Testing to Ensure the Safety of Donated Blood
In the blood bank laboratory, certain tests must be performed on all donated blood. In addition to typing blood to determine the donor's ABO blood group and Rh status, several screens are performed to ensure the safety of the blood. Screening is conducted for:
- Unexpected red blood cell antibodies that could cause reactions in the recipient, such as those made as a result of a previous transfusion or pregnancy
- Bacterial contamination in units of platelets
- Current and past transmissible infections; each unit of donated blood is tested for:
Additionally, the U.S. Food and Drug Administration (FDA) has directed blood collection facilities to screen all donated blood and blood components for the Zika virus. The FDA approved two investigational tests for this purpose. The tests were approved under an "investigational new device (IND)" protocol and did not go through the standard regulatory process prior to implementation, which can be time-consuming. The tests screen for the presence of the virus by detecting its genetic material (RNA). Units of blood that test positive for the virus are removed from the supply and not used for transfusions.
The FDA has also approved a test to detect blood infected with Chagas disease. The test is not yet mandatory, but many facilities have already begun screening all blood donors for this disease.
Testing for the infectious diseases in the bulleted list above often is done by antibody screening. However, newer tests for viruses are available that detect the genetic material of the viruses, which shortens the window of time in which the virus may be undetectable in a donor. Known as nucleic acid amplification testing (NAT), this methodology is being used routinely to screen donated blood for hepatitis and HIV and has helped improve the safety of the blood supply in this country.
Confirmatory tests are performed in duplicate if any test results are positive in order to rule out false positives. If both confirmatory test results are negative, the initial screening result may be considered a false positive. Depending on the facility and the guidelines used, the unit may then be released for use. Some facilities discard the unit regardless of the confirmatory test result.
Once the testing is completed, those units of blood that are free of infection are made available for transfusion when needed. Those in which infection is detected are discarded, and the donor is notified as well as prohibited from future blood donation.
It also is important to realize that there are some infectious diseases that are not or cannot be tested for at the present time, such as malaria. The potential for an infectious agent that will not be detected by testing to be present in a donated unit underscores the importance of donors reporting any transmissible infections they have had or may have been exposed to in the past.
Storing Blood Safely
Proper storage of whole blood and blood components is essential.
- Red blood cells must be stored under refrigeration and can be kept for a maximum of 42 days or frozen for up to 10 years.
- Platelets can be stored at room temperature for a maximum of 5 days.
- Fresh frozen plasma can be kept frozen for up to 1 year.
- Cryoprecipitate AHF made from fresh frozen plasma can be stored frozen for up to 1 year.
- Granulocytes (white blood cells) must be transfused within 24 hours of donation.