# Sex and age differences of inflammatory biomarkers around a bloodstream infection: a population-based cohort study

## TL;DR

This study found that females, especially those over 50, have higher inflammatory responses than males during bloodstream infections.

## Contribution

The study reveals sex and age differences in inflammatory biomarker levels around bloodstream infections using population-based data.

## Key findings

- Females showed significantly higher peak CRP and neutrophil levels than males during bloodstream infections.
- The highest biomarker levels were observed in females aged 50 and older.
- Neutrophil levels were more similar between sexes but still higher in females over 50 after infection onset.

## Abstract

Few studies in humans have revealed differences in the inflammatory responses between biological sexes when encountering serious infections. Our study aimed to investigate how those differences were presented among sexes and age groups from 30 days before (D–30) through 30 days after (D30) a bloodstream infection (BSI).

We did a retrospective population-based cohort study, including patients aged > 15 years with their first-time BSI between 2007 and 2016.

Based on aggregated data, we computed daily mean levels of C-reactive protein (CRP) and neutrophils in the D–30/D30 period, separately for females and males within the age groups 15–49 and ≥ 50 years. For each age group, we used adjusted multilevel mixed effects linear regression analyses to detect differences in daily mean levels between females and males.

A total of 24,074 patients had 268,648 specimens with CRP and 138,482 with neutrophils. CRP and neutrophils peak values were significantly higher in females, reaching their highest values among the ≥ 50 years group. For all age groups, peak values occurred for CRP at D1 and for neutrophils at D0. Neutrophil values were more equal between the sexes, although higher levels were found in the ≥ 50 year age group among females after D–4.

Females and males with BSI exhibited different trajectories and different peak values close to the BSI episode, in particular in females in the ≥ 50-year age group. Severe infections, such as BSI, need further investigation regarding sex differences, stratified into age groups for expected female menopause.

The online version contains supplementary material available at 10.1007/s15010-026-02732-y.