# Metabolic acidosis is associated with infection severity in pediatric pyelonephritis and pneumonia

## TL;DR

Metabolic acidosis is more common and severe in children with kidney infections compared to pneumonia, and it correlates with disease severity.

## Contribution

This study establishes a link between metabolic acidosis and infection severity in pediatric pyelonephritis and pneumonia.

## Key findings

- Metabolic acidosis occurred in 84% of pyelonephritis and 66% of pneumonia patients.
- Lower bicarbonate levels correlated with longer hospital stays and more fever days in pyelonephritis.
- Anion gap acidosis was more prominent in pneumonia patients compared to pyelonephritis.

## Abstract

Pyelonephritis is the most common serious bacterial infection in pediatric patients. Several electrolyte abnormalities have been described with pyelonephritis, including metabolic acidosis. We sought to describe the frequency and clinical significance of metabolic acidosis in pediatric patients with acute Escherichia coli (E. coli) pyelonephritis, with comparison to parallel infection group of bacterial pneumonia.

This was a single-center, retrospective study of pediatric patients with pyelonephritis or pneumonia hospitalization. Nadir serum bicarbonate and anion gap values were collected, and baseline and recovery values when available. Serum electrolyte and creatinine values and markers of infection severity were recorded.

Ninety-four pyelonephritis and 95 pneumonia subjects were included. Pyelonephritis mean nadir bicarbonate was 20 (SD 3) mEq/L, statistically significantly lower than 21 (3) mEq/L in pneumonia. Corresponding anion gap was 16 (4) mEq/L in pyelonephritis, statistically significantly lower than 17 (3) mEq/L in pneumonia. There was significant correlation between acidosis and number of fever days in pyelonephritis and between acidosis and hospital length of stay in both groups.

This study demonstrated development of acidosis in 84% of patients with pyelonephritis and in 66% with pneumonia. The mechanism of acidosis appears to have a greater contribution from elevated anion gap in the pneumonia group compared to the pyelonephritis group. Lower nadir serum bicarbonate values are associated with longer hospital length of stay in both groups and greater number of fever days in the pyelonephritis patients.

A higher resolution version of the Graphical abstract is available as Supplementary information

A higher resolution version of the Graphical abstract is available as Supplementary information

The online version contains supplementary material available at 10.1007/s00467-025-06708-2.