A-246 Can CRP be used to rule in or rule out elevated procalcitonin concentrations in the emergency department?

Abstract Background C-reactive Protein (CRP) and procalcitonin (PCT) are commonly used sepsis biomarkers but have very different properties. PCT rises earlier, has a shorter half-life and is more specific for sepsis than CRP. It is however significantly more expensive. This study examined whether CRP measurement can be used to screen for the need for PCT measurement in emergency department patients. Methods This was a retrospective study of anonymized records of paired CRP and PCT requests from the emergency department during 2023. All testing was performed using Beckman Coulter AU 5800 (CRP) and Roche e601 (PCT). PCT results were interpreted using the 2023 AACC guidelines on PCT use (PCT0.1 ug/L: strongly discourage antibiotic use; PCT 0.1-0.25: discourage antibiotic use; PCT 0.26-0.5: encourage antibiotic use; PCT0.5: strongly encourage antibiotic use) and the ability of CRP to predict PCT exceeding the various cutoffs was calculated using Microsoft Excel and Analyse-It statistical add-on. Results There were 1645 paired results available. The CRP concentrations at 95% and 99% sensitivity and specificity levels for the various PCT cutoffs are shown in the table, together with the projected reductions in PCT testing volumes if PCT testing is restricted to samples with CRP within the ranges defined by the 95% or 99% sensitivity/specificity values. For example, from the table, for PCT0.1 ug/L cutoff at 95% confidence, subsequent PCT measurement on the sample is only performed if CRP is between 3.4 and 90.5 mg/L. Conclusions Limiting PCT measurements to samples with CRP concentrations inside ranges based on the PCT cutoff of interest and the appropriate confidence level (95% or 99%) can potentially reduce PCT testing by 20-40% in emergency department patients. For laboratories which perform CRP and PCT analysis sequentially on different platforms, this approach allows significant reductions in PCT test volumes while ensuring testing is performed in equivocal cases.