Clinical usefulness of urine Gram stain for diagnosing urinary tract infections at the emergency department.

BACKGROUND

Diagnosis of urinary tract infections (UTIs) is a frequent challenge at the emergency department (ED). The clinical usefulness of the urine Gram stain (GS) is uncertain.

OBJECTIVE

We studied the GS performance to clarify its clinical utility at the ED.

METHODS

Urine dipstick (UD), automated urinalysis (UF-1000), GS and urine culture (UC) were performed in a cohort of consecutive adults presenting at the ED suspected of a UTI. GS performance was assessed and compared to UD and UF-1000

RESULTS

A UTI diagnosis was established in 487/1358 (35.9%) episodes. Sensitivity and specificity for 'many' GS leucocytes was 33.7% and 95.4%; for 'many' GS bacteria 51.3% and 91.0%. GS diagnostic performance by ROC analysis was 0.796 for leucocytes and 0.823 for bacteria. GS bacteria performed better than UD nitrite comparable to UF-1000 bacteria. GS leucocytes underperformed compared to UD leucocyte esterase and UF-1000 leucocytes. UC was positive in 455 episodes. GS correctly predicted urine culture of gram-negative rods (PPV 84.6%). Prediction was poor for gram-positive bacteria (PPV 38.4% (cocci), 1.0% (rods)).

CONCLUSION

With the exception of a moderate prediction of gram-negative bacteria in the UC, urine GS does not improve UTI diagnosis at the ED compared to other urine parameters.