Transactions of the Royal Society of Tropical Medicine and Hygiene · 2026
Acquired haemophilia B in Kyasanur Forest disease: a case series of isolated prolonged activated partial thromboplastin time.
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Gupta Nitin, Belurkar Sushma, Varma Muralidhar, Sebastian Anjely, Mukhopadhyay Chiranjay, Kumar Tirlangi Praveen
Аннотация
BACKGROUND: Kyasanur Forest disease (KFD) is a tick-borne viral haemorrhagic fever in which thrombocytopaenia and transaminitis are well recognized, but the basis of coagulation abnormalities remains incompletely understood. Isolated prolongation of the activated partial thromboplastin time (APTT) with a normal prothrombin time (PT) has been frequently observed, although the mechanism remains unclear.
CASE SERIES: We describe nine patients with confirmed KFD who had isolated prolonged APTT with normal PT during the acute phase of illness. The patients ranged in age from 29 to 78 years, and seven were female. The duration of fever before admission ranged from 3 to 8 days. One patient had epistaxis, while the remaining patients had no clinically evident bleeding manifestations. APTT ranged from 37.0 to 74.8 s. In all patients, mixing studies showed correction with aged serum but not with adsorbed plasma, suggesting isolated factor IX deficiency. Factor assays confirmed reduced factor IX activity, ranging from 24.0% to 48.4%, with preserved or elevated factor VIII levels. Factor IX inhibitor screening was negative in the two patients tested. On follow-up, APTT normalized in all patients. Repeat factor IX activity was available in eight patients and had returned to within the reference range in seven.
CONCLUSIONS: This case series suggests that transient acquired factor IX deficiency is an important explanation for isolated APTT prolongation in acute KFD. Recognition of this pattern may help distinguish selective intrinsic pathway dysfunction from disseminated intravascular coagulation and may guide appropriate coagulation support in severe disease.
CASE SERIES: We describe nine patients with confirmed KFD who had isolated prolonged APTT with normal PT during the acute phase of illness. The patients ranged in age from 29 to 78 years, and seven were female. The duration of fever before admission ranged from 3 to 8 days. One patient had epistaxis, while the remaining patients had no clinically evident bleeding manifestations. APTT ranged from 37.0 to 74.8 s. In all patients, mixing studies showed correction with aged serum but not with adsorbed plasma, suggesting isolated factor IX deficiency. Factor assays confirmed reduced factor IX activity, ranging from 24.0% to 48.4%, with preserved or elevated factor VIII levels. Factor IX inhibitor screening was negative in the two patients tested. On follow-up, APTT normalized in all patients. Repeat factor IX activity was available in eight patients and had returned to within the reference range in seven.
CONCLUSIONS: This case series suggests that transient acquired factor IX deficiency is an important explanation for isolated APTT prolongation in acute KFD. Recognition of this pattern may help distinguish selective intrinsic pathway dysfunction from disseminated intravascular coagulation and may guide appropriate coagulation support in severe disease.