Among those are chronic kidney failure, chronic kidney disease without frank failure but with excessive protein loss, called nephrotic syndrome, congestive heart
disease, disease of a heart
valve, fat emboli (clots) in association
with long bone fractures, IV salt and/or water overload, high altitude, acute infection such as pneumonia with or without fever, and chronic infection with tuberculosis (TB) being a prime example. And, there are other less common causes.