The Utility of the ALT: AST ratio as an early screening test for dengue fever

Abstract

OBJECTIVES: Early diagnosis of dengue infection is important to reduce morbidity and mortality. The widely used antibody test becomes positive only after the fifth day of fever, and viral diagnosis by PCR is expensive and not widely available. Liver transaminases are commonly elevated in dengue, and the aspartate aminotransferase: alanine aminotransferase (AST: ALT) ratio is >1. This study was done to determine the utility of the AST/ALT ratio >1 as a test to detect dengue infection early. Methods: We recruited all patients aged 18 to 65 years who were not pregnant, with fever less than three days admitted to hospital from September 2009 to January 2010 during the current dengue epidemic. In addition to routine invetigations and management, all patients had liver transaminases (AST and ALT) measured on day 3, and dengue IgM antibody on day five of the illness. Statistical analysis was performed using SPSS 16. RESULTS: 117 patients [65 males; mean age 32 years (SD =14.7)] were recruited. 83/117 (70.9%) were confirmed as dengue infection. AST: ALT >1 was significantly more common in dengue compared to other short duration fevers (75/83 vs 13/34, pO.OOl; Chi squared test). AST: ALT ratio >1 on day 3 had a sensitivity of 90.4% and specificity of 61.8% to detect dengue. The positive predictive value and negative predictive value of the ratio were 85.2% and 72.4% respectively. CONCLUSIONS: AST/ALT ratio seems a useful test to differentiate dengue fever from other short duration febrile illnesses in an epidemic setting.