A Difficult Challenge for the Clinical Laboratory: Accessing and Interpreting Manufacturer Cross-Reactivity Data for Immunoassays Used in Urine Drug Testing

Evaluation of Immunoassay Performance for the Detection of Opioids in Urine

BACKGROUND

Immunoassay drug screens provide rapid analysis of urine for the presence of therapeutics and drugs of abuse. Compared to definitive (confirmatory) methods, immunoassays are prone to false-positive and -negative results. Laboratories generally rely on manufacturers' claims regarding method sensitivity and specificity; few have the resources to independently verify performance. In this study, we review the performance of our opioid immunoassay drug screens in comparison to a definitive method.

METHODS

Results of 859 urine samples tested via opioid immunoassay screens for buprenorphine, fentanyl, methadone metabolite (2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine; EDDP), opiates, and oxycodone were compared to definitive results obtained via liquid chromatography-tandem mass spectrometry (LC-MS/MS). The data examined here included multiple samples from individual patients. Our quantitative LC-MS/MS method includes 19 opioid compounds (parent drugs plus metabolites).

RESULTS

Immunoassay sensitivity and specificity ranged from 96% to 100% and 84% to 99%, respectively. The sensitivity and specificity of these screens were similar to manufacturers' claims with some exceptions. The opiates immunoassay had poor performance when limiting the comparison to its target compound, morphine, but improved when including all compounds listed in the manufacturer's instructions for use (IFU). While demonstrating good sensitivity, the buprenorphine immunoassay demonstrated lower specificity than stated in the IFU.

CONCLUSIONS

The opioid immunoassay screens in use at our facility compared favorably to a definitive LC-MS/MS method. The urine fentanyl screen had the lowest sensitivity (96%) and had a specificity of 97%. The urine buprenorphine assay was the least specific (84%) and had a sensitivity of 99%.

Laboratorian Interpretation of Drug Testing Results in Pain Management: Lessons From College of American Pathologists Proficiency Testing

CONTEXT.—

Accurate interpretation of drug test results is key to appropriate patient care in numerous settings, including pain management. Despite recommendations that providers should consult laboratory professionals for guidance when necessary, literature demonstrating laboratorian expertise in drug test interpretation is lacking.

OBJECTIVE.—

To evaluate participating laboratories' performance on the case-based, interpretive ("dry") challenge included with each Drug Monitoring for Pain Management proficiency testing program from 2012-2023.

DESIGN.—

All challenges (n = 23) required participants to identify if drug test results were consistent or inconsistent with prescribed medications in the case history. Relevant medications, presumptive and confirmatory drug test results, and participant responses were extracted from program summary reports and examined for performance and common themes.

RESULTS.—

Overall, 91.8% (6821 of 7431) of participant responses correctly identified whether drug testing was consistent with medications. There were 8 challenges with participant scores less than 91.8% (range, 59.8% [49 of 82 responses] to 88.9% [193 of 217 responses]). Common knowledge gaps identified in these challenges included false-positive presumptive (screening) results, minor metabolism of opiates, and recognizing that presence of a nonprescribed drug is inconsistent with prescribed medications. Although some participants repeatedly responded incorrectly, there were no associations between laboratory type, personnel responding, or analytical performance and incorrect responses to interpretative challenges.

CONCLUSIONS.—

Program participants performed well overall, but several concerning educational gaps were identified. Laboratorians have a role in providing interpretative guidance for drug testing and should emphasize ongoing education to ensure competence in the setting of constantly changing prescribed and nonprescribed drug use.

[Urine Screening for Narcotics under Court-Imposed Abstinence Requirements: Comparative Validity of Forensic-Toxicological Analyses with Involvement of Public Health Services]

AIM OF THE STUDY

Assessment of the comparative validity between qualitative and quantitative analyses of urine screenings for defined narcotics residues under court-imposed abstinence restrictions.

METHODS

Following the introduction of a valid marker system which, based on the application of a defined sugar substance and its detection in the urine of person under probation in 2006, urine samples were assayed in administrative cooperation by a Bavarian public health office for probationary services for evidence of narcotics. The urine samples were sent to an external laboratory in order to carry out forensic toxicological analyses for defined narcotics. The qualitative and quantitative laboratory results were reported back to the public health department so that a digital-based data set of a total of 380 persons with more than 27,000 individual analyses from a total of 14 consecutive calendar years could be established and retrospectively evaluated in an anonymised form.

