NDT Plus (2008) 1: 30–31 doi: 10.1093/ndtplus/sfm018 Advance Access publication 19 December 2007 Case Report

Nitromethane-containing fuel toxicity causing falsely elevated serum creatinine

Satish Patel1, Sudharani Dikkala2 and Richard J Marcus1

1Division of Nephrology and Hypertension, Allegheny General Hospital, West Penn Allegheny Health System, Pittsburgh, PA, USA and 2Department of Internal Medicine, Allegheny General Hospital, West Penn Allegheny Health System, Pittsburgh, PA, USA

Keywords: creatinine; fuel; methanol; nitromethane urea nitrogen (BUN) 6 mg/dl, creatinine 0.6 mg/dl and serum osmolality 275 mOsm/kg. Arterial blood gas results: pH 7.314, pCO2 42, pO2 202, SaO2 95%, HCO3 20.8. Urine drug screening was positive for cannabinoids and benzodi- Introduction azepines. Due to the elevated methanol level, the patient was treated with fomepizole at the outside hospital. She was not Nitromethane (CH3NO2) ingestion is not known to cause given any charcoal and was transferred to our hospital for significant morbidity or mortality. Nitromethane is a com- further care. Laboratory data on presentation to our hospi- mon component of model airplane fuel or rocket fuel along tal revealed a BUN of 7 mg/dl, creatinine of 14.1 mg/dl, an with methanol. It has been reported that nitromethane anion gap of 16 and osmolar gap of 44. Patient was dialysed exposure can cause false elevation of the serum creati- due to clinical deterioration and an elevated methanol level. nine level when using the common Jaffe reaction method Post-dialysis creatinine dropped to 6.9 mg/dl and returned of analysis [1,2]; however this is not clinically well to 1.6 mg/dl by hospital Day 7 without any further dialysis known. The standard assay for the measurement of cre- treatments. atinine is based on the Jaffe reaction, in which alkaline Nitromethane is used commonly as a fuel additive along sodium picrate reacts with creatinine to form an orange- with methanol for race cars, boats and model engines. Acute red color. There are many substances known to interfere ingestion of nitromethane is not known to cause significant with the Jaffe assay, the most important being acetoac- morbidity, but it is a topical irritant. Nitromethane is highly etate, cephalosporins, bilirubin, ascorbic acid pyruvate and lipid-soluble, which may account for the relatively long dopamine. elimination over several days. Isolated nitromethane expo- sure requires only supportive care with no specific ther- apy. None of the common laboratory tests or toxicology Case report screens can detect nitromethane. Nitromethane interferes with the routinely used Jaffe reaction in the measurement A 38-year-old woman with a history of substance abuse of serum creatinine. These assays involve the interaction of presented to the emergency department of an outside creatinine with alkaline picrate and subsequent monitoring hospital. She had consumed an unknown quantity of syn- of changes in absorbance between 500 nm and 530 nm. thetic model engine fuel that contained methyl alcohol and Nitromethane contains a reactive methyl group, which nitromethane. Her initial vital signs included a heart rate reacts with alkaline picrate to produce a cromophore with of 97 beats per minute, respiratory rate of 16 breaths per a pattern of absorbance across the spectrum that closely re- min, blood pressure 130/90 mmHg and oxygen saturation of sembles the creatinine–picrate complex, creating a falsely 100% on a non-rebreather mask. The patient’s clinical con- elevated creatinine level. Known potential sources of inter- dition deteriorated and she became obtunded in the emer- ference with the Jaffe reaction include ascorbic acid, ace- gency department, requiring intubation and mechanical tone, bilirubin, ketoacids and drugs such as cephalosporins ventilation. Her initial laboratory data included a methanol and dopamine. These substances generally produce mild el- level of 102 mg/dl, ethanol level <10, salicylate level evations and may double the apparent creatinine. Enzymatic <1.0, acetaminophen level <10, ethylene glycol level and assay of creatinine, while not as widely used as the Jaffe isopropanol level were undetectable, anion gap 12, blood reaction, renders accurate measurement of creatinine in the presence of nitromethane. We should caution that enzyme- Correspondence and offprint requests to: Satish Patel, Division of based creatinine assays are not free from drug-related inter- Nephrology and Hypertension, 4th Floor, South Tower, 320 East North Avenue, Pittsburgh, PA 15212-4772, USA. Tel: +1-412-359-3320; ference. We note that our patient’s initial creatinine was Fax: +1-412-359-4136; E-mail: [email protected] 0.6 mg/dl and increased to 14.1 mg/dl in a few hours,

C The Author [2007]. Published by Oxford University Press on behalf of ERA-EDTA. All rights reserved. For Permissions, please e-mail: [email protected] Nitromethane-containing fuel toxicity causing falsely elevated serum creatinine 31 which might be due to absorption of nitromethane in the References blood. Nitromethane is a component of fuels for race cars 1. Mullins ME, Hammett-Stabler CA. Intoxication with nitromethane- containing fuels: don’t be “fueled” by the creatinine. J Toxicol Clin and model aircraft. Although nitromethane produces dra- Toxicol 1998; 36; 315–321 matic elevations in creatinine concentrations using the Jaffe 2. De Leacy EA, Brown NN, Clague AE. Nitromethane interferes in reaction, these elevations are due to assay interference and assay of creatinine by the Jaffe reaction. Clin Chem 1989; 35: 1772– do not indicate renal dysfunction. Falsely elevated mea- 1774 surement of serum creatinine in patients with methanol and 3. Booth C, Naidoo D, Roseenberg A. Elevated creatinine after inges- nitromethane co-ingestion is significant. The false mea- tion of model aviation fuel: interference with the Jaffe reaction by surement can lead to unnecessary treatment interventions nitromethane. J Pediatr Child Health 1999; 5: 503–504 4. Leonard Charlene P, Akhtar J. Co-ingestion of methanol and such as sedation, insertion of central venous catheter, ad- nitromethane: using falsely elevated creatinine as indicator for ministration of unnecessary medication and even dialysis. methanol antidote use. Pediatr Crit Care Med 2007; 8: 392– Some of these treatment modalities could have serious con- 393 sequences. Management of the methanol intoxication takes 5. Michael JB, Sztajnkrycer MD. Deadly pediatric poisons: nine common precedence over concerns about the nitromethane in the agents that kill at low doses. Emerg Med Clin North Am 2004; 22: combined methanol–nitromethane exposure. Nitromethane 1019–1050 ingestion needs to be considered for patients with elevated 6. Kroll MH, Roach NA, Poe B et al. Mechanism of interference with the Jaffe reaction for creatinine. Clin Chem 1987; 33: 1129–1132 creatinine and toxic ingestion. 7. Gabrielli A, Hammett-Stabler C. False elevation of serum creatinine following skin absorption of nitromethane complicates the clinical di- Conflict of interest statement. None declared. agnosis of rhabdomyolysis. Chest 1998; 113: 119–122

Received for publication: 30.10.07 Accepted in revised form: 6.11.07