What is the difference between intravascular and extravascular hemolysis

Red blood cells RBCs have a normal life span of approximately days. An operational definition of hemolysis, therefore, is accelerated RBC destruction with premature removal from the circulation, which usually causes anemia. Hemolytic anemia can occur in a wide range of clinical settings featuring various etiologies; signs and symptoms reflect the location and severity of hemolysis.

Intravascular hemolysis occurs when erythrocytes are destroyed in the blood vessel itself, whereas extravascular hemolysis occurs in the hepatic and splenic macrophages within the reticuloendothelial system.

Intravascular hemolysis is often dramatic, with free hemoglobin released into the plasma leading to hemoglobinuria positive blood on urine dipstick but few erythrocytes on microscopic examination. Examples of intravascular hemolysis include enzyme defects such as glucosephosphate dehydrogenase G6PD deficiency or certain immune-mediated processes. Extravascular hemolysis usually results from more subtle RBC destruction, typically with chronic splenic enlargement and jaundice.

Extravascular hemolysis is more common with RBC membrane disorders such as hereditary spherocytosis. Some forms of hemolytic anemia feature both intravascular and extravascular hemolysis. The degree of anemia depends on how rapidly the erythrocytes are being removed from circulation and how well the bone marrow compensates with increased reticulocytosis.

The clinical presentation of hemolytic anemia is highly variable, ranging from mild anemia with asymptomatic splenomegaly, to jaundice with splenomegaly and dark urine, to acute severe anemia as a consequence of a parvovirus-induced aplastic crisis.

On physical examination, patients may have a cardiac flow murmur, splenomegaly, and scleral icterus. Some children have a relatively benign physical examination and medical history. The classic laboratory finding of hemolysis is anemia with an elevated reticulocyte count. The reticulocytosis reflects normal bone marrow function and occurs in response to the premature RBC destruction; reticulocytes are larger than older erythrocytes and have a blue-purple color known as polychromasia Fig. Reticulocytosis generally occurs 3 to 5 days after a sudden drop in hemoglobin concentration but is relatively constant in children with congenital hemolytic anemia.

Making the diagnosis of hemolytic anemia begins with recognizing the constellation of signs and symptoms, then obtaining a complete blood count with reticulocyte count, and finally examining the peripheral blood smear.

Additional laboratory findings supporting the diagnosis of hemolysis include elevated total serum bilirubin and lactate dehydrogenase LDH; LDH being released from RBCs during hemolysis.

Intravascular hemolysis also causes decreased or undetectable levels of haptoglobin, but this test is not specific so is not generally helpful. Dipstick urinalysis may reveal bilirubin, protein, or blood; the presence of blood without erythrocytes on microscopic analysis indicates hemoglobinuria reflecting intravascular hemolysis.

Compared to mature erythrocytes, reticulocytes just entering the circulation are larger and have a bluish-purple hue. The presence of reticulocytes indicates a bone marrow response to anemia and is often found in children with hemolytic anemia. The peripheral smear will show schistocytes or other fragmented red cells with mechanical hemolysis. Other suggestive findings include increased levels of serum LDH and indirect bilirubin with a normal ALT, and the presence of urinary urobilinogen.

Intravascular hemolysis is suggested by RBC fragments schistocytes on the peripheral smear and by decreased serum haptoglobin levels; however, haptoglobin levels can decrease because of hepatocellular dysfunction and can increase because of systemic inflammation.

Intravascular hemolysis is also suggested by urinary hemosiderin. Urinary hemoglobin, like hematuria and myoglobinuria, produces a positive benzidine reaction on dipstick testing; it can be differentiated from hematuria by the absence of RBCs on microscopic urine examination.

Free hemoglobin may make plasma reddish brown, noticeable often in centrifuged blood; myoglobin does not. Once hemolysis has been identified, the etiology is sought. To narrow the differential diagnosis in hemolytic anemias.

Most hemolytic anemias cause abnormalities in one of these variables, and so test results can direct further testing. A positive result suggests the presence of autoantibodies to RBCs if the patient has not received a transfusion in the last 3 mo, alloantibodies to transfused RBCs usually seen in acute or delayed hemolytic reaction , or drug-dependent or drug-induced antibodies against RBCs. This test is also used to determine the specificity of an alloantibody.

Although some tests can help differentiate intravascular from extravascular hemolysis, making the distinction is sometimes difficult. During increased RBC destruction, both types are commonly involved, although to differing degrees. Corticosteroids are helpful in the initial treatment of warm antibody autoimmune hemolysis. Splenectomy is beneficial in some situations, particularly when splenic sequestration is the major cause of RBC destruction.

If possible, splenectomy is delayed until 2 weeks after vaccination with the following:. Vaccines are directed against many of Haemophilus influenzae vaccine Haemophilus influenzae Type b Hib Vaccine Haemophilus influenzae type b Hib vaccines help prevent Haemophilus infections but not infections caused by other strains of H.

