Systemic capillary leak syndrome (SCLS) causes fluid and proteins to leak out of tiny blood vessels (capillaries) into surrounding tissues. This may lead to very low blood pressure (hypotension), hypoalbuminemia, and thickened blood due to a decrease in plasma volume (hemoconcentration). Initial symptoms may include tiredness, nausea, abdominal pain, extreme thirst, and sudden increase in body weight. Complications can include general swelling, compartment syndrome, kidney failure, and stroke. SCLS occurs in episodes which vary in frequency, with some people having one episode in their lifetime, and others having several per year. The severity also varies, and the condition can be fatal. In many cases, the cause is not known (idiopathic SCLS). Diagnosis is based on the symptoms, clinical examination and other laboratory tests.