RESULTS

The overall prevalences of findings positive for narcotics were 2.7% (n=366 of 13,531) for the qualitative and 2.6% (n=348 of 13,525) for the subsequent quantitative result categorisations, with cannabis and opiates being detected most frequently in both test methods. Using the kappa coefficient as a quantitative measure for the comparative validity of both test methods, the test results showed the highest agreement (1.000) for buprenorphine and lowest agreement for PCP (0.880). No age- and gender-specific stratifications could be recorded for a total of ten different narcotic substances; substance-specific case numbers differed among the analyses.

CONCLUSION

Based on the strong to very strong correspondences between qualitative and quantitative narcotics analysis results, it could be assumed that both analysis methods accurately recorded violations of abstinence requirements and were to be classified as sufficiently substantiating for judicial decisions under the Narcotics Act (Betäubungsmittelgesetz, BtMG). According to these results, the content of urine screenings for narcotics controlling abstinence should be discussed.

Effectiveness of a Reliable Toxicological Analysis for a Correct Diagnosis of Acute Intoxication in Pediatrics: 2-Year Experience of an Analytical Toxicological Laboratory

OBJECTIVES

This study aimed to assess the role of the laboratory of toxicology as a support for a correct diagnosis of intoxication through the application of a reliable analytical approach, critically designed to meet pediatric needs.

METHODS

Data collected from 360 cases of suspected intoxications in pediatric patients (aged 1 day to 17 years) during the period 2018 to 2019 are presented. Toxicological analyses were performed through different techniques (immunoassay and chromatography) with parameters (limit of detection and cut-off) adjusted according to pediatric needs to produce reliable toxicological data for a wide number of prescription drugs, drugs of abuse, and poisons.

RESULTS

We present results about (1) agents involved in suspected poisonings and the methods adopted for a definite analytical diagnosis, (2) the assessment of the concordance of results for analyses proceeded by different techniques, and (3) the percentage of agreement between analytical result and clinical suspicion.

CONCLUSIONS

An analytical approach critically designed to minimize misinterpretation of laboratory data and able to provide reliable results for a wide number of substances in a time compatible with the urgency represents a useful support for a correct diagnosis of intoxication in pediatrics.

Can Umbilical Cord and Meconium Results Be Directly Compared? Analytical Approach Matters

Maternal drug use during pregnancy is a significant concern. Drug-exposed newborns are often born premature and may suffer from birth defects, neonatal abstinence syndrome and cognitive and developmental delays. Because of this, testing of neonatal specimens is carried out to assess fetal drug exposure during pregnancy. Umbilical cord tissue (UC) and meconium are commonly used specimens for this purpose. However, comprehensive studies comparing drug positivity rates and concentration in the two specimen types are lacking. To this end, 4,036 paired UC and meconium specimens originating from 13 states within the USA were identified, and retrospective analysis of drug positivity rates and drug concentration was performed for 31 analytes in 5 drug classes. Testing for 11-Nor-9-carboxy-tetrahydrocannabinol (THC-COOH) is a separate orderable for UC specimen at our laboratory, so a second data set was created for evaluation of this drug analyte with 2,112 paired UC and meconium specimens originating from 11 states. Testing of UC was performed by semi-quantitative liquid chromatography-tandem mass spectrometry (LC-MS-MS) assays, whereas, for meconium, an immunoassay-based screening preceded LC-MS-MS confirmation tests. Results generated for UC and meconium specimens were therefore compared for a total of 32 drug analytes from 6 drug classes. Drug concentrations for analytes were higher in meconium compared to UC, with the exception of phencyclidine. Despite this, the positivity rates for individual analytes were higher in UC, with the exception of THC-COOH and cocaine. Furthermore, analysis for multidrug positivity revealed that THC-COOH and opioids were the most common multidrug combination detected in both matrices. In conclusion, this study suggests that for most drug compounds, UC was more analytically sensitive to assess neonatal drug exposure by current methodologies. Additionally, by demonstrating that meconium has higher drug concentrations for most compounds, this study sets the stage for developing more sensitive assays in meconium.

