ABSTRACT
Protein S deficiency is one of the several risk factors for thrombophilia and can cause blood clotting disorders such as deep vein thrombosis and pulmonary embolism. A 54-year-old man was admitted with the complaint of dyspnea and was diagnosed with pulmonary embolism. The patient had very low level of free protein S, total protein S antigen, and protein S activity (type I protein S deficiency). In history taking, we found that his mother, 78 year old, had a history of same disease 10 years ago, and confirmed the pronounced low level of protein S. The patient's son also had very low level of protein S, however there had not been any history of pulmonary embolism yet. This case study suggests that asymptomatic persons with a family history of protein S deficiency and pulmonary embolism should be checked regularly for early detection of the disease, as protein S deficiency can be suspected.