Background: Congenital or acquired prothrombin deficiency is a rare condition.
Case Report: A 2-year-7-month old Thai girl presented with ecchymosis, bleeding at both thighs and right ear lobe after a
self-limited viral infection.

Results: The investigations revealed prolonged APTT and PT, prothrombin level 6% and positive anticardiolipin antibody
26.2 IU/mL. The 1:1 mixture of her plasma and normal plasma could not normalize her APTT and PT. The inhibitor to
prothrombin determined by Bethesda method was 0.62 BU. She was responsive to 20 ml/kg of FFP transfusion, followed by
10 ml/kg at an interval of 12 h for three days and daily 500 units of prothrombin complex concentrate administration for three
days. At two-week follow-up, she had no bleeding symptom, coagulation tests were normal, prothrombin level was normalized
at 94%, no inhibitor to prothrombin was detected, and anticardiolipin antibody became negative. The additional DNA
analysis of her prothrombin gene revealed nine different polymorphisms for which seven had been found in patients with
congenital prothrombin deficiency and two were novel (4096T→C, 4097T→C). These single nucleotide polymorphisms are
not the disease-causing mutations. In addition, neither known mutations inducing congenital prothrombin deficiency were
identified.

Conclusion: The acquired hypoprothrombinemia was concluded as the cause of bleeding in this reported patient. It might be
caused by the transient low titer of antiphospholipid antibody, which was responsive to replacement therapy of FFP and
prothrombin complex concentrate.

Keywords: Hypoprothrombinemia, Antiphospholipid antibody, Bleeding tendency, Prothrombin deficiency