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In the US, the collection, storage, and transport of blood and its components are standardized and regulated by the FDA, the AABB (formerly known as the American Association of Blood Banks), and sometimes by state or local health authorities. Donor screening includes an extensive questionnaire and health interview; measurement of temperature, heart rate, and BP; and Hb determination. Some potential donors are deferred either temporarily or permanently (see Table: Some Reasons for Blood Donation Deferral or Denial). Criteria for deferral protect prospective donors from possible ill effects of donation and recipients from disease. Whole blood donations are limited to once every 56 days whereas apheresis RBC donations (donations of twice the usual amount of RBCs in one sitting) are limited to once every 112 days. Apheresis platelet donations are limited to once every 72 h with a maximum of 24/yr. With rare exceptions, blood donors are unpaid. (See also the American Red Cross for information regarding donor eligibility.)
Some Reasons for Blood Donation Deferral or Denial
In standard blood donation, about 450 mL of whole blood is collected in a plastic bag containing an anticoagulant preservative. Whole blood or packed RBCs preserved with citrate-phosphate-dextrose-adenine may be stored for 35 days. Packed RBCs may be stored for 42 days if an adenine-dextrose-saline solution is added.
Autologous donation, which is use of the patient’s own blood, is less preferred as a method of transfusion. When done before elective surgery, up to 3 or 4 units of whole blood or packed RBCs are collected in the 2 to 3 wk preceding surgery. The patient is then given iron supplements. Such elective autologous donation may be considered when matched blood is difficult to obtain because the patient has made antibodies to red cell antigens or has a rare blood type . Special blood salvage procedures are also available for collecting and autotransfusing blood shed after trauma and during surgery.
Donor blood testing includes ABO and Rh0(D) antigen typing, antibody screening, and testing for infectious disease markers (see Table: Infectious Disease Transmission Testing).
Infectious Disease Transmission Testing
Compatibility testing tests the recipient’s RBCs for antigens A, B, and Rh0(D); screens the recipient’s plasma for antibodies against other RBC antigens; and includes a cross-match to ensure that the recipient’s plasma is compatible with antigens on donor RBCs. Compatibility testing is done before a transfusion; however, in an emergency, testing is done after releasing blood from the blood bank. It can also help in diagnosing transfusion reactions.
ABO typing of donor and recipient blood is done to prevent transfusion of incompatible RBCs (see Figure: Compatible RBC types.). As a rule, blood for transfusion should be of the same ABO type as that of the recipient. In urgent situations or when the correct ABO type is in doubt or unknown, type O Rh-negative packed RBCs (not whole blood—see Complications of Transfusion : Acute hemolytic transfusion reaction (AHTR), for Acute Hemolytic Transfusion Reaction), which contains neither A nor B antigens, may be used for patients of any ABO type.
Rh typing determines whether the Rh factor Rh0(D) is present on (Rh-positive) or absent from (Rh-negative) the RBCs. Rh-negative patients should always receive Rh-negative blood except in life-threatening emergencies when Rh-negative blood is unavailable. Rh-positive patients may receive Rh-positive or Rh-negative blood. Occasionally, RBCs from some Rh-positive people react weakly on standard Rh typing (weak D, or Du, positive), but these people are still considered Rh-positive.
Antibody screening for unexpected anti-RBC antibodies is routinely done on blood from prospective recipients and prenatally on maternal specimens. Unexpected anti-RBC antibodies are specific for RBC blood group antigens other than A and B [eg, Rh0(D), Kell (K), Duffy (Fy)]. Early detection is important because such antibodies can cause serious hemolytic transfusion reactions or hemolytic disease of the newborn (see Perinatal Anemia : Hemolysis), and they may greatly complicate compatibility testing and delay procurement of compatible blood.
Indirect antiglobulin testing (the indirect Coombs test) is used to screen for unexpected anti-RBC antibodies. This test may be positive in the presence of an unexpected blood group antibody or when free (non-RBC–attached) antibody is present in autoimmune hemolytic anemias (see Autoimmune Hemolytic Anemia ). Reagent RBCs are mixed with the patient’s plasma or serum, incubated, washed, tested with antihuman globulin, and observed for agglutination. Once an antibody is detected, its specificity is determined. Knowing the specificity of the antibody is helpful for assessing its clinical significance, selecting compatible blood, and managing hemolytic disease of the newborn.
Direct antiglobulin testing (the direct Coombs test) detects antibodies that have coated the patient’s RBCs in vivo. It is used when immune-mediated hemolysis is suspected. Patients’ RBCs are directly tested with antihuman globulin and observed for agglutination. A positive result, if correlated with clinical findings, suggests autoimmune hemolytic anemia, drug-induced hemolysis, a transfusion reaction, or hemolytic disease of the newborn.
Antibody titration is done when a clinically significant, unexpected anti-RBC antibody is identified in the plasma of a pregnant woman or in a patient with cold autoimmune hemolytic anemia (see Autoimmune Hemolytic Anemia ). The maternal antibody titer correlates fairly well with the severity of hemolytic disease in the incompatible fetus and is often used to guide treatment in hemolytic disease of the newborn along with ultrasonography and amniotic fluid study.
The addition of a cross-match to ABO/Rh typing and antibody screening increases detection of incompatibility by only 0.01%. Therefore, many hospitals are doing computerized electronic cross-matches rather than physical cross-matches in patients who have negative antibody screening. If the recipient has a clinically significant anti-RBC antibody, donor blood is restricted to RBC units negative for the corresponding antigen; further testing for compatibility is done by combining recipient plasma, donor RBCs, and antihuman globulin. In recipients without clinically significant anti-RBC antibodies, an immediate spin cross-match, which omits the antiglobulin phase, confirms ABO compatibility.
Emergency transfusion is done when not enough time (generally < 60 min) is available for thorough compatibility testing because the patient is in hemorrhagic shock. When time permits (about 10 min is needed), ABO/Rh type-specific blood may be given. In more urgent circumstances, type O RBCs are transfused if the ABO type is uncertain, and Rh-negative blood is given to females of child-bearing age if the Rh type is uncertain; otherwise, either Rh-negative or Rh-positive blood can be used.
“Type and screen” may be requested in circumstances not likely to require transfusion, as in elective surgery. The patient’s blood is typed for ABO/Rh antigens and screened for antibodies. If antibodies are absent and the patient needs blood, ABO/Rh type specific or compatible RBCs may be released without the antiglobulin phase of the cross-match. If an unexpected antibody is present, full testing is required.
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