Background Thiamine deficiency (TD) has been reported in critically ill patients, both adult and paediatric. The risk factors and the outcomes associated with the development of TD in intensive care unit patients are not established. We aimed to determine the incidence and the risk factors associated with TD in children during the first 10 days of stay in a paediatric intensive care unit (PICU).

Methods In a prospective cohort study, 202 children admitted to PICU had thiamine whole blood concentrations monitored on the first, 5th and 10th day of PICU stay. Age, thiamine intake, C-Reactive Protein, malnutrition (WHO growth standards), admission diagnosis, disease severity Paediatric Index of Mortality 2 (PIM2), furosemide and dialysis use were analysed as risk factors for TD. An HPLC-based method (high performance liquid chromatography) was used to measure whole-blood thiamin concentrations. The data were analysed using a Binomial Generalised Estimating Equations model, which includes the correlation between admission, 5th and 10th day responses.

Results TD incidence rate was 15% during the first 10 days of ICU stay; 56 cases (28%) cases were detected on admission and 4 new cases occurred during the follow up. Decreased thiamine concentrations were associated with C-Reactive Protein increase during the PICU stay (OR: -0.035; 95% CI: -0.06–0.008; p = 0.01), but not with malnutrition (p = 0.09).

Conclusions 1) TD incidence is frequent on admission and decreases during the ICU stay; 2) Systemic inflammation is associated with decreased thiamine concentrations upon admission and during the follow up.