Drug Screening: Actual Status, Pitfalls and Suggestions for Improvement Drogenscreening: Gegenwa¨ Rtiger Stand, Fehlermo¨ Glichkeiten Und Verbesserungsvorschla¨Ge
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J Lab Med 2004;28(4):317–325 ᮊ 2004 by Walter de Gruyter • Berlin • New York 2004/03304 Drug Monitoring und Toxikologie Redaktion: V. W. Armstrong Drug screening: Actual status, pitfalls and suggestions for improvement Drogenscreening: Gegenwa¨ rtiger Stand, Fehlermo¨ glichkeiten und Verbesserungsvorschla¨ge Wolf R. Ku¨ lpmann* pretierbar. In Wirklichkeit mu¨ ssen viele Aspekte beru¨ ck- sichtigt werden, um einen aussagekra¨ ftigen Befund zu Klinische Chemie, Medizinische Hochschule Hannover, erhalten, z.B. Pra¨ analytik, Spezifita¨ t und Empfindlichkeit Hannover, Germany des Verfahrens oder Qualita¨ tssicherung. Obwohl die Abstract mechanisierten Meßverfahren naturgema¨ ß quantitative Ergebnisse liefern, wird aufgezeigt, daß es sich in der Immunoassays for drug screening are often regarded as Regel empfiehlt, qualitative Befunde zu erstellen. Die procedures which are easily performed and interpreted. Verfahren erlauben aber im Gegensatz zu den auch fu¨r But in fact, many aspects have to be considered to diese Zwecke verwendeten Teststreifen die Entschei- obtain a meaningful result. Among these are sampling, dungsgrenze (cut-off) der jeweiligen Fragestellung anzu- specificity and sensitivity of assays, and quality assess- passen, z.B. bei akuter Intoxikation, chronischem Abusus ment. Although the mechanised procedures yield quan- oder U¨ berwachung des Drogenentzugs. titative results, there are good reasons to generally report Ein schwerwiegender Nachteil von Immunoassays zum qualitative findings. The mechanised procedures allow Nachweis von Amphetamin und a¨ hnlichen Substanzen, the adjustment of the cut-off concentration to the clinical Barbituraten, Benzodiazepinen und Opiaten besteht dar- setting, e.g. in the case of acute intoxication, chronic in, daß eine starke Kreuzreaktivita¨ t des Antiko¨ rpers abuse or drug withdrawal, an important advantage as gegenu¨ ber pharmakologisch wenig wirksamen Verbin- compared to test strips. Procedures for the detection of dungen bestehen kann, wa¨ hrend stark wirksame Sub- amphetamines, barbiturates, benzodiazepines or opiates stanzen der Gruppe, die in entsprechend niedriger are hampered by the fact that the analytical signal is in Konzentration vorliegen, wegen geringer Kreuzreaktivita¨t principle not related to the pharmacological effect of the ein vergleichsweise kleines analytisches Signal erzeugen contributing drug. A proposal for adjusting the analytical und so dem Nachweis entgehen ko¨ nnen. Es wird eine response to the pharmacodynamic action of a com- Empfehlung vorgelegt, wie empfindlich Pharmaka dieser pound is presented, as well as a list of drugs for which Gruppen unter Beru¨ cksichtigung ihrer Pharmakodynamik immunoassays are required. This may give guidance to nachweisbar sein sollten. Die entsprechende Aufstellung manufacturers for improving and developing assays. Pro- soll den Herstellern von Immunoassays Hinweise zur Ver- cedures for individual compounds should in general spe- besserung ihrer Verfahren geben. Weiter werden Sub- cifically detect the pertinent metabolite in urine as a proof stanzen aufgefu¨ hrt, fu¨ r die noch einfach durchfu¨ hrbare of drug uptake. Hydrolysis is mandatory in case of poor Nachweismo¨ glichkeiten beno¨ tigt werden. Nachweisver- cross-reactivity of the antibody with the excreted fahren fu¨ r einzelne Substanzen sollten in der Regel zum conjugates. Nachweis der Ko¨ rperpassage spezifisch nur den ent- sprechenden Metaboliten im Urin erfassen. Keywords: adulterants; confirmation analysis; immuno- Bei ungenu¨ gender Kreuzreaktivita¨ t der Antiko¨ rper assay; quality assessment; sensitivity; specificity; test gegenu¨ ber den u¨ berwiegend ausgeschiedenen Konju- strips; trend control. gaten muß dem Meßverfahren ein Hydrolyseschritt vorausgehen. Zusammenfassung Immunoassays zum Drogenscreening gelten vielfach als Schlu¨ sselwo¨ rter: Besta¨ tigungsanalyse; Empfindlichkeit; leicht durchfu¨ hrbar und ihre Ergebnisse als leicht inter- Immunoassay; Qualita¨ tssicherung; Spezifizita¨ t; Teststrei- fen; Verfa¨ lschungsstoffe; Verlaufskontrolle. *Correspondence: Prof. Dr. med. Wolf Ru¨ diger Ku¨ lpmann, Klinische Chemie, Medizinische Hochschule Hannover, Carl- Neuberg-Str. 1, 30625 Hannover, Germany Tel.: q49 511 532 6613 In this paper, drug screening is mainly confined to ana- Fax: q49 511 532 8614 lytical procedures used for the detection of drugs in urine 318 W.R. Ku¨ lpmann: Drug screening Table 1 Characteristics of freshly voided urine. Temperature: 32.0–37.78C temperature below 308C indicates an illegitimate sample Osmolality: 400–800 mmol/kg lower osmolality indicates a diluted sample Mass density: 1.003–1.030 kg/l lower mass