MSACL 2025 Abstract

Enhancing Toxicology Clinical Consultation through Retrospective Analysis of Preliminary Positive Immunoassay-Based Urine Drug Screening Results

Sheng-Ying Lo
Geisinger Medical Center, Danville, PA

Sheng-Ying Lo (Presenter) Geisinger Medical Center

Relevant Financial Disclosures (within past 24 months, reported on Jul 17, 2025) No relevant financial relationship(s) to disclose. Conflict mitigation NOT REQUIRED.

INTRODUCTION:
Urine drug testing is an important tool in clinical toxicology for detecting and monitoring substance exposure. Advancements in mass spectrometry (MS) have significantly improved the sensitivity and specificity of urine drug testing by reducing false positives and false negatives. Despite these advancements, immunoassay-based urine drug testing remains widely used in clinical laboratories due to its lower cost, faster turnaround time, and adaptability for automation. Understanding the performance of immunoassay-based drug screens in a patient-specific population is valuable for aiding clinicians to make rapid, better-informed decisions.

OBJECTIVE:
This study aims to evaluate the accuracy of preliminary positive screening results to enhance toxicology consultation. This is particularly important in clinical situations where timely patient management and treatment decisions are needed before MS confirmation results are available.

METHODS:
Immunoassay and MS confirmatory results generated over four years within a rural health system from a urine drug screening panel with reflex to MS confirmation of positive screens only (N = 55,054) were queried for analysis. Positive screening results with subsequent drug/drug metabolite(s) present above the quantitation cutoffs of MS-based assays were defined as true preliminary positives. Positive predictive value (PPV) was determined for six specific screening assays that remained consistent throughout the retrospective analysis period. Data were further divided into age groups: 0 to 11 years (Group 1), 12 to 19 years (Group 2), and 20 years and older (Group 3), to determine the PPVs for pediatric and adult populations when the number of results in the group exceeded 20.

RESULTS:
The overall PPV for the amphetamines screen is 77.3% (N = 5358), the cannabinoids screen is 98.3% (N = 11946), the cocaine metabolite screen is 96% (N = 1075), the methadone metabolite screen is 96% (N = 1112), the opiates screen is 98.4% (N = 4564), and the oxycodone screen is 98.2% (N = 5845). Stratifying the amphetamines screen by age group showed a PPV of 95.6% (N = 45) for Group 1, 81.4% (N = 156) for Group 2, and 77% (N = 5157) for Group 3. The PPV of the cannabinoids screen also differed between pediatric and adult populations. Stratifying the cannabinoids screen by age group showed a PPV of 50% (N = 60) for Group 1, 98.1% (N = 930) for Group 2, and 98.6% (N = 10956) for Group 3. The remaining immunoassay-based screens showed minimal variation in PPV among the different age groups.

CONCLUSION:
Based on this retrospective analysis, five out of six immunoassay-based urine drug screens showed a high likelihood of preliminary positive results being confirmed by MS-based testing, except for the amphetamines screen. Notably, while the amphetamines screen performed well in the younger pediatric patients, its reliability declined with increasing age. In contrast, the cannabinoids screen was less reliable in the younger pediatric populations, indicating that alternative methods — such as umbilical cord tissue or meconium testing — may be more suitable for detecting in utero cannabinoid exposure. Overall, this study highlights the value of evaluating immunoassay screen performance within specific patient populations to inform clinical decision-making when MS confirmation is in progress.