C-Reactive Protein Trajectories by Summary Metric Across the Coronavirus-2019 Period: A 16-Year Interrupted...

Background/Objectives: The clinical utility of summarizing long-term C-reactive protein (CRP) trends with a single mean remains unclear. We systematically characterized annual changes in CRP test volume and CRP level distributions using large-scale laboratory data collected at Dankook University Hospital (2008-2023) across the coronavirus 2019 pandemic period. Methods: Overall, 1,845,258 CRP values were analyzed; annual arithmetic, harmonic, and geometric means were calculated; long-term trends were assessed using weighted least squares (WLS) regression weighted by annual test volume; and temporal changes around the pandemic period were examined using a WLS-based interrupted time-series (ITS) segmented model with a prespecified 2020 break. Results: The annual test volume rose from 2008 to 2013 and 2019, dropped in 2020, increased in 2022, and declined in 2023. The arithmetic mean showed no long-term trend, whereas the harmonic and geometric means declined. ITS models exhibited no statistically significant immediate level-change term in 2020; however, post-2020 slope changes indicated a decline in the arithmetic mean and attenuation of the prior decline in the harmonic mean. As only four annual observations were available after 2020, these post-2020 trend estimates should be interpreted cautiously. Conclusions: Within this single-center tertiary-care dataset, different CRP summary measures showed different long-term patterns and post-2020 trend changes, without evidence of an abrupt shift in 2020, suggesting stratum-specific shifts that may be invisible to arithmetic mean-based surveillance. These findings are best interpreted as institution-specific and hypothesis-generating, and broader interpretive or operational implications require validation in multicenter settings with differing case-mix and care structures.