Severe fever with thrombocytopenia syndrome (SFTS) is an emerging viral disease in East Asia with high mortality. Few studies have examined markers that suggest SFTS in febrile patients. To determine useful biochemical markers for SFTS, patients aged 18 years or older with SFTS or microbiologically confirmed community-onset bacteremia with thrombocytopenia (BT) at presentation between June 2013 and December 2015 were included from two tertiary university hospitals in Republic of Korea retrospectively. Eleven patients with SFTS and 62 patients with bacteremia and thrombocytopenia were identified in the study period. Age and sex did not show significant difference among two groups. Fever was more commonly observed but comorbidities were less common in SFTS than in BT (P < 0.05, each). The areas under the curves of serum ferritin, C-reactive protein, white blood cell count, serum procalcitonin, and fibrinogen were above 0.9, indicating the discriminative power of these biomarkers (1.000, 0.991, 0.963, 0.931, and 0.934, resp., all P < 0.05). The optimal cutoff value of serum ferritin was 3,822 ng/mL in this study. These results suggest that hyperferritinemia is a typical laboratory feature of SFTS, and the serum ferritin level can be used as a marker for clinicians suspecting SFTS.