Trending of a falsely elevated serum creatinine after a pediatric nitromethane ingestion: A case report

Abstract

Introduction: Nitromethane is a primary nitroalkane used as a solvent and a fuel that may be toxic by ingestion, inhalation, or contact. Its presence can be detected in serum of exposed persons, but levels are not readily available to guide patient care. Nitromethane has been shown to falsely elevate serum creatinine when clinical laboratories use Jaffe assays to measure creatinine; enzymatic assays are not affected. Ex vivo experiments have demonstrated a linear relationship between serum nitromethane and the elevation in Jaffe assay creatinine. This case report demonstrates an elevation of creatinine measured by Jaffe assay with normal creatinine measurement by enzymatic assay after exposure to nitromethane.

Case report: A 21-month-old girl ingested an unmeasured quantity of a hobby fuel, a fuel containing methanol, nitromethane (20%), and lubricants used in miniature internal combustion engines, such as remote-controlled cars. She was initially evaluated at a community hospital, treated empirically for methanol toxicity with fomepizole and folic acid, and transferred to a university hospital for further management. By 19 hours after ingestion, methanol was below detection, but a serum creatinine of 2.63 mg/dl raised concern for kidney injury. Toxicology consultation recognized that the creatinine had been measured using a Jaffe assay and recommended a repeat creatinine using an enzymatic assay, which was within normal limits. The patient remained an inpatient for further evaluation, which permitted trending of her Jaffe assay creatinine over a 3-day period. The Jaffe assay creatinine demonstrated a gradual decline; repeat enzymatic assay creatinine remained within normal limits.

Discussion: The decline in this pediatric patient's Jaffe assay creatinine is consistent with first-order clearance of nitromethane, which has been previously described in adult exposures. This case demonstrates how Jaffe assay-derived serum creatinine may be useful in the pediatric population to establish, quantify, and trend nitromethane exposure with essential concurrent use of an enzymatic assay to determine actual creatinine.

Keywords: Jaffe assay; creatinine; enzymatic assay; falsely elevated creatinine; ingestion; nitromethane; pediatric.

FIGURE 1

Serum creatinine (mg/dl) (left vertical axis) obtained using Jaffe assay (closed circles) and obtained using enzymatic assay (closed triangles) for the 21‐month‐old girl in this case report from time of ingestion of the hobby fuel with estimated corresponding serum nitromethane (right vertical axis) for the Jaffe assay creatinine (closed circles) based on a previously determined conversion factor

FIGURE 2

Comparison over time of Jaffe assay serum creatinine (mg/dl) (closed circles) obtained from the 21‐month‐old girl in this case report with Jaffe assay serum creatinine (mg/dl) (open circles) obtained from a previously reported case involving a 25‐year‐old male patient who sustained a nitromethane exposure (by contact and likely inhalation)

FIGURE 3

Natural log of the Jaffe assay serum creatinine of the 21‐month‐old girl in this case report (closed circles) and of the 25‐year‐old male patient (open circles) over time, demonstrating the linearity expected of first‐order clearance of nitromethane. Calculated half‐life is 26 hours for the 21‐month‐old girl and 35 hours for the 25‐year‐old male patient