By Helene DiCaro, PA-C, BS, MT

In the United States each day, people receive lifesaving blood transfusions for medical and surgical conditions. According to the National Blood Data Resource Center (NBDRC), about 13.9 million units of whole blood were collected in the United States in 1999. The NBDRC also states that hospitals transfused 12.4 million units of whole blood and red blood cells (erythrocytes) to 4.5 million patients in the same year.

The American Association of Blood Banks (AABB) states that transfusions are indicated to maintain or restore blood volume, oxygen-carrying capacity, hemostasis or leukocyte function. Blood transfusions are required for cases of trauma, organ and bone marrow transplants and heart surgery, to name a few. Transfusion also is necessary for patients receiving treatment for cancer, leukemia, thalassemia, sickle cell disease or burns. A unit of whole blood can be processed into multiple components, such as RBCs, leukocytes, plasma, platelets and cryoprecipitate. It also can be separated into plasma derivatives such as albumin, fibrinogen, gamma globulin and clotting factors.

Blood has three main functions: fighting disease, transporting nutrients and regulating body temperature. Destruction of RBCs (hemolysis) is a normal function of the body. RBCs have a normal life span of 120 days. A single unit of blood contains erythrocytes aging from one to 120 days. The spleen sequesters and destroys the RBCs that are old or damaged, while healthy, viable RBCs pass through the splenic bed.

Preparation of Blood

In the United States, a number of screening measures are used to attempt to ensure the safety of the donated blood supply. The medical history and physical health of volunteer blood donors are carefully scrutinized. In addition, potential donors are screened for possible contact with transfusion-transmissible diseases based on questioning about sexual behavior, drug use and travel to areas of endemic disease. The donated blood products are tested for compatibility and for the presence of markers of transmissible infectious agents (Table 1).¹

A patient receiving a blood transfusion must have a type and screen done before transfusion. Blood matching must be done to avoid transfusion reactions. A person can have one of the following four blood types: A, B, AB or O. This is based on two different test procedures: red cell grouping (forward grouping) and serum grouping (reverse grouping). The blood group is identified from the reaction of a person's red cells with blood grouping sera anti-A and anti-B. A person's serum is tested with known Group A₁ and Group B red cells to demonstrate the presence or absence of anti-A or anti-B (Table 2). A positive reaction is interpreted by visible agglutination with manipulation of the tubes or microscopically on a slide.

The D or Du antigen present on the RBCs determines the Rh factor. An Rh-positive person possesses the D or Du antigen. An Rh-negative person does not possess the D or Du antigen. An Rh-positive recipient should receive Rh-positive blood, but may receive Rh-negative blood in special circumstances. An Rh-negative recipient should receive Rh-negative blood to avoid immunizing the recipient to the D antigen.

If no antibody has been detected, and no record exists of the previous presence of a clinically significant antibody, only demonstration of ABO compatibility between the donor unit and recipient is required (Table 3).² Compatibility can be demonstrated by either an immediate spin cross-match or a computer cross-match.² The immediate spin cross-match tests the patient's serum for antibodies against antigens on the donor's red blood cells.³ The conditions for computer cross-match are outlined in the American Association of Blood Banks Standards.⁴

Whole Blood

Whole blood contains erythrocytes, leukocytes and platelets suspended in plasma. Whole blood must be ABO-identical for transfusion. One unit of whole blood should raise the hemoglobin by 1 g/dL and the hematocrit by 3%. In the past, whole blood had been indicated for severe blood loss when hypovolemia is suspected. It is still acceptable but not required. Whole blood is not as useful and economical as component therapy.⁵ In the United States, whole blood essentially is unavailable in emergency departments.⁶

Packed Cells

RBCs (packed cells) are produced when the plasma is removed from whole blood. One unit of RBCs will raise the hemoglobin by 1 g/dL and the hematocrit by 3%. Signs and symptoms and a physical assessment of the patient indicate whether the patient needs a transfusion. In stable perioperative patients without evidence of tissue hypoxia, a transfusion of less than 7 g/dL of hemoglobin is warranted.¹ In current practice, most hospital transfusion committees regard a hemoglobin value of 7 to 8 g/dL as a threshold that requires no justification for transfusion.¹

