Method Validation Study of Dipstick Urinalysis as a Screening Tool for Sodium Nitrite Toxicity

The incidence of suicide by intentional nitrite ingestion has increased since 2017. Limited options exist for commercial laboratory analysis for nitrite/nitrate. This study investigates the use of urine dipsticks for screening at autopsy for potential toxicity with sodium nitrite and, less commonly, alkyl nitrite. Archived samples of blood, urine, vitreous fluid, and gastric contents from 4 sodium nitrite/nitrate cases, 3 alkyl nitrite cases, and 4 control cases were tested using dipsticks. A rapid, strong positive result for nitrite was in the vitreous fluid of all 4-sodium nitrite/nitrate cases, along with 2 positive urine and 1 positive gastric. The 2 alkyl nitrite inhalation toxicity cases had no positive results. One alkyl nitrite ingestion case had a positive urine. The 4 controls had negative urine: equivocal results in 2 vitreous, and 1 positive gastric. Urine dipsticks are a useful adjunct to laboratory testing for nitrite toxicity and provide a rapid, cost-effective tableside result that may guide the need for further testing. Vitreous fluid and urine appear to be the most reliable specimens, although testing of gastric liquid may be useful to corroborate oral ingestion. Dipsticks may not be a reliable adjunct for testing for alkyl nitrite toxicity via inhalation route, likely due to the much lower nitrite concentration compared to nitrite ingestion cases.