Paroxysmal cold hemoglobinuria is a condition where antibodies are formed against a specific blood group. These antibodies bind the red blood cells and a cell-lysing blood protein called complement only in the cold, and usually in the extremities (hands and feet).

When the blood cells are rewarmed in the body, they are lysed (broken down). Hemoglobin is released in the blood and passed in the urine as blood cells are broken down.

The disease has been associated with secondary syphilis, tertiary syphilis, and other infections (caused by viruses or bacteria). Sometimes the cause is unknown.

Recovery from the attacks occurs very quickly, and people with this disease do not experience symptoms between episodes. Usually, the attacks end as soon as the sensitized cells are gone from the circulation. The risk factors are viral infection and syphilis. The disorder is rare.