Two forms of cold antibody autoimmune hemolytic anemias are generally recognized: Donath-Landsteiner hemolytic anemia (DLHA) and cold agglutinin disease.
DLHA is an intravascular hemolytic anemia caused by a cold-reacting immunoglobulin (Ig). In the majority of patients, the antibody is directed specifically against the P or I antigen on the red blood cell (RBC) surface. Most cases are due to polyclonal IgG but IgM-induced DLHA has been described. [1, 2, 3]
In contrast to DLHA, cold agglutinin disease is always due to a cold-reacting IgM antibody. Cold agglutinin disease is described in a separate Medscape Reference article (see Cold Agglutinin Disease).
As early as 1865, it was known that exposure to cold may result in paroxysms of hemoglobinuria. Over the ensuing decades, the etiology of the condition was elucidated and a diagnostic test was developed.  In 1904, Donath and Landsteiner reported their characterization of the causative antibody. 
The discovery of the Donath-Landsteiner (D-L) antibody permits DLHA to be distinguished from other causes of hemoglobinuria,  and the presence of the D-L antibody is pathognomonic for the condition.
In most cases, DLHA is associated with a sudden onset of hemoglobinuria after exposure to cold temperature. It is important to note, however, that hemoglobinuria may be absent and is not required for diagnosis (see Workup). Furthermore, a history of cold exposure is not always obtained.
Treatment of DLHA depends on the severity of the signs and symptoms and the presence of an underlying cause. In children, the condition is usually transient and mild. In such cases, treatment consists of expectant management only. If the anemia is severe or rapidly progressive, however, supportive care with transfusions of packed red blood cells may be warranted. In select moderate or severe cases, medication administration is appropriate. (see Treatment).
Teach patients to observe for signs and symptoms of anemia (eg, dyspnea, palpitations, fatigue, pallor) and to observe for signs of hemolysis (eg, jaundice, dark urine, pain). Instruct patients to avoid exposure to extreme cold, if possible. The possibility of hemolysis with strenuous exercise should also be discussed.
The autoantibody responsible for Donath-Landsteiner hemolytic anemia (DLHA) is a cold-reacting immunoglobulin known as the D-L autoantibody. The D-L autoantibody is a biphasic hemolysin capable of causing severe hemolysis even when the titer detected is low. This is due to its ability to detach from lysed RBCs and subsequently bind intact erythrocytes with changes in temperature.
D-L antibodies are directed against antigens expressed on the RBC membrane. Most commonly, the target is the P antigen but I antigen specificity and others have been described. 
The antibody attaches to RBC surfaces in the peripheral circulation, where temperatures are cooler (< 30°C). After binding, the D-L autoantibody activates the complement cascade, resulting in perforation of the RBC membrane (ie, intravascular hemolysis). Complement activation and resulting hemolysis occur only after the RBC travels to an area of warmer temperature (37°C) in the central circulation.
Therefore, the direct antiglobulin test (DAT) results are positive with anti-C3 but negative with anti-IgG or anti-IgM, unless the test is begun at 4°C and subsequently incubated at 37°C (see Workup). 
The antibody typically appears days to weeks after the trigger and may persist for months.
Donath-Landsteiner hemolytic anemia (DLHA) may be either idiopathic or secondary to an identifiable cause. Historically, the secondary type is most closely associated with late-stage or chronic congenital syphilis. Acute cases are often deemed idiopathic but are generally presumed to be secondary to a preceding viral illness or to an immunization. A definitive causative agent is rarely identified.
Viral infections that have been associated with acute Donath-Landsteiner hemolytic anemia include the following:
Bacterial infections associated with acute DLHA include those caused by the following pathogens  :
Acute autoimmune hemolytic anemia (AIHA) is relatively rare. 
Acute Donath-Landsteiner hemolytic anemia (DLHA) is more common in children than in adults. In children, the D-L autoantibody is a common cause of AIHA.
In one review of 52 patients with D-L antibodies, the median age was 5 years (range, 1-82 y).  Due to under-diagnosis, the true incidence is unknown but DLHA may represent 30-40% of all pediatric AIHA cases cases. 
No racial or ethnic predilection has been noted.
Most patients with Donath-Landsteiner hemolytic anemia (DLHA) do not require intervention. In rare cases, a severe acute drop in hemoglobin may be life threatening. These children may develop hypovolemic shock and cardiac failure.
Another potential complication of DLHA is acute tubular necrosis due to hemoglobinuria.
In general, however, prognosis in DLHA is very good, with most patients recovering spontaneously within 1 month of disease onset. 
Mild chronic hemolytic anemia has been observed in several children with the possibility of recurrence on exposure to cold or with illness.
Chronic syphilis-associated DLHA resolves with appropriate treatment of the underlying disease.
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