Renal concentrating capacity in female outpatients with symptomatic urinary tract infection

Renal concentrating capacity (RCC) has been used as a tool in the diagnosis of the site of urinary tract infection (UTI). In this study, RCC was measured in women with symptoms of UTI in relation to the clinical picture and the bacterial species isolated.

In 633 outpatients aged > or =18 years with symptoms of UTI, a renal concentration test with desmopressin was performed at baseline. The test was repeated after antibiotic treatment in a subset of patients with osmolality values below the reference levels at entry. The bacterial species were identified and patients were classified as having either pyelonephritis or cystitis.

RCC was reduced in patients infected with Escherichia coli or Staphylococcus saprophyticus compared to those who had negative urine cultures and increased after antibiotic treatment. Patients with symptoms of both pyelonephritis and cystitis had reduced RCC: 44/68 (65%) and 205/457 (45%), respectively.

These findings demonstrate a considerable overlap in RCC between patients with pyelonephritis and cystitis, making the osmolality test unreliable for the purpose of diagnosis of the site of UTI.