Leukocyte-Poor Blood Products

In leukocyte-poor (leukocyte-reduced) blood products, the blood is centrifuged, and the top layer known as the buffy coat is removed. About 70% to 80% of the leukocytes will be removed with the buffy coat. Indications for leukocyte removal are the development of an immune reaction to antigens on "foreign" transfused leukocytes that constitutes the great majority of febrile nonhemolytic transfusion reactions.⁷ Removal of leukocytes helps prevent microaggregates of white blood cells, fibrin, platelets and RBC debris that form in stored blood.⁷ It also helps prevent HLA alloimmunization, nonhemolytic febrile reactions, transmitting cytomegalovirus (CMV) and benefits neonates and immunocompromised patients.

Washed RBCs

Washed RBCs are prepared by washing the blood cells with saline. Washing blood cells removes donor antibodies and is useful in IgA immune reactions.⁷ It is indicated for patients with paroxysmal nocturnal hemoglobinuria. The blood must be infused within 24 hours after washing; otherwise it must be discarded. Washing RBCs removes about 70% to 90% of all white blood cells (WBCs).

Frozen RBCs

Frozen RBCs are obtained by adding glycerol to packed cells before freezing them. Frozen RBCs can be stored for up to 10 years. The glycerol must be removed before the cells can be infused. The advantage of freezing RBCs is the ability to stockpile unusual antigenic phenotypes and obtain a large inventory of units. Freezing removes about 95% of the total WBCs. Frozen RBCs should be transfused within 24 hours after thawing.

Irradiated RBCs

Irradiation of blood products includes platelet concentrates, whole blood, various RBCs and granulocyte concentrates. Irradiation of blood is indicated for patients at risk for graft-versus-host disease from transfusion.

CMV-Negative Blood

To prevent transmission of CMV infection, blood components from random donors are tested for CMV antibodies. Screened CMV blood products are reserved for those at risk for CMV infection. These include CMV-seronegative pregnant women, premature infants born to CMV-seronegative mothers, CMV-seronegative recipients of allogenic bone marrow transplants from CMV-seronegative donors and CMV-seronegative patients with AIDS.⁸

Leukocyte-Depleting Filters

Blood filters are more efficient in removing leukocytes and debris. Filters remove 99.9% of WBCs from blood products. The filter is hung at bedside and decreases the need for washed blood cells. Filters should be replaced after one to two units have been transfused.

Platelets

Platelet transfusions are administered to prevent or treat bleeding in thrombocytopenic patients and patients with inherited platelet defects.¹ Most prophylactic transfusions are for counts less than 20,000/µL. Bleeding patients may be transfused at platelet counts much higher than that. Unless patients hemorrhage, platelets should not be transfused when diagnosed with immune thrombocytopenic purpura, thrombotic thrombocytopenic purpura and hemolytic uremic syndrome. Platelets can be given as pooled concentrates or apheresis products. Pooled platelets need to be transfused within four hours. Each platelet unit contains about 5.5 x 10¹¹ platelets. A single unit will increase the platelet count about 10,000 in a 70 kg patient. A platelet count should be obtained one hour after transfusion. An accurate way of measuring the platelet count is by the corrected count increment (CCI):

CCI = post-transfusion platelet count — pre-transfusion platelet count/number of platelets transfused by 10¹¹ x body surface area (m²)

A CCI value of at least 5,000 should be seen.

Fresh Frozen Plasma

Plasma is separated from whole blood and stored at -18 degrees C within eight hours of collection. Once thawed, fresh frozen plasma (FFP) is stored at 1 degree C to 6 degrees C and must be transfused within 24 hours. FFP is most frequently transfused to replenish multiple coagulation factors in patients with documented coagulation abnormalities who are bleeding or at risk of bleeding during surgery.¹ FFP is used for replacement of individual coagulation factors that are not available as concentrates (factors II, V, X and XI) and management of thrombotic thrombocytopenic purpura.¹ FFP is occasionally used to replace hemostatic regulatory proteins such as antithrombin III, protein C or protein S.¹ FFP also is given to patients who are bleeding while on Coumadin with vitamin K deficiency or before vitamin K reverses Coumadin's effect.

