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Blood Collection

By

Ravindra Sarode

, MD, The University of Texas Southwestern Medical Center

Last full review/revision May 2020| Content last modified May 2020
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More than 21 million units of blood components are transfused yearly in the US, from about 7 million volunteer donors (1 General reference More than 21 million units of blood components are transfused yearly in the US, from about 7 million volunteer donors (1). Although transfusion is probably safer than ever, risk (and the public’s... read more ). Although transfusion is probably safer than ever, risk (and the public’s perception of risk) mandates informed consent whenever practical.

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 blood pressure; and Hb determination. Some potential donors are deferred either temporarily or permanently (see table Some Reasons for Blood Donation Deferral or Denial Some Reasons for Blood Donation Deferral or Denial More than 21 million units of blood components are transfused yearly in the US, from about 7 million volunteer donors (1). Although transfusion is probably safer than ever, risk (and the public’s... read more ). 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 red blood cell (RBC) donations (donations of twice the usual amount of RBCs in one sitting, with the separated plasma being returned to the donor) are limited to once every 112 days. Apheresis platelet donations are limited to once every 72 hours with a maximum of 24/year. With rare exceptions, blood donors are unpaid. (See also the American Red Cross for information regarding donor eligibility.)

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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 weeks 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.

General reference

Pretransfusion Testing

Donor blood testing includes

Compatibility testing tests the recipient’s RBCs for antigens A, B, and Rho(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.

The addition of a cross-match to ABO/Rh typing and antibody screening increases detection of incompatibility by only 0.01%. Therefore, many hospitals do computerized electronic cross-matches rather than physical cross-matches in a test tube 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 minutes) is available for thorough compatibility testing because the patient is in hemorrhagic shock Shock Shock is a state of organ hypoperfusion with resultant cellular dysfunction and death. Mechanisms may involve decreased circulating volume, decreased cardiac output, and vasodilation, sometimes... read more . When time permits (about 10 minutes 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 O 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.

ABO and Rho typing

ABO typing of donor and recipient blood is done to prevent transfusion of incompatible RBCs (see figure Compatible RBC types Compatible RBC types More than 21 million units of blood components are transfused yearly in the US, from about 7 million volunteer donors (1). Although transfusion is probably safer than ever, risk (and the public’s... read more ). 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 Acute Hemolytic Transfusion Reaction Acute hemolytic transfusion reaction (AHTR) The most common complications of transfusion are Febrile nonhemolytic reactions Chill-rigor reactions The most serious complications, which have very high mortality rates, are Acute hemolytic... read more ), which contains neither A nor B antigens, may be used for patients of any ABO type.

Compatible RBC types

Compatible RBC types

Rh typing determines whether the Rh factor Rho(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

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, Rho(D), Kell (K), Duffy (Fy)]. Early detection is important because such antibodies can cause serious hemolytic transfusion reactions Acute hemolytic transfusion reaction (AHTR) The most common complications of transfusion are Febrile nonhemolytic reactions Chill-rigor reactions The most serious complications, which have very high mortality rates, are Acute hemolytic... read more or hemolytic disease of the newborn Blood loss Anemia is a reduction in red cell mass or hemoglobin and is usually defined as hemoglobin or hematocrit > 2 standard deviations below the mean for age. Some authorities also consider a relative... read more , 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 (see figure Indirect antiglobulin (indirect Coombs) test Indirect antiglobulin (indirect Coombs) test More than 21 million units of blood components are transfused yearly in the US, from about 7 million volunteer donors (1). Although transfusion is probably safer than ever, risk (and the public’s... read more ). 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 Autoimmune Hemolytic Anemia Autoimmune hemolytic anemia is caused by autoantibodies that react with red blood cells at temperatures ≥ 37° C (warm antibody hemolytic anemia) or 37° C (cold agglutinin disease). Hemolysis... read more 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.

Indirect antiglobulin (indirect Coombs) test

The indirect antiglobulin (indirect Coombs) test is used to detect IgG antibodies against red blood cells (RBCs) in a patient's plasma. The patient's plasma is incubated with reagent RBCs; then Coombs serum (antibodies to human IgG, or human anti-IgG) is added. If agglutination occurs, IgG antibodies (autoantibodies or alloantibodies) against RBCs are present. This test is also used to determine the specificity of an alloantibody.

Indirect antiglobulin (indirect Coombs) test

Direct antiglobulin testing (the direct Coombs test) detects antibodies that have coated the patient’s RBCs in vivo (see figure Direct antiglobulin (direct Coombs) test Direct antiglobulin (direct Coombs) test More than 21 million units of blood components are transfused yearly in the US, from about 7 million volunteer donors (1). Although transfusion is probably safer than ever, risk (and the public’s... read more ). 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 and laboratory indicators of hemolysis, suggests autoimmune hemolytic anemia, drug-induced hemolysis, a transfusion reaction, or hemolytic disease of the newborn.

Direct antiglobulin (direct Coombs) test

The direct antiglobulin (direct Coombs) test is used to determine whether red blood cell (RBC)-binding antibody (IgG) or complement (C3) is present on RBC membranes. The patient's RBCs are incubated with antibodies to human IgG and C3. If IgG or C3 is bound to RBC membranes, agglutination occurs—a positive result. A positive result suggests the presence of autoantibodies to RBCs. A false-positive can occur and does not always equate with hemolysis. Thus, results should always be correlated with the clinical signs and symptoms.

Direct antiglobulin (direct Coombs) test

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 agglutinin disease Autoimmune Hemolytic Anemia Autoimmune hemolytic anemia is caused by autoantibodies that react with red blood cells at temperatures ≥ 37° C (warm antibody hemolytic anemia) or 37° C (cold agglutinin disease). Hemolysis... read more 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.

Infectious disease testing

Donated blood products are tested for the presence of a number of infectious agents.

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More Information

The following are some English-language resources that may be useful. Please note that THE MANUAL is not responsible for the content of these resources.

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