Urinary retinol excretion and kidney function in children with shigellosis

Background: Acute infections, including diarrhea, are associated with an increased risk of vitamin A deficiency. Urinary retinol excretion during such infections may contribute to this risk. The mechanism accounting for urinary retinol loss has not been clearly defined. Objective: This study attempted to determine whether urinary retinol loss in children with acute infection is associated with impaired kidney function, particularly impaired tubular protein reabsorption. Design: Urinary retinol excretion and kidney function were examined in 66 hospitalized children 5 mo to 5 y of age with acute Shigella dysentery. Results: Urinary retinol loss occurred in 59% of children and was substantial (>0.1 μmol/d) in 8% of them. Children with more severe disease excreted higher concentrations of urinary retinol; those with a body temperature ≥40°C excreted a mean of 0.10 ± 0.18 μmol/d compared with 0.005 ± 0.008 μmol/d for other children (P < 0.0001). Children with more severe disease also had impaired tubular reabsorption of low-molecular- weight proteins [β₂-microglobulin and retinol binding protein (RBP)], although other measures of tubular and glomerular function were not similarly impaired. In multiple regression analysis, severity of disease indicators were the best predictors of tubular reabsorption of β₂-microglobulin (R² = 0.53) whereas tubular reabsorption of β₂-microglobulin and RBP were found to be the best predictors of urinary retinol loss (R² = 0.69). Conclusions: A significant amount of retinol was excreted in the urine in children with shigellosis: 8% excreted >0.10 μmol/d (15% of the daily metabolic requirement). Impaired tubular reabsorption of low-molecular-weight proteins, such as RBP transporting retinol, appeared to be the cause of this urinary retinol loss.