Point: A Less Than Glowing Interpretation of Urine Fluorescence

by Jessica Shenoi, MD; Michael E. Mullins, MD; and Ari B. Filip, MD

We disagree with Dr. Hack’s recommendation for examining urine under ultraviolet (UV) light for suspected ethylene glycol ingestions.¹ This test is inherently unreliable with poor sensitivity, specificity, and accuracy (49 percent, 75 percent, and 59 percent, respectively).² Parsa, et al. found 100 percent of pediatric urine specimens fluoresced even in the absence of ethylene glycol. Other common substances, such as multivitamins and vitamin-fortified cereal may cause urine fluorescence.³ Casavant, et al. corroborated that most pediatric urine samples fluoresce under UV light and found considerable interrater variability.⁴ The urine containers themselves may contribute to fluorescence.

Parsa, et al. also tested different concentrations of sodium fluorescein in lactated Ringer’s solution.³ The minimum sodium fluorescein concentration to fluoresce reliably was 312 ng/mL. They calculated that this would require an ingestion of about 4 L of ethylene glycol in a 50 kg person.

A more useful indirect clue that Dr. Hack omitted is an extremely high apparent lactic acid concentration. Point-of-care (POC) analyzers rapidly measure lactate using lactate oxidase but cannot distinguish lactate from glycolate (the first acid metabolite of ethylene glycol). Several case reports (including one with no urine fluorescence) found apparent lactate concentrations exceeding 15 mmol/L (often exceeding 30 mmol/L.)^6-10 Simultaneous lactate measurement using lactate dehydrogenase typically reveals a “lactate gap”.^6-10

In a case with a clear history of antifreeze ingestion and an osmolal gap, we believe that the unreliable examination of the urine under UV light adds nothing to the diagnosis. If uncertainty remains while awaiting definitive testing, a POC lactate is a better clue.

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Dr. Shenoi is a third-year resident in emergency medicine at the University of Arkansas for Medical Sciences (UAMS) and will start her Medical Toxicology fellowship at Emory University later this year.

Dr. Mullins is a professor of emergency medicine and faculty member of the Medical Toxicology Fellowship at Washington University School of Medicine.

Dr. Filip is the medical director of the Arkansas Poison Center and faculty member in the emergency medicine residency at UAMS.

References

1. Hack J. An illustrated case of ethylene glycol, direct and indirect. ACEP Now. 2023;43(10):20-21.
2. Wallace, KL, Suchard JR, Curry SC, Reagan C. Diagnostic use of physicians’ detection of urine fluorescence in a simulated ingestion of sodium fluorescein–containing antifreeze. Ann Emerg Med. 2001;38(1):49–54. doi: 10.1067/mem.2001.115531.
3. Parsa T, Cunningham SJ, Wall SP, Almo SC, Crain EF. The usefulness of urine fluorescence for suspected antifreeze ingestion in children. Am J Emerg Med 2005;23:787-792. doi: 10.1016/j.ajem.2005.02.051.
4. Casavant MJ, Shah MN, Battels R. Does the fluorescent urine indicate antifreeze ingestion by children? Pediatrics. 2001;107:113-114. doi: 10.1542/peds.107.1.113.
5. Woo MY, Greenway DC, Nadler SP, Cardinal P. Artifactual elevation of lactate in ethylene glycol poisoning. J Emerg Med. 2003;25:289-293. doi: 10.1016/S0736-4679(03)00203-8.
6. Brindley PG, Butler MS, Cembrowski G, Brindley DN. Falsely elevated point-of-care lactate measurement after ingestion of ethylene glycol. CMAJ. 2007;176(8):1097-1099. doi 10.1503/cmaj.061288.
7. Verelst S, Vermeersch P, Desmet K. Ethylene glycol poisoning presenting with a falsely elevated lactate level. Clin Toxicol. 2009; 47:236–238. doi: 10.1080/15563650802432954.
8. Manini AF, Hoffman RS, McMartin KE, Nelson LS. Relationship between serum glycolate and falsely elevated lactate in severe ethylene glycol poisoning. J Anal Toxicol. 2009;33:174-176. doi: 10.1093/jat/33.3.174.
9. Pernet P, Bénéteau-Burnat B, Vaubourdolle M, Maury E, Offenstadt G. False elevation of blood lactate reveals ethylene glycol poisoning. Am J Emerg Med. 2009;27:132.e1-132.e2. doi:10.1016/j. ajem.2008.04.029.
10. Berg A, Tamama K, Peck-Palmer OM. Metabolic acidosis with discrepant lactate results. Clin Chem. 2013;59(4)713–721. doi: 10.1373/clinchem.2012.197939.

Counterpoint: Many Clues to Catch a Culprit

by Jason Hack, MD, FACEP, FACMT