Predictive value of urine microscopy and urine culture in bacteraemic adults without localising urinary features

Urine microscopy (UM) and urine culture (UC) are used in bacteraemic patients to identify a urinary focus of infection. However, their positive and negative predictive values (PPV and NPV) in patients without localising urinary features are uncertain.

We aimed to determine the predictive value of UM/UC for diagnosing bacteraemic urinary tract infection (bUTI) in bacteraemic patients without localising urinary features.

A retrospective study of bacteraemic adults was conducted. PPV and NPV of UM/UC for bacteraemic urinary tract infection (bUTI) was determined in two subgroups of patients without localising urinary features: those with an unclear focus of infection, and those with a suspected non-urinary focus of infection. In those with an unclear focus, univariate analysis for risk factors associated with bUTI was performed.

A total of 871 patients were included. Localising urinary features were absent in 110 of 342 patients (32.2%) with bUTI. In patients with an unclear focus, UM had a PPV of 51.5% and an NPV of 96% for bUTI, and UC had a PPV of 75% and an NPV of 88.6%. In patients with a suspected non-urinary focus, UM had a PPV of 5.2% and an NPV of 100%, and UC had a PPV of 25% and an NPV of 99.5%. While some risk factors for bUTI in patients with an unclear focus were identified, 22 of 98 patients (22.4%) had bUTI despite no risk factors.

bUTI without localising urinary features is common. In bacteraemia of unclear focus, UM/UC has a high NPV for excluding bUTI, although PPV is limited and non-urinary foci require consideration despite a positive result. UM/UC is low yield in those with a suspected non-urinary focus of infection.