A lot more is known about PNH since it was first named in the late 1800s. Health care providers now know that: The breaking apart of blood cells, called hemolysis, is always happening at some level in people with PNH. Signs and symptoms of PNH can happen at any time of day or night. While most people will experience dark-colored urine at some point, only 1 in 4 will experience it at diagnosis.