The diagnosis of anemia indicates that the patient is experiencing a reduction in

Normally, RBCs survive in the circulation for 120 days. If the erythrocytic life span is shortened significantly (< 40 d), the patient has a hemolytic disorder that may be demonstrated by showing increased production of erythrocytes, increased destruction, or both. The former is revealed most readily by the presence of sustained reticulocytosis and the latter by the occurrence of indirect bilirubinemia (see Table 4, below). Other laboratory tests are available to detect hemolysis, but they are either more expensive or less reliable.

Table 4. Classification of the Hemolytic Disorders (Open Table in a new window)

Anemia solely due to hemolysis does not occur until RBCs are being destroyed at 6-8 times the normal rate, reducing the mean RBC life span to less than 20 days because of the bone marrow's capacity to undergo 6-fold hypertrophy and hyperplasia. Thus, if the clinician relies on the presence of anemia to detect hemolytic states, the clinician misses most of them and, perhaps, an important clue to an underlying disorder. On the other hand, if reticulocytosis and indirect bilirubinemia are used to detect hemolytic states, they are usually found when the mean life span is less than 40-50 days. More sophisticated methods, such as measurements of RBC lifespan, are required to detect less severe shortening of erythrocyte life span (50-100 d) and are only occasionally needed in clinical practice.

All patients with reticulocytosis and indirect bilirubinemia have a hemolytic disorder. All patients with sustained reticulocytosis have a hemolytic disorder. Unfortunately, the contrary is not the case, and significant hemolysis can occur without reticulocytosis if the bone marrow is unable to produce cells at an accelerated rate (eg, pernicious anemia, leukemia, aplasia).

A single demonstration of an elevated reticulocyte count is insufficient to establish a diagnosis of hemolysis, because transient reticulocytosis may occur without hemolysis (eg, in the treatment of iron deficiency anemia).

Almost all patients with indirect bilirubinemia have a hemolytic disorder. In adults, the exception is patients with Gilbert disease. These patients can be distinguished from those with hemolytic disorders and those who have no other obvious stigmata of hemolysis (eg, anemia, reticulocytosis, Coombs test) by having the patient fast for 3 days. In Gilbert disease, indirect bilirubin doubles with starvation, whereas in hemolytic disorders, it does not. Once the presence of hemolysis has been established, the etiology of the increased rate of RBC destruction can be sought.

All causes of hemolytic disorders are either hereditary or acquired. Similarly, they are due to either an intrinsic abnormality of the RBC (intracorpuscular defect) or external factors that shorten the erythrocyte life span (extracorpuscular). Using this nomenclature, only 4 groups of hemolytic disorders are possible—hereditary intracorpuscular, hereditary extracorpuscular, acquired intracorpuscular, and acquired extracorpuscular.

Hereditary hemolytic disorders

All hereditary hemolytic disorders are due to intracorpuscular defects, and most acquired disorders are due to extracorpuscular abnormalities (see Table 4). Hereditary etiologies of hemolytic disease are suggested strongly in any patient with a family history of anemia, jaundice, cholelithiasis, or splenectomy. Whenever possible, family members, particularly parents, siblings, and children, should undergo a hematologic examination, including a hemogram with reticulocyte count, an indirect bilirubin determination, and a careful examination of the peripheral smear.

If a specific hereditary hemolytic disorder (eg, hereditary spherocytosis, hemoglobinopathy) is suggested in a patient, examine blood from family members for that entity by appropriate laboratory methods. Establishment of a hemolytic defect in other closely related family members permits a presumptive diagnosis of hereditary intracorpuscular hemolytic disorder in the patient. Showing a similar RBC abnormality (eg, spherocytes, abnormal Hb, G-6-PD deficiency) among family members establishes the basic etiology. Once the probability of a hereditary hemolytic disorder is established, a planned approach to determine the definitive abnormality is usually simple.

A careful examination of the peripheral smear may reveal spherocytes in hereditary spherocytosis, ovalocytes in hereditary elliptocytosis, sickle cells in patients with major hemoglobinopathies associated with sickle Hb, target cells in patients with Hb C or E disease, and marked poikilocytosis with target cells, microcytes, and hypochromic RBCs in thalassemia. (See the images below.)

