The diagnostic utility of procalcitonin is limited in the setting of methamphetamine toxicity

Procalcitonin (PCT) is a biomarker with greater specificity for bacterial infection than other current laboratory markers. However, PCT can also be elevated in the setting of several noninfectious conditions. A recent case report describes a patient with elevated PCT in the context of acute methamphetamine intoxication, but without evidence of infection. Thus far, no studies have evaluated the diagnostic utility of PCT in patients with active methamphetamine use. We seek to test the hypothesis that PCT has diminished utility in patients who use methamphetamine presenting to the Emergency Department (ED). We performed a retrospective cohort study of patients presenting to an academic ED between May 2017 and July 2019. We included patients ≥18 years of age with a positive urine methamphetamine test and at least two PCT results. Pregnant patients were excluded. Cases were classified as microbiologically documented infection, clinically documented infection, possible infection, or no infection by clinician review. A positive PCT value was defined as ≥0.5 ng/ml. The performance of PCT as a diagnostic test for bacterial infection in this population was then evaluated using sensitivity, specificity, false positive rate, false negative rate, and area under the receiver operating characteristic curve. We identified 143 patients, including 75 with recorded PCT levels ≥0.5 ng/ml and 93 with microbiologically or clinically documented bacterial infection. The sensitivity and specificity of PCT for bacterial infection in this study population was 60% and 64%, respectively. The false positive rate was 36% while the false negative rate was 40%. The area under the ROC curve was 0.65. Additionally, we describe 8 patients with confirmed absence of infection but with elevated PCT, 4 of whom had serum values >10 ng/ml. The results suggest that PCT has poor diagnostic utility for bacterial infection in patients with active methamphetamine use presenting to the ED.