The analytical performance of six urine drug screens on cobas 6000 and ARCHITECT i2000 compared to LC-MS/MS gold standard

BACKGROUND

Immunoassays provide a rapid tool for the screening of drugs-of-abuse (DOA). However, results are presumptive and confirmatory testing is warranted. To reduce associated cost and delay, laboratories should employ assays with high positive and negative predictive values (PPVs and NPVs). Here, we compared the results of urine drug screens on cobas 6000 (cobas) and ARCHITECTi2000 (ARCHITECT) platforms for six drugs against LC-MS/MS to assess the analytical performance of these assays.

METHODS

Eighty nine residual urine specimens, which tested positive for amphetamine, THC-COOH, benzoylecgonine, EDDP, opiates and/or oxycodone during routine drug testing, were stored frozen until later confirmation by LC-MS/MS. Immunoassays were performed on cobas and ARCHITECT using a split sample. A third aliquot from these samples was tested by LC-MS/MS to assess the percentage of false positive, false negative, true positive and true negative results and calculate the PPVs and NPVs for each immunoassay.

RESULTS

The PPVs of THC-COOH and EDDP assays were 100% on both platforms. Suboptimal PPVs were achieved for oxycodone (cobas, 57.1% vs ARCHITECT, 66.7%), amphetamine (77.8 vs. 100%), opiates (80.0 vs. 84.6%) and benzoylecgonine (88.9 vs. 84.2%) assays. The NPV was 100% for cobas and ARCHITECT oxycodone assays. Lower NPVs were achieved for THC-COOH (cobas, 28.6% vs ARCHITECT, 25.0%), EDDP (72.7% for both assays), benzoylecgonine (74.4% vs 73.8%), amphetamine (83.3% vs 82.8%) and opiates (100% vs 85.3%).

CONCLUSION

Overall, cobas and ARCHITECT urine drug screens have comparable analytical performance. Confirmatory testing is warranted for positive test results especially for oxycodone, amphetamine, opiates and cocaine. Negative drug screen results must be interpreted with caution especially for THC-COOH, EDDP, benzoylecgonine, amphetamine and opiates.

Tetracaine from urethral ointment causes false positive amphetamine results by immunoassay

BACKGROUND

Amphetamine urine drug screening by immunoassay is prone to cross-react with other compounds leading to false positive results. Tetracaine is a local anesthetic drug used in the clinical setting as an ointment during urinary catheterization. In our laboratory, tetracaine is often detected by gas chromatography-mass spectrometry in the urine of patients admitted in the emergency department with false positive amphetamine results. The objectives of this study were to investigate if there was cross-reactivity to tetracaine in an amphetamine immunoassay and to retrospectively evaluate the potential contribution of tetracaine to false positive amphetamine results.

METHODS

An interference study was conducted using negative urine samples spiked with increasing concentrations of tetracaine hydrochloride and analyzed with the CEDIA Amphetamine/Ecstasy immunoassay. Retrospectively, urine samples of patients which yielded positive amphetamine immunoassay results and were analyzed by gas chromatography-mass spectrometry were reviewed (n = 417). The presence of tetracaine and/or other drugs by gas chromatography-mass spectrometry were gathered.

RESULTS

Tetracaine caused false positive amphetamine results by immunoassay (cut-off 1000 µg/L) with a concentration of above 40 mg/L. Retrospective analysis of all positive amphetamine immunoassay samples showed that in 45 out of the 417 (10.8%) urine samples no amphetamine-like derivative was identified by gas chromatography - mass spectrometry. In 37 out of 45 (82.2%) of these false positive cases tetracaine was detected, of whom 59.5% (22/37) had an estimated tetracaine concentration of ≥40 mg/L.

CONCLUSIONS

This study confirmed the interference of tetracaine in the CEDIA Amphetamine/Ecstasy immunoassay and that tetracaine may have contributed to around 80% of the false positive amphetamine cases in the urine samples of patients admitted to the emergency department at our institution.

