Fig. 1

Kinetics and predictive value of procalcitonin and C-reactive protein in COVID-19 patients. a Serial values of procalcitonin (PCT, left panel) and C-reactive protein (CRP, right panel) in patients with COVID-19 who did not develop a secondary infection (n = 33). Data are aligned on the day of the start of COVID symptoms, which is designated day 0. The arrows indicate the median day of hospital admission (day 7, interquartile range [5–11]) and the median day of ICU admission (day 10, interquartile range [6–14]). Data are expressed as geometric means with 95% confidence interval. When biomarker variables were not measured daily, data were binned into bins spanning 2 days using a custom script made in R-studio v3.6.2 (www.r-project.org). If more than one value was present in these 2-day bins, the mean value was used. b Serial values of PCT (left panel) and CRP (right panel) in patients (n = 33) with COVID-19 who did develop (n = 33) or did not (n = 33) develop a secondary infection. Data are aligned on the day of secondary infection, which is designated day 0. For the “no secondary infection” group, data are aligned on the median day of infection in the “secondary infection” group (day 14 after ICU admission). Data are expressed as geometric means with 95% confidence interval. Data were binned into bins spanning 2 days (see a for details). The groups were compared using mixed-models analysis (time × group interaction factor) on log-transformed data. p values placed under graph titles reflect between-group differences over the entire time period (day − 10 until day 14). p values for day − 10 until day 0 and day 0 until day 14 are shown on the top left and right. c Receiver operating curve to illustrate sensitivity and specificity of PCT (left panel) and CRP (right panel) levels to predict secondary infection. Binned PCT/CRP data of day − 1 and day 0 were used (see a for details). Positive predictive value (PPV), negative predictive value (NPV), and incidence are provided for the depicted concentrations