Meningococcal vaccine Meningococcal Vaccine The meningococcal serogroups that most often cause meningococcal disease in the US are serogroups B, C, and Y. Serogroups A and W cause disease outside the US. Current vaccines are directed In cold agglutinin disease, avoidance of cold is recommended, and blood will need to be warmed before transfusion.

Folate replacement is needed for patients with ongoing long-term hemolysis. From developing new therapies that treat and prevent disease to helping people in need, we are committed to improving health and well-being around the world. The Manual was first published in as a service to the community. Learn more about our commitment to Global Medical Knowledge. This site complies with the HONcode standard for trustworthy health information: verify here.

Common Health Topics. Videos Figures Images Quizzes Symptoms. Disorders extrinsic to the red blood cell Intrinsic red blood cell abnormalities. Normal red blood cell processing Extravascular hemolysis Intravascular hemolysis Consequences of hemolysis. Symptoms and Signs. Anemias Caused by Hemolysis. Test your knowledge. Liberated hemoglobin is converted into unconjugated bilirubin in the spleen or may be bound in the plasma by haptoglobin.

The hemoglobin-haptoglobin complex is cleared quickly by the liver, leading to low or undetectable haptoglobin levels. Algorithm for the evaluation of hemolytic anemia.

Treatment of underlying disorder; removal of offending drug; steroids, splenectomy, IV gamma globulin, plasmapheresis, cytotoxic agents, or danazol Danocrine ; avoidance of cold. Cultures, thick and thin blood smears, serologies. Spherocytes, family history, negative DAT.

Hemoglobin electrophoresis, genetic studies. In cases of severe intravascular hemolysis, the binding capacity of haptoglobin is exceeded rapidly, and free hemoglobin is filtered by the glomeruli.

The renal tubule cells may absorb the hemoglobin and store the iron as hemosiderin; hemosiderinuria is detected by Prussian blue staining of sloughed tubular cells in the urinary sediment approximately one week after the onset of hemolysis.

Once the diagnosis of hemolysis is made on the basis of laboratory and peripheral smear findings Figure 1 , it is necessary to determine the etiology. While most forms of hemolysis are classified as predominantly intravascular or extravascular, the age of onset, accompanying clinical presentation, and co-existing medical problems usually guide the clinician to consider either an acquired or a hereditary cause 5 , 6 Table 1. Immune hemolytic anemias are mediated by antibodies directed against antigens on the red blood cell surface.

Microspherocytes on a peripheral smear and a positive direct antiglobulin test are the characteristic findings. Immune hemolytic anemia is classified as autoimmune, alloimmune, or drug-induced, based on the antigen that stimulates antibody- or complement-mediated destruction of red blood cells. Autoimmune hemolytic anemia AIHA is mediated by autoantibodies and further subdivided according to their maximal binding temperature.

When warm autoantibodies attach to red blood cell surface antigens, these IgG-coated red blood cells are partially ingested by the macrophages of the spleen, leaving microspherocytes, the characteristic cells of AIHA Figure 2. Cold autoantibodies IgM temporarily bind to the red blood cell membrane, activate complement, and deposit complement factor C3 on the cell surface. These C3-coated red blood cells are cleared slowly by the macrophages of the liver extravascular hemolysis.

The direct antiglobulin test DAT , also known as the direct Coombs' test, demonstrates the presence of antibodies or complement on the surface of red blood cells and is the hallmark of autoimmune hemolysis. Agglutination of the patient's antibody- or complement-coated red blood cells by anti-IgG or anti-C3 serum constitutes a positive test Figure 3.

Although most cases of autoimmune hemolysis are idiopathic, potential causes should always be sought. Lymphoproliferative disorders e. A number of commonly prescribed drugs can induce production of both types of antibodies Table 2. Human immunodeficiency virus infection can induce both warm and cold AIHA. The rightsholder did not grant rights to reproduce this item in electronic media. For the missing item, see the original print version of this publication.

AIHA should be managed in conjunction with a hematologist. Corticosteroids and treatment of any underlying disorder are the mainstay of therapy for patients with warm AIHA. Refractory cases may require splenectomy, intravenous gamma globulin, plasmapheresis, cytotoxic agents, or danazol Danocrine. All of the aforementioned therapies are generally ineffective for cold AIHA, which is managed most effectively by avoidance of the cold and treatment of any underlying disorder. Direct antiglobulin test, demonstrating the presence of autoanti-bodies shown here or complement on the surface of the red blood cell.

DAT Site of hemolysis Medications. Autoimmune hemolytic anemias. Hematology: basic principles and practice. Philadelphia: Churchill Livingstone, Drug-induced immune hemolysis is classified according to three mechanisms of action: drug-absorption hapten-induced , immune complex, or autoantibody. Hemolysis resulting from high-dose penicillin therapy is an example of the drug-absorption mechanism, in which a medication attached to the red blood membrane stimulates IgG antibody production.

