Well I don't know about "poisonous" per se, but in sickle cell anemia, when serious clotting crises occur, the victim must get infused with fresh blood and sometimes plasmaphoresis (filtering out tiny clots). This can also occur with other severe clotting disorders. But in total renal failure, the kidneys shut down and stop filtering wastes and excess electrolytes from the blood into urine for removal, then metabolic wastes (urea, uric acid, creatinine) and minerals build up, and must be dialyzed out by machines and filters. Uremia, urea waste build-up, and hyperkalemia (excessive blood potassium) can become so severe as to be life-threatening.