Interpretation and Utility of Drug of Abuse Screening Immunoassays: Insights From Laboratory Drug Testing Proficiency Surveys

Context.—

Urine drug testing is frequently ordered by health care providers. Immunoassays are widely used for drug testing, yet have potential limitations, including variable cross-reactivity. The last decade has seen worsening of a prescription drug abuse epidemic.

Objective.—

To use data from a College of American Pathologists proficiency testing survey, Urine Drug Testing, Screening, to determine and summarize the characteristics, performance, and limitations of immunoassays.

Design.—

Seven years of proficiency surveys were reviewed (2011–2017).

Results.—

Rapid growth was seen in participant volumes for specific immunoassays for synthetic opioids (eg, buprenorphine, fentanyl, oxycodone) and 3,4-methylenedioxymethamphetamine (“ecstasy”). Participant volumes remained high for immunoassays targeting less commonly abused drugs such as barbiturates and phencyclidine. For opiate immunoassays, the number of laboratories using a 2000 ng/mL positive cutoff remained stable, and an increasing number adopted a 100 ng/mL cutoff. Opiate and amphetamine immunoassays showed high variability in cross-reactivity for drugs other than the assay calibrator. Assays targeting a single drug or metabolite generally performed well on drug challenges.

Conclusions.—

Survey results indicate strong clinical interest in urine drug testing and some adoption of new assays. However, urine drug testing availability does not parallel prevailing patterns of drug prescribing and abuse patterns. In particular, specific immunoassays for synthetic opioids and a lower positive cutoff for opiate immunoassays may be underused, whereas immunoassays for barbiturates, methadone, propoxyphene, and phencyclidine may be overused. Laboratories are encouraged to review their test menu, cutoffs, and assay performance and adjust their test offerings based on clinical needs and technical capabilities.

Accidental intoxications in toddlers: lack of cross-reactivity of vilazodone and its urinary metabolite M17 with drug of abuse screening immunoassays

Background

Vilazodone is an FDA approved medication used to treat major depressive disorder. The authors describe two cases of accidental vilazodone exposure in toddlers who presented with symptoms similar to amphetamine exposure and also with unexplained positive amphetamine urine immunoassay drug screens. Given a lack of published data on cross-reactivity of vilazodone and its metabolites with drug of abuse screening tests, the authors investigated drug of abuse immunoassay cross-reactivity of vilazodone and metabolites using computational and empirical approaches.

Methods

To ascertain the likelihood that vilazodone would cross-react with drug of abuse screening immunoassays, the authors assessed the two-dimensional (2D) similarity of the vilazodone parent molecule and known metabolites to an array of antigenic targets for urine immunoassay drug screens. To facilitate studies of the commercially unavailable M17 metabolite, it was prepared synthetically through a novel scheme. Urine and serum were spiked with vilazodone and M17 into urine (200–100,000 ng/mL) and serum (20–2000 ng/mL) samples and tested for cross-reactivity.

Results

Computational analysis using 2D similarity showed that vilazodone and metabolites have generally low similarity to antigenic targets of common drug of abuse screening immunoassays, predicting weak or no cross-reactivity. The M17 metabolite had 2D similarity to amphetamines and tricyclic antidepressants in a range similar to some other compounds exhibiting weak cross-reactivity on these immunoassays. Cross-reactivity testing was therefore performed on two different urine amphetamines immunoassays and a serum tricyclic antidepressant immunoassay. However, actual testing of cross reactivity for vilazodone and the M17 metabolite did not detect cross-reactivity for any urine amphetamines screen at concentrations up to 100,000 ng/mL and for a serum tricyclic antidepressants assays at concentrations up to 2000 ng/mL.

Conclusion

While the vilazodone metabolite M17 has weak 2D structural similarity to amphetamines and tricyclic antidepressants, the current study did not demonstrate any experimental cross-reactivity with two different urine amphetamines immunoassays and a serum tricyclic antidepressant immunoassay. Vilazodone ingestions in young children present a diagnostic challenge in their similarity to amphetamine ingestions and the lack of routine laboratory tests for vilazodone. Further work is needed to understand the metabolic profile for vilazodone in children versus adults.

Electronic supplementary material

The online version of this article (10.1186/s12907-019-0084-9) contains supplementary material, which is available to authorized users.