what are the causes of high blood urea?
['Urinary tract obstruction.', 'Congestive heart failure or recent heart attack.', 'Gastrointestinal bleeding.', 'Dehydration, resulting from not drinking enough fluids or for other reasons.', 'Shock.', 'Severe burns.', 'Certain medications, such as some antibiotics.', 'A high-protein diet.']