Reference change value and measurement uncertainty of CRP, ferritin, procalcitonin, troponin I and BNP tests in COVID-19 monitoring: how much change matters?

Abstract

Objectives: This study was designed to determine the point of clinically significant change in consecutive measurements of high concentrations of C-reactive protein (CRP), ferritin, procalcitonin, troponin I, and brain natriuretic peptide (BNP) in patients diagnosed with COVID-19. Methods: The reference change value (RCV) for each analyte was estimated using the following formula:. The combined RCV was calculated using the mean CV value determined using different concentrations. Measurement uncertainty (MU) was estimated according to NordTest guideline. The root-mean-square (RMS) bias and nominal uncertainty values (uCref ) were calculated. Standard uncertainty (ubias) and combined standard uncertainty (u) were calculated using the formula RMSbias²+uCref² and √(uRW²+ubias²)/2, respectively. Expanded uncertainty (U) was obtained by multiplying u by a coverage factor.