Definition of Paroxysmal cold hemoglobinuria (PCH):

Paroxysmal cold hemoglobinuria (PCH) is a rare blood disorder in which the body's immune system produced antibodies that destroy red blood cells when they go from cold to warm temperatures.

Causes, incidence, and risk factors:

Paroxysmal cold hemoglobinuria only occurs in the cold, and affects mainly the hands and feet. Antibodies attach (bind) to red blood cells and to proteins in the blood (called complements). These antibodies destroy the red blood cells as they they move through the body and get rewarmed. As the cells are destroyed, hemoglobin, the part of red blood cells that carries oxygen, is released into the blood and passed in the urine.

PCH has been linked to secondary syphilis, tertiary syphilis, and other viral or bacterial infections. Sometimes the cause is unknown.

The disorder is rare.