How to Determine a Patient's Blood Type
Blood typing is performed through pre-transfusion laboratory testing that determines both ABO and RhD status using serologic methods, requiring a properly collected and labeled blood sample sent to the transfusion service. 1
Standard Blood Typing Procedure
Sample Collection Requirements
- Collect blood sample at the patient's bedside with proper identification verification using at least two unique identifiers: surname, forename, date of birth, and hospital unique identification number 1
- The patient must wear an identification band with matching information 1
- Sample must be hand or electronically-labeled at the patient's side by appropriately trained personnel 1
- Avoid "wrong-blood-in-tube" events which represent a critical safety risk for ABO incompatibility 1
Laboratory Testing Methods
Pre-transfusion procedures determine the patient's ABO and Rhesus D (RhD) status through two complementary tests 1:
- Forward typing: Tests red blood cells for A and B antigens 2
- Reverse typing: Tests plasma for anti-A and anti-B antibodies 2
- Both results must agree to confirm the blood type 2
Standard blood typing typically takes approximately 45 minutes to complete 1
Sample Validity Considerations
- If the patient received a transfusion or was pregnant within the previous 3 months, the sample is only valid for 72 hours from collection to subsequent transfusion 1
- Two samples may be required unless a suitable "historical" sample exists on file with adequate patient identification 1
- Historical samples can serve as the "group-check" sample if patient identification confirms it's from the same patient 1
Emergency Situations
Rapid Blood Typing
In emergencies, grouping can be performed in approximately 10 minutes (not including transfer time), allowing issue of group-specific blood 1
When Blood Type is Unknown
- Group O RhD negative is the blood group of choice for immediate emergency transfusion when blood type is unknown 1
- Group O RhD positive red cells are acceptable for male patients to preserve O RhD negative inventory 1
- Recent evidence shows transfusing emergency patients with unknown blood type with O RhD+ has a low risk (3-6%) of inducing anti-D antibodies 3
Unknown Patient Identity
When patient identity is unknown, use an alternative identification system with 1:
- At least one unique identifier (e.g., randomly generated seven-digit number with prefix)
- Naming convention from edited phonetic alphabet
- Date-of-birth system
- Patient's sex
- Once identity is known, attach new identification band and collect new transfusion sample 1
Extended Typing Considerations
Beyond ABO/RhD
For patients requiring ongoing transfusion support, particularly those with sickle cell disease, extended red cell antigen profiling beyond ABO/RhD typing is recommended 1:
- Rh antigens (C/c, E/e) and K antigen typing reduces alloimmunization risk 1
- More extensive profiles including Jka/Jkb, Fya/Fyb, M/N, and S/s can expedite antibody identification when patients develop positive antibody screens 1
Typing Methods
- Serologic typing is the standard method using hemagglutination or microcolumn gel tests 4
- Molecular genotyping provides more comprehensive and accurate results, particularly for C antigen determination and Fyb matching, though it requires longer turnaround time as a referral test 1
- DNA-based typing overcomes limitations when recent transfusion or interfering antibodies are present 1
Common Pitfalls to Avoid
- Never proceed with transfusion without proper patient identification - this is the most critical safety step 1
- Recognize that ABO discrepancies can occur when forward and reverse typing don't match, requiring resolution before transfusion 2
- Be aware that hemoglobin concentration may remain falsely elevated despite significant blood loss if fluid resuscitation is inadequate 1
- In massive bleeding, clinical signs of transfusion reactions may be difficult to diagnose, but documentation should be double-checked if concerns arise 1