Manual tube testing is traditionally used for ABO typing. Reactions in this in vitro environment are the simplest, unpotentiated example of how ABO antigens and antibodies optimally react. The manual tube testing process is illustrated below.
Column agglutination, also referred to as gel testing, is a commonly used automated method for pretransfusion testing.
There are a number of reasons for its widespread usage:
- Ease of use. It is very easy to use gels cards, following designate protocol with regard to adding patient and reagent volumes.
- Ability to preserve reactions. Once testing is complete, the card may be sealed and stored for review hours after testing has been resulted.
- Ease of macroscopic visualization and interpretation.
An example of the gel method is shown in the image on the right.
Solid phase testing methods use modified microwells for the immobilization of human erythrocytes. Reagents are added to patient samples and the microwells are centrifuged in a specialized centrifuge. Red cells adhere to the well based upon the reaction between patient sample and reagent. In this methodology, the formation of a monolayer of red blood cells is indicative of a positive result. Conversely, a button formation at the bottom of the microwell is interpreted as a negative reaction.
Possible situations that can cause result interference with this method include:
- Residual fibrin from improperly anticoagulated samples
- Over or under-centrifugation
- Contaminated reagents