What lab test should be ordered to determine blood type?

Blood Type Testing: Laboratory Tests and Clinical Significance

To determine a person's blood type, an ABO and Rh blood typing test should be ordered, which is typically performed twice to ensure accuracy. 1

Primary Blood Typing Tests

• ABO blood typing is the fundamental test that determines whether a person's blood contains A antigens, B antigens, both (AB), or neither (O) 1, 2
• Rh typing determines whether the Rh(D) antigen is present (Rh-positive) or absent (Rh-negative) 1, 2
• Both tests are typically performed together as a standard blood typing panel 3

Testing Methodology

• The most common methods for blood typing in clinical laboratories include:

  • Hemagglutination tests (direct agglutination with specific antisera) 3
  • Microcolumn gel tests (for more sensitive detection) 3
  • Reverse grouping to confirm ABO type by testing for expected isoagglutinins 4

• For donor candidates and in critical clinical scenarios, blood typing should be performed twice to minimize the risk of errors 1

Additional Testing Considerations

• Blood group A subtype testing should be performed when donation or transfusion is planned for recipients with anti-A antibodies 1
• ABO blood typing is often accompanied by antibody screening tests to detect unexpected antibodies that could cause transfusion reactions 4
• In cases of suspected hemolytic disease or blood type discrepancies, additional testing such as direct antiglobulin test (DAT or direct Coombs' test) may be required 2

Clinical Significance and Applications

• Blood typing is essential for:

  • Safe blood transfusions to prevent potentially fatal transfusion reactions 3
  • Organ and tissue transplantation compatibility assessment 3
  • Maternal-fetal medicine to identify risk of hemolytic disease of the newborn 5, 2
  • Determining eligibility for kidney paired donation in cases of ABO incompatibility 1

• Blood type has been associated with susceptibility to various diseases, though this information is primarily used in research rather than clinical decision-making 6

Common Pitfalls and Considerations

• Factors that can complicate accurate blood typing include:

  • Recent massive transfusions causing mixed cell populations 7
  • Certain medications interfering with testing results 7
  • Hematopoietic stem cell transplantation potentially changing blood type 7
  • Weak expression of antigens in certain subgroups 3

• In emergency situations requiring immediate transfusion before complete typing can be performed, type O-negative blood (universal donor) may be used, but complete typing should be performed as soon as possible 1

Documentation Requirements

• Blood typing results should be clearly documented in the patient's medical record 2
• For potential organ donors, blood typing should be documented twice in the medical record to prevent errors 1