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

Background: 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.

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

Methods: 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.

Results: 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.

Conclusions: 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.