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Impact of urine concentration and automatic interpretation on sensitivity and specificity of Legionella BinaxNOW®
Camille Jacqueline1, Ghislaine Descours1,2,3, Anne-Gaëlle Ranc2
1Centre National de Référence des Légionelles, Hospices Civils de Lyon, Institut des Agents Infectieux, Lyon, France.
Purpose:
Urinary antigen tests (UATs) are widely used for rapid diagnosis of Legionnaires' disease (LD), primarily detecting Legionella pneumophila serogroup 1 lipopolysaccharide (LPS). Strategies, such as urine concentration, were shown to improve performance but mostly in retrospective studies.
Methods:
We evaluated the impact of urine concentration on the diagnostic sensitivity and specificity of the BinaxNOW® assay. A set of 90 positive and 200 negative urine samples were prospectively collected. Another set of 48 positive urine samples were selected retrospectively to evaluate both urine concentration but also automated interpretation using the Digival™ reader on test sensitivity and specificity.
Results:
We found that urine concentration significantly increased sensitivity by 9% before heat treatment. Automated interpretation increased sensitivity by 16.3% in unconcentrated samples. Before heat treatment, specificity remained high with visual interpretation (100% unconcentrated) but slightly decreased with automated reading (98% unconcentrated). After heat treatment, specificity reached 100% for all methods. In LPS-spiked samples, automated interpretation improved analytical sensitivity by 2- to 10-fold, particularly for mAb 3/1-positive strains.
Conclusion:
Both urine concentration and automated interpretation with the Digival™ reader increased the sensitivity of the BinaxNOW® assay. Automated interpretation achieved this without the additional processing step required for concentration and may therefore represent a practical alternative. Heat treatment of positive samples remains necessary to maintain optimal specificity.
