B-317 Poor Standardization of Specimen Validity Tests Leads to Significant Variation of Urine Adulteration Positivity Rates
Authors: Fatica E M , Ksiazek L R , Koch C D 
Published: September 2023

Background

Drugs of abuse testing is performed in multiple settings including pain management, pre-transplant evaluations, and employment screening. It is important to be able to accurately assess the integrity of urine specimens to detect efforts to mask the presence of drugs through dilution, substitution, or other means of adulteration (e.g., adding bleach or other chemicals). These detection methods, however, are not standardized and therefore adulteration detection performance may vary widely. The purpose of this study was to compare several specimen validity testing (SVT) methods.

Methods

Results for SVT testing performed in January 2023 were retrospectively reviewed for urine specimens submitted for occupational drug testing (ODT) or for which comprehensive drug screening (CDS) was ordered. Specimens screening positive or near the cut-offs for adulteration/dilution by UrineCheck®7 (UC7) test strips (creatinine, specific gravity (SG), pH, bleach, pyridinium chlorochromate (PC), nitrites, glutaraldehyde) or the Thermo DRI® (SG, pH, oxidants) and Beckman creatinine assays were included in the study. Additional testing by the Roche Cobas Pro SVT assays (creatinine, SG, pH, oxidants, nitrites, chromate), pH meter (Fisher accumet AB315) and SG refractometer (Reichert® Goldberg TS Meter) was performed (n = 7 ODT, 22 CDS). Nitrite-positive specimens submitted for routine urine analysis (UA) (n = 6) were also included to assess each assay’s interference potential (i.e., false positive) from nitrites produced from urinary tract infections.

Results

Of the 244 ODT results, 5 were “dilute” and 7 were positive for bleach, PC and/or nitrites by UC7 test strips. There were 603 CDS results, of which 23 had a urine creatinine &lt;20 mg/dL but only 6 of these also had a low SG (&lt;1.003) by DRI assays. Only one specimen was flagged for low pH by all methods except the DRI assay. Of the 5 ODT specimens that were positive for bleach and PC by UC7, none exceeded the cutoffs when tested on the DRI oxidant (100 µg/mL), Roche oxidants (200 mg/L), or Roche nitrites (500 mg/L) assays, however these specimens did have higher values than the other specimens in the ODT group for all assays. The UC7 assay was the most sensitive for oxidant detection although this study was not designed to differentiate true from false positive results. The Roche assay was the most sensitive to urinary tract infection-related nitrites although values were still well below the positive cutoff (Mean ± SD = 46.7 ± 11.1 mg/L). Surprisingly, pH had poor agreement among methods but good overall concordance. For the assessment of specimen dilution, creatinine values correlated well but specific gravity generally did not. Additionally, overall concordance was poor (14/35 specimens) when manufacturer-specific cutoffs were applied. Notably, cutoffs varied greatly between assays which likely contributed to the poor concordance more so than the variation in measured values.

Conclusion

These findings suggest that the choice of urine SVTs can have a significant impact on positivity rate due to the lack of standardization. While we have determined that sensitivity and specificity varies significantly between assays, further studies are needed to evaluate method accuracy and overall adulteration detection performance.