamorphine) is still widespread, although abuse of other opiates such as codeine and dihydrocodeine (DF118) is also common. The "standard" screening procedure is able to differentiate between the recent usage the three major opiates - heroin, codeine and dihydrocodeine. Following heroin usage, only morphine is commonly detected in urine; 6-monoacetyl morphine (MAM) may also be detected following relatively recent heroin usage. Following codeine usage, a small amount of morphine as a minor metabolite is commonly observed. Therefore it may be difficult to distinguish between the abuse of heroin-plus-codeine, and the abuse of codeine alone, when 1 or 2 days have elapsed from the time of the ingestion. Following dihydrocodeine usage only dihydrocodeine and small quantities of dihydromorphine will be detected. Dihydrocodeine is not converted to morphine. Pholcodine, an opiate antitussive agent in several OTC medicines, is detected by the immunoassay screening procedure, but it is not converted to morphine or codeine and does not interfere with the confirmatory tests carried out to differentiate between the opiates which may be present in urine. Recent ingestion of poppy seeds in the diet may cause problems of interpretation, where large quantities have been taken.

Additional confirmation techniques involving gas chromatography-mass spectrometry can be applied to the confirmation of findings in difficult cases.

DETECTION OF OPIATE ABUSE

* May only be detected following recent heroin use.

PHENCYCLIDINE ("Angel Dust", PCP)

Currently, there is no evidence for any significant availability or abuse of this drug in the UK. It is possible to detect the presence of this drug in urine, using a specific radioimmunoassay procedure. It is however not part of the routine screening procedure.

VOLATILE-SUBSTANCE-ABUSE

The Laboratory is able to offer a service for the detection of volatile-substance-abuse (aerosol, glue or solvent inhalation). However, the range of substances involved is very wide, and their detection with good sensitivity and specificity can sometimes be difficult, particularly if more than 12-24 hrs has elapsed since abuse. A 10 mL whole blood sample - heparinised or EDTA - is required for this investigation; great care must be taken to avoid gel separators and contamination with exogenous volatile substances. Please contact the laboratory directly before sending such specimens.

CONTACT POINTS

Dr. S George, Senior Biochemist, Section Head, 'phone (0121) 507 6029

Dr R A Braithwaite, Head of Department, 'phone (0121) 507 4134

FAX number of Laboratory office: (0121) 507 6021

Table 1. DRUGS SCREENED FOR IN THE ROUTINE URINE DRUG ABUSE SCREENING REQUEST

1. Standard Immunoassay Screen (All specimens)

Amphetamines *

Benzodiazepines

Cocaine (metabolite)

Cannabinoid (50 µg cut-off)

Methadone

Opiates *

Urine Creatinine

* Additional confirmation tests performed on all "positive" tests at no extra charge.

2. Additional Substances Screened for by Specific Request

Alcohol

Barbiturates

Chlormethiazole

Cyclizine

Dextropropoxyphene

Diethylpropion

Dipipanone

Ecstasy (MDMA) and related drugs (MDA, MDEA)

Ketamine

LSD

Methadone metabolite (EDDP)

Pethidine

Phencyclidine (PCP)

Phentermine

3. Additional Substances Screened for by Specific Request for which an additional charge will be levied.

Buprenorphine

Resolution of d- and l- isomers of amphetamine

Table 2. SENSITIVITIES OF URINE SCREENING AND CONFIRMATION TESTS FOR DRUGS OF ABUSE

At concentrations below the limit of detection, the drug (or metabolite) will not normally be detected by the usual screening procedure. A result reported as 'positive' in a screening test implies that the concentration of drug present is in excess of the limit given here. Note that the sensitivity of drug detection will be reduced in dilute urine specimens.

NA = Not applicable.

The limits of detection cited above are the same as those used by most other UK laboratories performing drugs of abuse screening, and conform to the Substance Abuse and Mental Health Services Administration (SAMHSA) formerly the National Institute on Drug Abuse (NIDA) whose guidelines which are mandatory for drug screening laboratories in the US.

Table 3. APPROXIMATE DETECTION TIMES OF SOME COMMON DRUGS IN URINE*

* Note that detection times are only very approximate and are very dependent upon the dose, its frequency, route of administration and urine excretion/dilution.

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