Optimal cutoff value of serum adenosine deaminase activity for diagnosing acute scrub typhus.

The objective of this study was to determine the optimal cutoff value of serum adenosine deaminase (ADA) activity for diagnosing scrub typhus in acute febrile patients, especially in the autumn. A total of 715 febrile patients were included; 286 of them were diagnosed with acute scrub typhus. The mean serum ADA activities in patients with and without scrub typhus were 42.8 ± 13.4 IU/L and 17.2 ± 11.5 IU/L, respectively. The optimal cutoff value for serum ADA activity was determined to be 25.0 IU/L with a sensitivity of 92.3%, specificity of 86.6%, and area under the curve of 89.4% using a receiver-operating characteristic curve analysis. The possibility of scrub typhus must be considered when acute febrile patients present with high ADA activity (>25 IU/L), especially in the autumn. Determining the optimal serum ADA activity cutoff value may help clinicians diagnose acute scrub typhus prior to serological confirmation.