2025. Procalcitonin Reference Cutoff and Specimen-Type Validation

INVESTIGATION: The primary objective of this study was to validate that the clinical cutoff of 0.3 ng/mL is appropriate in our population of patients. The secondary objective of this study was to compare procalcitonin results in plasma and serum specimens to prove that both sample types gave similar results. BACKGROUND: Our institution started performing procalcitonin testing on November 29, 2017. The Roche package insert indicated that in a population of 282 self-reported healthy individuals, the 95th percentile, upper reference range limit was calculated at 0.08 ng/mL. This 95th percentile cutoff seemed to be much lower than published clinical cutoffs of 0.25 and 0.30 ng/mL. Upon extensive literature review and discussion with pediatric and adult infectious disease physicians, we decided to use the clinical cutoff of 0.3 ng/mL to indicate invasive bacterial infection in our institution. METHODS: Two hundred and fifty patients with normal renal and hepatic function, white blood cell counts and C-reactive protein below 5.0 mg/L were selected for the validation of procalcitonin clinical cutoff. An additional 100 patients with paired plasma and serum specimens drawn at the same time were selected for the plasma vs. serum comparison study. All results were analyzed using the R statistical program. RESULTS: Blood specimens from 128 females and 122 male patients ranging from 10 to 84 years old were utilized in this study. Out of the 250 specimens, 128 were plasma and 122 were serum specimens. The procalcitonin 95th percentile upper reference range limit based on our population was 0.08 ng/mL, which validated the Roche package insert claim. Only one out of 250 patients (0.4%) had procalcitonin result above 0.3 ng/mL. The paired plasma and serum specimens in 100 patients yielded procalcitonin results that correlated with a Pearson’s R value of 0.999. The linear regression equation for the correlation was y = 0.94x. CONCLUSION: This result confirmed that a procalcitonin clinical cutoff of 0.3 ng/mL is appropriate in our patient population. It also showed that both plasma and serum specimens can be used for procalcitonin measurement. DISCLOSURES: M. Ahmad, Roche: Collaborator, Research support. A. Adaya, Roche: Collaborator, Research support. D. Patel, Roche: Collaborator, Research support. R. Benirschke, Roche: Collaborator, Research support. H. Lee, Roche: Collaborator, Research support.