Cryoprecipitate

Cryoprecipitate is indicated for the treatment of factor XIII deficiency and fibrinogen deficiency. One unit of cryoprecipitate per 5 kg will increase fibrinogen by approximately 75 mg/dL.¹ It is used as an alternative treatment for von Willebrand's disease and hemophilia A (factor VIII:C deficiency). One unit of cryoprecipitate raises the factor level by 40 U/dL for each 10 kg of body weight.¹ Cryoprecipitate must be used within six hours of thawing and four hours after pooling.

Autologous Blood

Autologous blood is any blood component that was donated by the intended recipient. Some advantages include that it eliminates transmission of infectious disease; eliminates the risk of alloimmunization to erythrocyte, leukocyte, platelet or protein antigens; eliminates risk of graft-versus-host disease; and eliminates risk of febrile, hemolytic or allergic reactions.⁹

Directed Donation

Directed donation is when a patient requests donations, usually from a family member or friend, of blood or blood components for transfusion, if warranted. Donors are screened just like any other volunteer donors, except the units are labeled for a specific recipient.⁹ Direct donors don't appear to be any safer than volunteer donors.

Conclusion

The administration of blood products and the management of bleeding disorders are important therapeutic modalities employed by clinicians caring for patients with a wide variety of acute and chronic problems.¹⁰ Clinicians make their decisions by weighing the benefits and risks for each patient. The risk of transmitting diseases by blood components has decreased greatly in recent years, mainly because of new methods to detect infectious disease markers in donor blood.¹¹ In the near future, blood safety is expected to increase even further, since nucleic acid amplification technology likely will be adapted for detection of the RNA of HIV and hepatitis C virus in donor blood.¹¹

Helene DiCaro is a pediatric physician assistant for Dr. James DeLeo in Coral Springs, Fla.

References

1. Rakel RE, Bope ET, eds. Conn's Current Therapy 2002. Philadelphia, Pa: WB Saunders Co; 2002:450-455.

2. Lee GR, Foerster J, Lukens J, et al, eds. Wintrobe's Clinical Hematology. 10th ed. Baltimore, Md: Lippincott Williams & Wilkins Co; 1999:832-834.

3. Blinder MA. Transfusion therapy. In: Ahya SN, Flood K, Paranjothi S, eds. The Washington Manual of Medical Therapeutics. 30th ed. Baltimore, Md: Lippincott Williams & Wilkins Co; 2001:425-428.

4. Standards for Blood Banks and Transfusion Services. 17th ed. Bethesda, Md: American Association of Blood Banks: 1996.

5. In: Marx J, Hockberger RS, Walls R, et al, eds. Rosen's Emergency Medicine: Concepts and Clinical Practice. 5th ed. St Louis, Mo: Mosby-Year Book; 2002:48-52.

6. Fakhry SM, Sheldon GF. Blood administration, risks, and substitutes. Adv Surg. 1995;28:71-92.

7. Ravel R. Clinical Laboratory Medicine: Clinical Applications of Laboratory Data. 6th ed. St Louis, Mo: Mosby-Year Book; 1995:123-130.

8. Sayers MH, Anderson KC, Goodhough LT, et al. Reducing the risk for transfusion-transmitted cytomegalovirus infection. Ann Intern Med. 1992;116:55-62.

9. Technical Manual of the American Association of Blood Banks. 11th ed. Bethesda, Md: American Association of Blood Banks: 1993.

10. Fakhry SM, Rutherford EJ, Sheldon GF. Hematologic principles in surgery. In: Townsend CM, Beauchamp DR, Evers M, et al, eds. Sabiston Textbook of Surgery. 16th ed. WB Saunders Co. 2001:68-78.

11. Szymanski IO. Transfusion therapy in general practice. In: Noble J, Greene HL II, Levinson W, et al, eds. Textbook of Primary Care Medicine. 3rd ed. St Louis, Mo: Mosby-Year Book; 2000:1053-1058.

http://physician-assistant.advanceweb.com/editorial/content/editorial.aspx?CC=152880

---

Add this page to your favourite Social Bookmarking websites;

Set as favorite

Email this

Hits: 640

Comments (0)

Write comment

Name

Email

Comment

smaller | bigger

Subscribe via email (registered users only)

I have read and agree to the Terms of Usage.

Add Comment