Dengue often presents with non-specific clinical signs, and given the current paucity of accurate, rapid diagnostic laboratory tests, identifying easily obtainable bedside markers of
dengue remains a priority. Previous studies in febrile Asian children have suggested that the combination of a positive
tourniquet test (TT) and leucopenia can distinguish
dengue from other febrile illnesses, but little data exists on the usefulness of these tests in adults or in the Americas. We evaluated the diagnostic accuracy of the TT and leucopenia (white blood cell count <5000/mm(3)) in identifying
dengue as part of an acute febrile illness (AFI) surveillance study conducted in the Emergency Department of Saint Luke's Hospital in Ponce, Puerto Rico. From September to December 2009, 284 patients presenting to the ED with
fever for 2-7 days and no identified source were enrolled. Participants were tested for
influenza,
dengue,
leptospirosis and enteroviruses. Thirty-three (12%) patients were confirmed as having
dengue; 2 had
dengue co-infection with
influenza and
leptospirosis, respectively. An infectious etiology was determined for 141 others (136
influenza, 3 enterovirus, 2
urinary tract infections), and 110 patients had no infectious etiology identified. Fifty-two percent of laboratory-positive
dengue cases had a positive TT versus 18% of patients without
dengue (P<0.001), 87% of
dengue cases compared to 28% of non-
dengue cases had leucopenia (P<0.001). The presence of either a positive TT or leucopenia correctly identified 94% of
dengue patients. The specificity and positive predictive values of these tests was significantly higher in the subset of patients without pandemic
influenza A H1N1, suggesting improved discriminatory performance of these tests in the absence of concurrent
dengue and
influenza outbreaks. However, even during simultaneous AFI outbreaks, the absence of leucopenia combined with a negative
tourniquet test may be useful to rule out
dengue.