Mrs. Foster is a 50-year-old female who comes to the ER complaining about some chest discomfort that seems worse when she takes a breath in and shortness of breath. She also feels like her heart is racing. Her past medical history is unremarkable except for mild hypertension. She usually takes an aspirin a day because she heard it was a good idea to take it, but she stopped taking it one week ago when she noticed some blood in her stool. She thinks her mother may have had a blood clot in her leg during one of her pregnancies. Mrs. Foster is married with no children. On physical examination in the emergency room, her HR is 110/min, RR 28/min, BP 122/70, oxygen saturation 86% on room air. Her chest and precordial exam are normal. Her left leg is normal in colour, slightly warm and edematous. The circumference of her left calf is 3 cm larger the circumference of her right calf. She complains of pain when you palpate behind her knee. Her pedal pulses are palpable. The ER staff person calculates her Wells Score and based on the result, orders a D-dimer blood test.