When large amounts of drug coat the cell surface, the antibody binds the cell membrane and causes extravascular hemolysis. Quinine-induced hemolysis is the prototype of the immune complex mechanism, in which the drug induces IgM antibody production.

The drug-antibody complex binds to the red blood cell membrane and initiates complement activation, resulting in intravascular hemolysis. Alpha-methyldopa is the classic example of antierythrocyte antibody induction.

Although the exact mechanism is unknown, the drug perhaps by altering a red blood cell membrane protein and rendering it antigenic 13 induces the production of antierythrocyte IgG antibodies and causes an extravascular hemolysis.

The most severe alloimmune hemolysis is an acute transfusion reaction caused by ABO-incompatible red blood cells. For example, transfusion of A red cells into an O recipient who has circulating anti-A IgM antibodies leads to complement fixation and a brisk intravascular hemolysis. Within minutes, the patient may develop fever, chills, dyspnea, hypotension, and shock.

Delayed hemolytic transfusion reactions occur three to 10 days after a transfusion and usually are caused by low titer antibodies to minor red blood cell antigens. On exposure to antigenic blood cells, these antibodies are generated rapidly and cause an extravascular hemolysis. Compared with the acute transfusion reaction, the onset and progression are more gradual.

Microangiopathic hemolytic anemia MAHA , or fragmentation hemolysis, is caused by a mechanical disruption of the red blood cell membrane in circulation, leading to intravascular hemolysis and the appearance of schistocytes, the defining peripheral smear finding of MAHA Figure 4. When red blood cells traverse an injured vascular endothelium—with associated fibrin deposition and platelet aggregation—they are damaged and shredded.

This fragmentation occurs in a diverse group of disorders, including thrombotic thrombocytopenic purpura, hemolytic uremic syndrome, disseminated intravascular coagulation, preeclampsia, eclampsia, malignant hypertension, and scleroderma renal crisis. In addition, intravascular devices, such as prosthetic cardiac valves and transjugular intrahepatic portosystemic shunts, can induce MAHA.

Numerous mechanisms link infection and hemolysis. In addition, certain infectious agents are directly toxic to red blood cells. Malaria is the classic example of direct red blood cell parasitization.

Plasmodium species, introduced by the Anopheles mosquito, invade red blood cells and initiate a cycle of cell lysis and further parasitization. Both the cellular invasion and the metabolic activity of the parasite alter the cell membrane, leading to splenic sequestration. The diagnosis is made by the observation of intracellular asexual forms of the parasite on thick and thin blood smears. Similarly, Babesia microti and Babesia divergens , tick-borne protozoa, and Bartonella bacilliformis , a gram-negative bacillus transmitted by the sandfly, cause extravascular hemolysis by direct red blood cell invasion and membrane alteration.

Septicemia caused by Clostridium perfringens , which occurs in intra-abdominal infections and septic abortions, causes hemolysis when the bacterium releases alpha toxin, a phospholipase that degrades the red blood cell membrane.

The mature red blood cell, while biochemically complex, is a relatively simple cell that has extruded its nucleus, organelles, and protein-synthesizing machinery. Defects in any of the remaining components—enzymes, membrane, and hemoglobin—can lead to hemolysis.

The most common enzymopathy causing hemolysis is G6PD deficiency. G6PD is a critical enzyme in the production of glutathione, which defends red cell proteins particularly hemoglobin against oxidative damage. This X-linked disorder predominantly affects men. More than G6PD variants exist worldwide, but only a minority cause hemolysis.

Most patients have no clinical or laboratory evidence of ongoing hemolysis until an event—infection, drug reaction Table 3 , 19 or ingestion of fava beans—causes oxidative damage to hemoglobin. The oxidized and denatured hemoglobin cross-links and precipitates intracellularly, forming inclusions that are identified as Heinz bodies on the supravital stain of the peripheral smear. The altered erythrocytes undergo both intravascular and extravascular destruction.

Older red blood cells are most susceptible, because they have an intrinsic G6PD deficiency coupled with the normal age-related decline in G6PD levels. Hemolysis occurs two to four days following exposure and varies from an asymptomatic decline in hemoglobin to a marked intravascular hemolysis. Even with ongoing exposure, the hemolysis usually is self-limited, as the older G6PD-deficient cells are destroyed.

There is no specific therapy other than treatment of the underlying infection and avoidance of implicated medications.

In cases of severe hemolysis, which can occur with the Mediterranean-variant enzyme, transfusion may be required. G6PD activity levels may be measured as normal during an acute episode, because only nonhemolyzed, younger cells are assayed.

If G6PD deficiency is suspected after a normal activity-level measurement, the assay should be repeated in two to three months, when cells of all ages are again present. Adapted with permission from Beutler E.

G6PD deficiency. Blood ;