Even in certain rare disorders, abnormal erythrocyte morphology may provide an important clue. Examples are acanthocytosis in abetalipoproteinemia, stomatocytosis in the hereditary disorder of this name, and numerous target cells in lecithin cholesterol acyltransferase deficiency. Other laboratory studies of value in the hereditary hemolytic disorders include the following: [16]

• Hereditary spherocytosis - MCHC greater than 36%, incubated osmotic fragility in oxalate, and detection of the underlying molecular defect

• Hemoglobinopathies - Sickle cell preparation, Hb electrophoresis at 1 or more pH, heat denaturation test for unstable Hbs, oxygen disassociation for Hbs with abnormal oxygen affinity

• Thalassemia - A2 and fetal Hb, Hb electrophoresis, characterization of the molecular defect, quantification of alpha and beta chains

• Congenital dyserythropoietic anemias - Demonstration of abnormalities of erythroid precursors in bone marrow aspirates, positive acid hemolysis (Ham) test, with normal result of sucrose hemolysis test in one form of this disease (hereditary erythroblastic multinuclearity with a positive acidified serum test [HEMPAS])

• Hereditary RBC enzymatic deficiencies - Specific RBC enzyme assay

In clinical practice, approximately 90% of hereditary RBC enzymatic deficiencies with significant clinical manifestations are either G-6-PD deficiencies or abnormalities of pyruvic kinase. The age at which a hemolytic disorder is detected is not always helpful in determining whether the disorder is hereditary. Although the abnormality is inherited, congenital manifestations may be unusual. An infant with sickle cell anemia or beta thalassemia appears healthy at birth. Clinical manifestations usually do not occur in infants younger than 6 months, because fetal Hb has not been replaced by adult Hb until that age.

Usually, thalassemia minor is not detected until a routine hemogram is performed, and, then, it is often mistaken for iron deficiency anemia because of the microcytosis and hypochromia. Thus, the physician dealing with adult patients must be as aware of these disorders as the pediatrician.

The most commonplace of the hereditary disorders is G-6-PD deficiency, because it occurs in 10% of the African American population living in the United States. In this population, G-6-PD deficiency usually remains undetected until oxidant drugs are administered. Then, it produces a mild to moderate hemolytic anemia that is transient in nature. In white populations of Mediterranean derivation, G-6-PD deficiency can produce a chronic hemolytic anemia without exposure to drugs. Exposure to oxidant drugs can produce lethal hemolysis.

Acquired hemolytic disorders

Acquired hemolytic disorders occur in a large number of disease states and can vary considerably in severity. In addition, hemolysis may be observed as a result of physical injury to the RBC or following exposure to drugs, chemicals, or venoms. In many patients, the etiology of the hemolytic disorder is apparent because of other manifestations of the disease (eg, infections, collagen vascular disease).

A confirmed positive Coombs test result can be extremely helpful in this group of disorders. It provides assurance that the hemolytic disorder is an acquired extracorpuscular defect and limits it to the group of disorders associated with autoimmune hemolytic anemia; these disorders include the following:

• Drug-dependent antibodies (eg, to penicillin, quinidine, alpha methyldopa)

• Coexistence of an underlying disease (eg, hematologic malignancies, lupus erythematosus, certain viral infections)

• Idiopathic groups in which an underlying disease cannot be demonstrated

Usually, the acquired hemolytic disorders with intracorpuscular defects are not difficult to diagnose. Vitamin B12 and folic acid deficiencies are associated with macrocytic anemia, the presence of hypersegmented polymorphonuclear leukocytes in the peripheral smear, megaloblastic bone marrow, physical findings of the underlying cause of the deficiency state, and abnormal serum levels for the deficient vitamin.

Iron deficiency in the United States is rarely of sufficient severity to cause significant hemolysis and is merely mentioned herein for the sake of completeness.

Paroxysmal nocturnal hemoglobinuria is diagnosed only if the physician considers it in the differential diagnosis, and it may manifest by either a pancytopenia or a hemoglobinuria. However, flow cytometry to detect the absence or reduced expression of CD59 and CD55 on the patient's RBCs can help to exclude this cause of hemolysis.

Additional considerations

The major diagnostic problems encountered with hemolytic disorders are when the known causes for hemolysis have been excluded by history, physical examination, and laboratory studies; the Coombs test result is negative; and not enough family members can be tested to differentiate between hereditary intracorpuscular hemolytic disorders and acquired extracorpuscular defects.

A donor cell chromium survival study can be helpful in differentiating between a hereditary hemolytic disorder and an acquired hemolytic disorder. Labeled RBCs from a healthy blood donor in a compatible blood group allow for a normal survival rate in patients with hereditary hemolytic disease and a shortened life span in those with an acquired extracorpuscular defect.