Back to List

Blood Compatibility Testing (Crossmatch)

A "type" includes a "front type" and a "back type". The "front type" determines which antigens ("flags") in the ABO blood group system are on the patient's red blood cells as follows:

A antigen only	Type A
B antigen only	Type B
A and B antigens	Type AB
Neither A or B	Type O

The "back type" identifies the isohemagglutinin (naturally occurring antibody) in the patient's serum and should correspond to the antigens found on the red blood cells as follows:

anti-B	Type A
anti-A	Type B
anti-A and anti-B	Type O
neither anti-A or anti-B	Type AB

In addition, RBC's are Rh typed and identified as "D" positive or negative.

A "screen" looks for unexpected red cell alloantibodies which may form following pregnancy or prior transfusions. If the screen is positive, the antibody is identified and 2 units lacking the corresponding antigen are crossmatched for the patient. The physician is also notified. Antibody identification can be complicated and take more than a day to complete.

A "type and cross" determines compatibility between patient serum and donor red blood cells.

1. A full crossmatch procedure takes about 45 minutes to complete and cannot be shortened.
2. Units are refrigerated until used.
3. A unit of blood must be properly labelled and the label MUST be checked before use.

Every unit crossmatched is removed from the general inventory and reserved for the patient for 72 hours. Units which are crossmatched unnecessarily will deplete Blood Bank inventories and can result in blood shortages, such as those which occurred in California after the earthquake. Blood shortages can result in cancellation of elective surgical procedures.

Blood will ordinarily not be released for transfusion until compatibility testing is completed.

However, under emergency conditions, blood products may be released without a crossmatch if the patient is in danger of dying if transfusion is delayed. In such cases, if the patient's blood type is not known, then group O Rh negative (O neg) blood can be released without compatibility testing.

In cases in which the patient's blood type is reliably known, then type-specific blood or RBC's of the same ABO and Rh group may be released.

Blood Preservation and Storage

Blood is collected as whole blood, as shown below:

Blood can be stored as whole blood (with all of the plasma present) or, much more commonly, as packed red blood cells (PRBC's) in which about 70% of the plasma has been removed. This is done by light centrifugation, as shown below:

The platelet rich plasma can then be expressed off, leaving packed red blood cells (PRBC's) as shown here:

Both whole blood and PRBC's can be stored for up to 42 days at 1 - 6 degrees C.

The plasma can be centrifuged heavily a second time to separate the platelet rich plasma, as shown below:

The supernatant plasma can be expressed into a third bag and stored as fresh frozen plasma (FFP). The remaining platelet rich plasma is utilized as a platelet pack, as shown below:

As can be seen in the above diagram, a single donation of whole blood has supplied three separate components (packed red blood cells, platelets, fresh frozen plasma) that can potentially benefit three different patients.

After the expiration date, rare or valuable blood units can be "rejuvenated" with a biochemical solution that restores much of the original biochemical environment of the RBC's. The "rejuvenated" units are "washed" with isotonic saline in an automated device and then can be transfused as a saline-red blood cell suspension within 2 to 4 hours, or these units can be stored glycerolized and frozen for up to 10 years.

Cryopreservation of RBC's is done to store special, rare RBC's for up to 10 years. The RBC's are first incubated in a 40% glycerol solution which acts as an "antifreeze" within the cells. The units are then placed in special sterile containers in a deep freezer at less than -60 degrees C.

Cryopreserved units are thawed and washed free of glycerol prior to use as saline suspended RBC's. These units must be used in 2 - 4 hours to prevent possible bacterial contamination. The washed units are depleted of plasma and leukocytes.

Cryopreserved blood can help to maintain stores of Rh negative blood, to provide units for persons with antibodies to high-incidence antigens or persons difficult to cross-match because of multiple alloantibodies and to provide plasma-free blood to persons with IgA deficiency.

