Paroxysmal hemoglobinuria is usually defined as a syndrome or condition, presumably caused by a syphilitic infection and manifesting itself by recurring paroxysms of hemoglobinuria and by characteristic constitutional symptoms. The blood of patients who suffer from this condition is presumed to contain, in latent form, a specific hemolysin which becomes active when the blood is chilled and which produces the paroxysms. On account of the part played by cold, the condition has been given such names as kälthamoglobinurie, hemoglobinuria a frigore and chilling hemoglobinuria.
The condition may occur at any age, but it is rarely observed in patients more than 50 years of age. It is as common in children as in adults. The majority of the patients are male.
Strictly speaking, the condition should not be described as paroxysmal. The attacks or crises can always occur under well defined conditions or can be induced artificially by similar conditions.