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         The JMJ Laboratories Limited toxicology newsletter
Issue No5

INTRODUCTION                therefore important to      structurally      similar
                            know what medication        drugs e.g. ephedrine
Cut off levels in           a person is on before       and its metabolites can
workplace drug testing      interpreting a positive     interfere    with    the
are      internationally    result.                     amphetamine assay as
recognised values for                                   ephedrine              is
groups of drugs to          SCREENING TEST              structurally similar and
determine whether a         LEVELS                      ‘cross reacts’ with the
sample is positive or       The purpose of the          amphetamine assay.
negative for that group     screening test is to
e.g          (SAMHSA        eliminate all negative
guidelines,        2001     samples quickly while       CONFIRMATION
(substance abuse and        highlighting samples        TEST LEVELS
mental health services      that require further        Gas chromatography
administration)). For       investigation (GC-MS).      Mass       spectrometry
screening this is for a     Screening test cut off      (GC-MS)       is      the
group of drugs e.g          levels are set at a point   reference method for
opiates,        whereas     where there is a            confirmation of drugs
confirmation is for a       demonstrably         high   of abuse samples. GC-
specific    drug      e.g   statistical probability     MS       looks        for
morphine. A positive        that the drug will be       individual drugs rather
result on screening or      detected if present.        than groups of drugs
confirmation does not       Results that fall below     and is therefore not
always mean that a          this are recorded as        subject to interference
drug is being abused as     negative even though a      from other drugs. GC-
some drugs screened         more sensitive method       MS is not used to
for are present in over     would      show       the   screen samples as it is a
the counter medication      presence of the drug        time consuming and
e.g         solphadeine     (Ellenhorn, 1997). As       expensive        method
contains        codeine     screening tests are for     whereas the screening
(opiate)             and    groups of drugs they        tests are relatively
diastalgesics    contain    can be subject to           quick.
propoxyphene.      It is    interference        from
                           if someone has a urine        results in a court of
As GC-MS looks for         concentration          for    law.         The main
individual drugs and
                           morphine of 1000ng/ml         accreditation required
screening tests look for
                           (positive) but drinks         of laboratories to prove
groups of drugs some
                           enough water to dilute        this      is      UKAS
samples can be positive
                           there sample 4 fold this      accreditation       (ISO
on      screening   and
                           would       reduce     the    17025).
negative              on
                           morphine concentration
confirmation      where
                           to 250ng/ml (negative).       REVISED CUT OFF
low amounts of several
                           To counter this the           LEVELS
drugs are present. An
                           creatinine                    Please see attached
example of this is as
                           concentration of all          table for cut off levels.
                           urine      samples       is
The screening cut off
                           determined and if this        REFERENCES
level for opiates is
                           falls               below
300ng/ml, so if a
                           1.77mmol/L (20mg/dl)          Ellenhorn, Ellenhorn’s
sample          contains
                           the       sample         is   medical toxicology 2nd
250ng/ml of morphine
                           considered dilute. If         edition (1997).
and codeine, this gives
                           the concentration falls       SAMHSA guidelines.
a combined level of
                           below        0.44mmol/L       Mandatory guidelines
500ng/ml and therefore
                           (5mg/dl) the sample is        for federal workplace
a positive screening
                           considered void and           drug testing. (1998).
result.              On
                           unsuitable for analysis       UK guidelines. United
confirmation by GC-
                           (UK guidelines 2001).         Kingdom        laboratory
MS the cut off is set at
                           If a drug is being            guidelines for legally
300ng/ml but as GC-
                           abused                 the    defensible workplace
MS looks for the
                           concentrations in the         drug testing (2003)
individual drugs rather
                           urine are often very
than a group of drugs
                           high so even if the
the sample is negative
                           sample is diluted a
for     morphine    and
                           positive result is still
codeine as both are
                           obtained e.g a 4 fold
present at 250ng/ml.
                           dilution        on        a
                           concentration           of
                           2000ng/ml of morphine
People will try and get    gives 500ng/ml which
round drugs of abuse       is still positive. Other
tests     by    various    adulteration       checks
methods the most           performed       on      all
common of these is by      samples           include
drinking large volumes     specific gravity and pH
of water as this dilutes   (UK guidelines, 2003)
the urine sample and
therefore            the   ACCREDITATION
concentration of any
                           All        laboratories
drugs present in it.
                           carrying    out   drug
This could change a
                           testing must be able to
result    from    being
                           legally defend their
positive to negative e.g
                                                                                                                              Appendix 1
                                                    ANALYTICAL CUT-OFF VALUES

 CANNABIS                                   50                   Delta - 9 - THC Acid                          15
 COCAINE                                   300                   Benzoylecognine                              150
 OPIATES                                                         Codeine                                      300
                                                                 Morphine                                     300
                                                                 6-MAM (Heroin)                                10
                                                                 Dihydrocodeine                               300
 METHADONE                                                       Methadone                                    250
                                                                 EDDP                                         250
 AMPHETAMINES                                                    Amphetamine                                  200
                                            300                  Methyl amphetamine                           200
                                                                 MDA, MDMA, MDEA                              200
 BENZODIAZEPINES                                                 Oxazepam                                     100
                                                                 7-Amino Nitrazepam                           100
                                                                 Temazepam                                    100
                                                                 Nordiazepam                                  100
 METHAQUALONE                               300                  Methaqualone                                 300
 PROPROXYPHENE                                                   Proproxyphene                                300
                                                                 Norpropoxyphene                              300
 BARBITURATES                               200                  Barbiturate Group                            150
 PHENCYCLIDINE                              25                   Phencyclidine                                 25
Cut-offs in accordance with UK Laboratory Guidelines for Legally Defensible Workplace Drug Testing

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