AST to ALT Ratio is elevated in disseminated histoplasmosis as compared to localized pulmonary disease and other endemic mycoses.

Severe pulmonary or disseminated histoplasmosis often necessitates presumptive antifungal treatment while awaiting definitive diagnosis. Histoplasma antigen assays have improved sensitivity but results may lag up to 7 days. In order to increase diagnostic certainty, "soft clues" may be looked for in laboratory and radiologic data, such as elevated alkaline phosphatase or ferritin levels and findings of mediastinal adenopathy or hepatosplenomegaly. To determine if elevated aspartate aminotransferase (AST) to alanine aminotransferase (ALT) ratio is specific to histoplasmosis or a non-specific marker for disseminated fungal infection or sepsis in general, we retrospectively examined records of all patients diagnosed with an endemic fungal infection (EFI) at Rush University Medical Center from January of 1997 to October of 2012, and a cohort of septic patients with elevated liver enzymes. We identified 90 cases of EFIs during the study period that met all inclusion criteria (Histoplasma 21, Blastomyces 56, Coccidioides 12, Paracoccidioides 1). We also evaluated 10 control patients with bacterial sepsis. The mean ratio of AST to ALT in patients with disseminated histoplasmosis was 2.69 (95% CI:1.22, 4.16) while for other EFIs, the mean ratio ranged from 0.38 to 1.14 with disseminated coccidioidomycosis and blastomycosis respectively (P < 0.0001). The ratio in patients with bacterial sepsis was 0.84. We propose the use of the AST/ALT ratio as a clinical "soft clue" suggestive of disseminated histoplasmosis in the appropriate host, and to possibly distinguish cross reactivity of the Histoplasma antigen assay with other EFIs.