Thus, the types of RBC products available are:

• Whole blood.
• Packed red blood cells (PRBC's)
• Leukocyte depleted RBC's: cryopreserved blood that is thawed and degylcerolized is depleted of leukocytes, but much better depletion can be obtained by filtering the blood through leukocyte-specific filters.
• Frozen, deglycerolized RBC's

Tests Performed

A number of laboratory tests must be completed before blood or blood products can be transfused:

• Determination of the blood type with a crossmatch.
• Screening for antibodies that may produce adverse effects if transfused.
• Screening for possible infectious agents that could be transmitted with transfusion.

The following tests are manadatory on all units of blood collected for transfusion:

• ABO group and Rh type
• Screening for blood-group antibodies
• Serologic test for syphilis
• Serologic tests for human retroviruses including:
  • HIV-1 antibody
  • HIV-2 antibody
  • HIV p24 antigen
  • HTLV I antibodies
• Serologic tests for hepatitis including:

  Hepatitis B surface antigen (HBsAg)

  Hepatitis B core antibody (HBcAb)

  Hepatitis C antibody

If, and only if, all of these markers are negative can blood be conveyed to the Blood Bank for storage until usage. A postive results for some of these tests may prevent further donation by that person. A person with such a test result will be notified by the donor center. Persons with a potential medical condition should see a physician and should not, under any circumstance, donate only to have blood tested. These measures are done to make the blood supply as safe as possible. The significant infectious diseases transmitted by transfusion and the risk of transmission (RT) in the U.S. are given below.

---

Transfusion Transmitted Diseases

Hepatitis B

Hepatitis B virus (HBV) is transmitted through parenteral and sexual exposure. The incubation time is a mean of 90 days with a range of 30 to 180 days.

Donor blood is routinely tested for HBsAg and HBcAb. There is no routine testing for hepatitis A, because it is rarely transmitted by blood products.

Recipients of blood products can also be infected with hepatitis delta, which is a defective RNA virus that needs a HBV superinfection to replicate.

Persons who have received a hepatitis B vaccination (recommended for all health care workers with patient contact) will have hepatitis B surface antibody present, but not HBsAg or HBcAb

Risk of transmission (RT) = 1/66,000 to 1:200,000

Hepatitis C

The route of transmission is parenteral, with sexual transmission lower than previously throught. The mean incubation time is 6 to 8 weeks.

Blood Bank testing for HCV started in 1990. At present, only testing for hepatitis C antibody is available.

Risk of transmission (RT) = 1/121,000

 

Human Immunodeficiency Virus (HIV)

In 1982 the first cases of AIDS obtained from blood or blood components were reported, but the etiology of the infections was not known at that time.

By 1983 changes occurred in the donor cirteria to exclude those at high risk for transmission of HIV.

The first testing of blood products for HIV started in 1985 and is a test to detect the presence of antibody directed against HIV. Testing for HIV p24 antigen was mandated in 1996.

Risk of transmission = 1/563,000 to 1/825,000

Human T-lymphocytotrophic Virus (HTLV-1).

HTLV-1 is a retrovirus that is endemic in Japan and the Caribbean. Implicated as causing adult T-cell leukemia/lymphoma and a neurological disorder similar to multiple sclerosis.

Blood is routinely screened for antibodies to HTLV-1.

Risk of transmission = 1/641,000 (but only 1-3% of seropositive individuals will develop disease).

Cytomegalovirus (CMV)

The prevalence of CMV antibody ranges from 50 to 80% of the population. Blood contaminated with CMV can cause problems in neonates or immunocompromised patients.

Potential problems in selected patient populations can be prevented by transfusing CMV negative blood or frozen, deglycerolized RBC's.

Donor blood is not routinely tested for CMV.

Malaria

Malaria is rarely transmitted by RBC products, although the number of transfusion associated cases of malaria is at an all-time high.

There are no practical laboratory tests available to test donor blood, so donors travelling to high risk malaria areas are excluded from donating blood for six months.

Others

Additional diseases which are rarely transmitted by blood products, but for which no routine cost-effective laboratory testing is available include:

• Babesiosis.
• Lyme disease.
• Chagas' disease.

Back to List