Hemolytic Anemia

1. Symptoms of anemia:

a. extraction of oxygen by the tissues can increase from a baseline of 25% to a maximum of about 60 % in the presence of anemia or hypoperfusion. Therefore, normal oxygen delivery can be maintained by enhanced extraction alone down to a hemoglobin concentration of 8 to 9 g/dL

b. with cardiac compensation (increases in stroke volume and heart rate), oxygen delivery can be maintained at rest at a hemoglobin concentration as low as 5 g/dL (Hct of 15), assuming that the intravascular volume is maintained

c. symptoms occur at rest when hemoglobin falls below 5, or higher during any exertion or in patients who have impaired cardiac compensation (symptoms include DOE, fatigue, bounding pulses, palpitations etc.) More severe anemia can lead to CHF, angina, arrhythmia, and/or MI.

2. Direct Coombs test:  AKA the “antiglobulin” test:

a. Step 1: RBCs of the patient are washed to remove adherent proteins

b. Step 2: The RBCs are then mixed with an antiserum or monoclonal antibodies prepared against the various immunoglobulins (ie IgG) and a fragment of the third component of complement, C3d.

c. Step 3: the reaction is noted and quantitated based on the agglutination of red cells after the antiserum is added

d. The antibody agglutination pattern (IgG vs. complement) can help determine the type of AIHA (warm vs. cold, etc.)

e. As a reminder, the indirect Coombs test is used by mixing patient and control serum to help determine blood transfusion compatibility and Rh factor determination.

3. Reticulocyte count

a. Normal reticulocyte percentage is 0.5 to 1.5%

b. Assuming the bone marrow is normal and there are sufficient erythropoeitin and iron stores, acute anemia (ie. hemolysis or blood loss) should increase the retic % to 4-6%

c. The absolute reticulocyte count (or reticulocyte index) is reflective of the underlying degree of anemia and must be corrected based on the hematocrit

d. The corrected reticulocyte count is equal to the patient's Hct divided by 45 and multiplied by the percentage of reticulocytes. RI= retic % x Hct/45

(In general, a reticulocyte index >2=appropriate BM compensation.

e. Remember that early reticulocytes are bigger than mature red cells, so a high reticulocyte count elevates the MCV.

4. Hemolytic anemia

a. Intrinsic vs. Extrinsic:

 i. Intrinsic causes:  With few exceptions (ie. PNH), the causes of intrinsic RBC defects are hereditary, they involve components of the RBC (hemoglobin, cell membrane, metabolic enzymes).

· hereditary spherocytosis

· thalassemia

·Paroxysmal Nocturnal Hemoglobinuria

· G6PD-deficiency

ii. Extrinsic causes:  Extracorpuscular (extrinsic) causes are almost always acquired conditions leading to increased destruction of otherwise normal RBCs.

· Ab-mediated (AIHA, drug-induced, delayed transfusion rxn)

· Hypersplenism (also involved in AIHA and intrinsic causes)

· Trauma (valves, fibrin strands in DIC, TTP)

· Exposure to oxidizing compounds (dapsone, pyridium etc.) in pts with G6PD-deficiency or in otherwise normal pts

· Infectious pathogens (ie. malaria, clostridia, babesiosis)

· Snake or insect bites

iii. Site of destruction (intravascular or extravascular hemolysis):

· The severity and type of red cell alteration determine the cell's site of destruction. In most cases (ie. oxidant attack, metabolic insult, hemoglobinopathy) the insult leads to an alteration of the RBC membrane

· If the damage is severe enough, immediate lysis occurs within the circulation (intravascular hemolysis)

· If the damage is less severe, the cell is destroyed within the monocyte-macrophage system in the spleen, liver, bone marrow, and lymph nodes (extravascular hemolysis)

iv. Autoimmune Hemolytic Anemia (AIHA)

Warm AB AIHA:

1. Often idiopathic, but can be due to: viral infections (mycoplasma and infectious mono), autoimmune diseases (SLE), malignancies of immune system (CLL etc), prior HSCT, drugs (cephalosporins, PCN, NSAIDs, quinine derivatives)

2. Presence of spherocytes on smear (due to RBC membrane deformity)

3. + direct coombs for IgG +/- C3

4. Can be associated with venous thromboembolism

5. Treatment: Initial treatment with corticosteroids, if poorly responsive or resistant disease, consider elective splenectomy.  For patients unwilling or unable to undergo splenectomy, or for those who have failed or relapsed following splenectomy, consider other immunosuppressive or cytotoxic agents (ie. rituximab, azathioprine, cyclophosphamide, cyclosporine). There is insufficienct information from RCTs to choose one of these agents over another.

Cold AB AIHA:

6. IgM, agglutination at cold temperatures (acrocyanosis)

7. Anti C3-d on direct coombs

8. Often associated with malignancy (CLL, lymphoma, etc) or infection (mycoplasma, mononucleosis)

9. Treatment is usually directed at the underlying cause (ie. infection) and avoidance of cold triggers

** you should only see hemoglobinuria with intravascular hemolysis (usually due to complement mediated destruction of RBCs, which can occur in pts with warm ab AIHA, but more common in cold ab AIHA).  However, you do see unconjugated hyperbilirubinemia in any type of hemolysis (since the biliverdin still has to be metabolized).  Similarly the urine can be dark from urobilinogins. 

See quote from William’s Hematology, 8th edition, Ch. 53

“Hyperbilirubinemia (chiefly unconjugated) is highly suggestive of hemolytic anemia, although its absence does not exclude the diagnosis. Total bilirubin is only modestly increased (up to 5 mg/dL) and, with rare exceptions, the conjugated (direct) fraction constitutes less than 15 percent of the total. Urinary urobilinogen is increased regularly, but bile is not detected in the urine unless serum conjugated bilirubin is increased. Usually, serum haptoglobin levels are low, and lactate dehydrogenase levels are elevated. Hemoglobinuria is encountered in rare patients with warm-antibody AHA and hyperacute hemolysis, more commonly in patients with cold agglutinin disease, and characteristically in patients with paroxysmal cold hemoglobinuria and with drug-immune hemolytic anemia mediated by the ternary complex mechanism.” 

(Victoria Kelly MD, 2/18/11)