Scripties UMCG - Rijksuniversiteit Groningen
English | Nederlands

The utility of Gram stain for the diagnosis of urinary tract infection in the emergency department

(2018) Bergen, R. van (Rik)

Background: Urinary tract infections (UTI) are very common. Accurate diagnosis depends on both the presence of symptoms and a positive urine culture (UC). The results of a urine culture are not immediately available. Therefore, urine screening tests are necessary. In our study we assessed diagnostic performance of urine Gram stain compared to other urine screening tests. We also studied the accuracy with which Gram stain can predict the type of bacterium in the UC. Methods: We studied a cohort of 297 consecutive cases (278 patients) that presented at the emergency department and for which a UC was performed. Diagnostic values of Gram stain, urine dipstick and automated urinalysis were determined, using either a positive UC (≥105 CFU/ml) or clinically relevant UTI as gold standard. Results: Out of 297 cases, 86 had a positive UC and 87 had clinically relevant UTI. Using a positive UC as gold standard, Gram stain at the lowest cutoff value had a sensitivity of 99% (95%-CI: 94-100) and a specificity of 55% (47-63). Area under the ROC curve for Gram stain was 0,91 (0,87-0,94) and 0,95 (0,93-0,98) for automated urinalysis. Gram stain for Gram-negatives and for Gram-positives had a high negative predictive value (NPV) for the presence of respectively Gram-negatives (NPV = 98% (95-99)) and Gram-positives (NPV = 100% (98-100) in the UC. Conclusions: Gram stain was not superior to automated urinalysis in screening for UTI. Because of its speed, automated urinalysis can act as the preferred test in the clinic. Gram stain can be used to rule out the presence of either Gram-negatives or Gram-positives in the UC. This can be used to guide antibiotic therapy.

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