# Correlation between locally versus centrally processed serum procalcitonin during emergency department research evaluation of febrile infants aged 0–60 days

## TL;DR

This study shows that procalcitonin levels measured locally or at a central lab in febrile infants are highly consistent, making central testing a reliable option for research.

## Contribution

The study demonstrates that multiple local PCT assays correlate well with a central reference lab, even after freezing and shipping.

## Key findings

- Locally measured PCT levels showed strong correlation (ρ = 0.83) with central lab results.
- The average relative difference between local and central PCT measurements was 0.02%.
- Central lab testing after freezing is a reliable alternative when local testing is not possible.

## Abstract

Procalcitonin (PCT) is a useful biomarker in the initial evaluation of febrile infants for serious bacterial infections (SBIs). However, PCT is not always available locally and must at times be frozen and shipped to a reference laboratory for research studies. We sought to compare PCT measured locally versus centrally at a reference laboratory during a research study.

This was a secondary analysis of a multicenter study of febrile infants ≤60 days evaluated for SBIs from June 2016 to April 2019. A PCT cutoff value of 0.5 ng/mL was used to stratify infants at low-versus high-risk of SBIs. Statistical analyses consisted of Spearman's correlation, Bland-Altman difference plotting, Passing-Bablok regression, Deming regression, and Fisher's exact testing at the 0.5 ng/mL threshold.

241 febrile infants had PCT levels measured both locally and at the reference laboratory. PCT levels measured locally on 5 different platforms and from the frozen research samples demonstrated strong Spearman's correlation (ρ = 0.83) and had similar mean PCT values with an average relative difference of 0.02%. Eleven infants with SBIs had PCT values < 0.5 ng/mL in both the clinical and research samples. Six other infants had differences in SBI prediction based on PCT values at the 0.5 ng/mL threshold between the clinical and research platforms.

We found no significant differences in detection of febrile infants at high risk for SBI based on locally (on multiple platforms) versus centrally processed PCT. Testing at a central reference laboratory after freezing and shipping is an accurate and reliable alternative for research studies or when rapid turnaround is not required.

•Procalcitonin (PCT) is an important biomarker for serious bacterial infection (SBI).•Multiple PCT assays strongly correlated with a single reference laboratory assay.•Strong performance remained at the 0.5 ng/mL clinical decision threshold for SBI.•Use of a central laboratory is reasonable when analyses cannot be performed locally.

Procalcitonin (PCT) is an important biomarker for serious bacterial infection (SBI).

Multiple PCT assays strongly correlated with a single reference laboratory assay.

Strong performance remained at the 0.5 ng/mL clinical decision threshold for SBI.

Use of a central laboratory is reasonable when analyses cannot be performed locally.