The fundamental purpose of testing donated blood is to safeguard the health of the transfusion recipient and ensure the blood product is compatible. This process is a multilayered system of checks and laboratory analyses designed to maintain the integrity of the blood supply. This rigorous screening begins before the donation and continues with advanced laboratory testing after the blood is collected. The goal is to eliminate the risk of transmitting infectious diseases while correctly identifying the blood’s characteristics for safe use.
Donor Health Screening Before Donation
The initial step involves a health screening performed before the donation, designed to protect both the donor and the potential recipient. A staff member reviews a detailed medical history questionnaire asking about recent travel, medications, and lifestyle behaviors that could affect blood safety. This confidential history is the first line of defense against accepting blood that might pose an infection risk or compromise the donor’s well-being.
A physical check follows the questionnaire to ensure the donor is healthy enough to give blood. This includes checking the donor’s pulse, blood pressure, and temperature. A small blood sample is also analyzed to measure the hemoglobin or hematocrit level, confirming enough red blood cells are present to prevent donor anemia. Only after passing both the health history and the physical check is the donor eligible to proceed with collection.
Mandatory Infectious Disease Testing
Once the blood unit is collected, it moves to the laboratory for extensive testing focused on ruling out transfusion-transmissible infections (TTIs). Every donation is subjected to comprehensive screening for a specific panel of pathogens that could be passed to a patient. This mandatory testing is essential for ensuring the safety of the final blood product.
The core screening panel includes tests for Human Immunodeficiency Virus (HIV-1 and HIV-2), Hepatitis B Virus (HBV), and Hepatitis C Virus (HCV). Blood is also tested for other serious infections such as Syphilis and West Nile Virus (WNV). Depending on the region and current outbreaks, pathogens like Zika virus or Trypanosoma cruzi (Chagas disease) may also be screened. These tests look for both the presence of the pathogen itself and the antibodies the donor’s immune system has produced in response.
Advanced technologies, like Nucleic Acid Testing (NAT), are employed to detect the genetic material of viruses such as HIV, HCV, and HBV. NAT can identify the presence of a virus much sooner than antibody tests, during the “window period” before the body has mounted an immune response. This rapid detection significantly reduces the risk of transmitting infection through transfusion. The combination of antigen, antibody, and NAT screening provides a robust system for pathogen detection.
Blood Grouping and Rh Factor Determination
Beyond infectious disease screening, every unit of donated blood must be precisely typed to ensure compatibility with a recipient. This process involves determining the ABO blood group and the Rhesus (Rh) factor. The ABO system classifies blood into four types—A, B, AB, and O—based on the presence or absence of specific antigens on the surface of the red blood cells.
The Rh factor is the second most important classification, determined by the presence or absence of the D antigen. Its presence makes the blood type positive (+), and its absence makes it negative (-). Knowing both the ABO group and the Rh factor results in one of the eight common blood types, such as O-positive or A-negative. This information is essential because receiving incompatible blood can trigger a severe immune reaction in the patient.
A person with type A blood, for example, has anti-B antibodies, meaning they can only safely receive A or O blood. The specific pairing of donor and recipient blood types is necessary because the recipient’s immune system will attack red blood cells with unfamiliar antigens. The testing process confirms the specific type of the donated unit to ensure it is correctly labeled for appropriate transfusions.
Notification and Management of Test Results
If any infectious disease or typing tests yield a non-negative or reactive result, the blood unit is immediately quarantined and prevented from being used for transfusion. This precautionary measure is taken even if the initial test result is not fully confirmed, prioritizing patient safety. Units confirmed positive for infectious diseases are typically disposed of according to strict safety protocols.
The blood center attempts to notify the donor of the abnormal test results and their deferral status. Donors who test positive for certain diseases, such as HIV, are usually contacted by telephone in addition to receiving a registered letter. This notification process includes informing the donor of the specific test results and providing information about medical follow-up and counseling services.
A donor who tests positive for a transfusion-transmissible infection is typically placed on a donor deferral registry. This registry ensures they cannot donate again until they meet specific re-entry criteria, or are permanently prevented from future donations. This system is a final security measure to protect the blood supply and connect the donor with important health information.