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. 2025 Apr 9;13(1):e44.
doi: 10.22037/aaemj.v13i1.2619. eCollection 2025.

Performance of Gram Stain, Leukocyte Esterase, and Nitrite in Predicting the Presence of Urinary Tract Infections: A Diagnostic Accuracy Study

Carlos Solorzano  1 , Maria Camila Rubio  1 , Maricel Licht-Ardila  1 , Camila Castillo  1 , Juan Camilo Valencia Silva  1 , Maria Alejandra Caro  1 , Edgar Fabián Manrique-Hernández  1 , Alexandra Hurtado-Ortiz  1   2 , Liliana Torcoroma García  2
Affiliations

Performance of Gram Stain, Leukocyte Esterase, and Nitrite in Predicting the Presence of Urinary Tract Infections: A Diagnostic Accuracy Study

Carlos Solorzano et al. Arch Acad Emerg Med. .

Abstract

Introduction: While urine culture is the gold standard for the urinary tract infection (UTI) diagnosis, delays in results highlight the need for rapid tests. This study aimed to evaluate the accuracy of urine Gram staining, leukocyte esterase, and nitrite in predicting the presence of UTI.

Methods: A cross-sectional diagnostic accuracy study was conducted on adult patients undergoing urine culture at a high-complexity hospital in northeastern Colombia. The results of Gram staining and urinalysis (nitrite and leukocyte esterase) were compared to urine culture as the gold standard test, and screening performance characteristics were calculated and reported for individual and combined tests.

Results: A total of 2,123 urine cultures were analyzed, with 49.8% testing positive. Escherichia coli was the most common pathogen (24.7%), and 76.17% of patients received antibiotics, primarily ceftriaxone (38.7%). Gram staining showed 56.9% (95% confidence interval (CI)=54.4 to 59.4) sensitivity and 76.8% (95% CI=72.6 to 80.5) specificity, leukocyte esterase had 67.9% (95% CI= 65.3 to 70.4) sensitivity and 84.5% (95% CI=81.4 to 87.2) specificity, and nitrite demonstrated the highest sensitivity (85.3%, 95% CI=82.0 to 88.2). The combination of Gram staining (+), leukocyte esterase (+), and nitrite (+) achieved 87.6% (95% CI=84.2 to 90.5) sensitivity and 94.6% (95% CI=93.1 to 95.9) negative predictive value (NPV), with the decision tree identifying this combination as having the highest diagnostic utility (positive likelihood ratio (PLR) = 23.77, 95% CI=18.34 to 30.80).

Conclusions: It seems that, integrating urine Gram staining with leucocyte esterase and nitrite improves UTI diagnosis in high-complexity emergency settings, reducing unnecessary urine cultures and antibiotic use while enhancing resource utilization and mitigating bacterial resistance.

Keywords: Diagnostic tests; Nitrites; Sensitivity and specificity; Urinalysis; Urinary tract infections; routine.

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Conflict of interest statement

The authors declare no financial conflicts of interest or personal relationships that may have influenced the work presented in this article.

Figures

Figure 1
Figure 1
Area under the receiver operating characteristic (ROC) curve of the three studied tests in predicting the presence of urinary tract infection.
Figure 2
Figure 2
Decision tree for evaluating the diagnostic utility of the three tests. Decision tree illustrating the diagnostic utility of Gram staining, leukocyte esterase, and nitrite for evaluating suspected urinary tract infections. Likelihood ratios (LRs) adjacent to the test boxes represent individual test performance, while LRs along the connecting lines indicate the combined diagnostic performance of sequential tests.
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