The main limitation of using blood groups to identify people is that they are much more effective at eliminating people and much less effective at positively identifying people.
For example, about 37% of Americans are type O+. If you are trying to find out who committed a crime and you know that they person who did the crime has O+ blood, you have not gone very far to identify the person who actually did commit the crime. But you can eliminate people. For example, I do not have this type of blood, so I did not do it.
Result of determination of blood group of a person should be read by two people and possibly be confirmed on a second sample of blood, in order to avoid reading errors which are due to errors in technique.
The reading errors occured in determination of blood group are:
- Dirty glass;
- Bacterial contamination;
- Presence of micro-clots (false agglutination);
- there are not fulfilled: the proportion of red blood and serum; contradictory agglutination;
Errors occured during reading:
- reading late - dry edges (false agglutination);
- reading early - no agglutination or poor agglutination.