CF appears to be a risk factor for developing blood clots in the deep veins that can obstruct blood flow. In medical terms, we call this "venous thrombosis". It appears that most of the clots that have occurred in patients with CF are associated with having an intravenous (IV) catheter.  An IV is the line inserted in a vein to allow medications to be given.  If you have an IV and experience a swollen arm, or pain and tenderness around the IV, this may be a sign that there is a clot. It is important to tell your doctor so they can look at it and decide if an ultrasound needs to be done to look for a clot. We worry about blood clots because sometimes they can move from the deep veins into the blood vessels that connect the heart and the lungs and put pressure on the heart and the lungs. This can be life-threatening. There is little information on this topic in people with CF so at our centre we are evaluating it further.