density indicates a diluted sample Creatinine concentration: G9 mmol/l lower concentration indicates diluted urine, below 2.7 mmol/l dilution is obvious Nitrite: -125 mg/l a concentration exceeding 500 mg/l indicates contamination with adulterants Chromate: trace a concentration exceeding 100 mg/l indicates contamination with adulterants pH: 4–8 lower or higher values indicate contamination with acidic or alkaline solutions or substances by immunoassays. Immunoassays are commercially sample w2x. The solution contains another substance available for the following drugs in urine: which is not excreted in the urine to detect direct spoiling Amphetamines of urine with the test solution. Barbiturates It should be taken into account that addicts rather Benzodiazepines often suffer from hepatitis B or C as well as HIV, and Cannabinoids (THC) samples, especially blood or serum, should be handled Cocaine / Cocaine metabolite (Benzoylecgonin) cautiously to avoid infection. Lysergic acid diethylamide (LSD) Methadone / Methadone metabolite (EDDP) Methaqualone Opiates (total) and 6-Acetylmorphine Quality assessment Phencyclidine Propoxyphene Immunoassays, which are run on mechanised analysers, Tricyclic antidepressants yield by their very nature quantitative results (although a The reagents are certified for the use in urine. For the qualitative finding will be reported). Therefore, internal use in serum, dedicated reagent kits are available for tri- quality control should be performed according to the cyclic antidepressants, barbiturates and benzodiaze- guidelines in the same way w3x as for other measurable pines. The use of reagents for materials other than those quantities expressed on a ratio scale. The coefficient of declared is excluded from the manufacturer’s warranty variation (CV) for imprecision between series as an esti- and is at one’s own risk w1x. The risk may be low with mate of reproducibility should be below 7% for a sub- some assays of a certain manufacturer and high with his stance concentration near the cut-off concentration. In other assays or assays of other manufacturers. It can be practice, however, CVs up to 11% are observed. Official reduced if e.g. the serum is extracted and the dried criteria which need to be met have not been established extract is reconstituted with drug free urine. in Germany yet. Single measurements should not deviate Spot urine is appropriate for drug screening, but in from the mean more than 3-fold compared to the previ- some settings (examination of drug addicts, workplace, ously calculated CV. Knowledge of the precision at the car drivers, military personnel), adulteration has to be cut-off concentration is most important for the medical expected and a chain of custody must be set up. evaluation of the measurement results. Precision at high Through the internet, testees can obtain detailed advice concentrations may be poor because of a low steepness on how to ‘‘fool the bladder cops’’ and ‘‘how to beat drug of the calibration curve in this range. If control urine is tests’’. If adulteration is suspected, the laboratory should used containing the same drug as the calibrator of the investigate the freshly voided urine (Table 1). Dilution of assay, the mean should not deviate by more than 10% urine may be achieved by e.g. adding tap water or from the certified value (estimation of trueness). Appro- through excessive drinking. Readjustment of creatinine priate control material is available from the manufacturers to disguise dilution is tried by addition of creatine, which of the pertinent reagents or from companies specialised is easily available to body builders. Creatine at high con- in control materials w4x. centration is falsely taken for creatinine by enzymatic Test strips used for drug screening yield by their very procedures, but not by the Jaffe reaction. A general indi- nature qualitative results. Therefore, quality assessment cation for the presence of adulterants that interfere with is hampered and cannot be performed in the same the relevant method may be obtained by a sample check meticulous way as in quantitative measurements w5x.At assay (Microgenics, Passau). Dedicated procedures are best, control urine with the pertinent drug at a concen- commercially available for particular, often used adulter- tration exceeding the cut-off concentration is regularly ants. Recently, it was proposed that patients should be used to check whether the strips (still) yield valid findings. asked to drink a solution containing a marker substance, However, there is always some doubt whether the eval- which is excreted in the urine to detect an illegitimate uated strip is representative for those remaining. After a W.R. Ku¨ lpmann: Drug screening 319 while, the check has to be repeated to exclude deterior- noassays of different manufacturers may indeed have ation during storage. different