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Case report
Why does activated partial thromboplastin time prolongation occur in severe fever with thrombocytopenia syndrome?
  1. Atsushi Mizoe1,
  2. Junya Sakaue2 and
  3. Noriko Takahara1
  1. 1Department of Internal Medicine, Ako City Hospital, Ako, Hyogo, Japan
  2. 2Integrated Clinical Education Center, Kyoto University Hospital, Kyoto, Japan
  1. Correspondence to Dr Atsushi Mizoe; mizoe14ihsu{at}


Severe fever with thrombocytopenia syndrome (SFTS) is caused by infection with SFTS virus and this mortality rate is 16.2% to 30%. An 85-year-old male patient presented to the emergency department of the hospital with primary complaints of fever and consciousness disturbance. Haemophagocytic syndrome and prolonged activated partial thromboplastin time (APTT) without associated prolonged prothrombin time were observed, suggesting SFTS, which was eventually diagnosed. APTT-only prolongation has been reported previously with SFTS, but the mechanism is unknown. The absence of coagulation factors was determined by a cross-mixing study. In addition, examination of intrinsic coagulation factors showed reduced factor XI activity. These results suggest that factor XI is causally related to APTT-only prolongation in SFTS.

  • infectious diseases
  • haematology (incl blood transfusion)

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  • Contributors AM, JS and NT contributed to the diagnosis and implementation of the research, to the analysis of the results and to the writing of the manuscript.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests None declared.

  • Patient consent for publication Obtained.

  • Provenance and peer review Not commissioned; externally peer reviewed.