The Solid Phase Adherence Assay (SPAA)

SPAA for antibody identification uses dried red cells that have been bound to the surfaces of polystyrene microtitration strip wells, and which capture IgG antibodies (if present) in patient sera. The test is a modified IAT that detects antibody by addition of anti-IgG-coated red cells.

Immucor's Capture-R Ready ScreenTM is a commercial solid phase system distributed in Canada by Dominion Biologicals that uses strip micro wells which are coated with dried antibody screen cells. Automated systems using SPAA include Immucor's ABS 2000 and Rosys Plato.

Principle

The SPAA for antibody detection uses red cell membranes that have been bound to the surfaces of polystyrene microtitration strip wells, and which capture IgG antibodies in patient sera.

• Patient plasma or serum and an enhancement solution such as LISS are added to wells coated with red cell membranes (screen cells).
• After incubation at 37oC, unbound IgG is washed away (as in standard antiglobulin tests).
• Anti-IgG-coated indicator red cells are added.
• Tests are centrifuged and read.
• If patient IgG antibodies have attached to the cell membranes, the anti-IgG-coated indicator red cells form anti-IgG-IgG complexes. As a result, the indicator cells adhere to the wells as a second immobilized cell layer and form a dispersed conflux ("lawn") of cells, constituting a positive test.
• Conversely, in negative tests, the indicator cells pellet to the bottom of the wells forming a distinct, smaller cell button.

Types

• red cell assays
• platelet assays (IgG anti-platelet antibodies)
• infectious disease assays (screen for anti-CMV)

Applications

• antibody screening
• antibody identification
• antigen typing

Types of Antibodies Detected

IgG antibodies

Advantages

• increased sensitivity
• automation possible for high volume and batch testing
• claims to have faster test performance times thereby saving technologist time
• test results may be stored for confirmation reading by a supervisor or staff on a different shift
• elimination of microscopic reading resulting in more objective interpretation of test results
• no red cell resuspension resulting in a more standardized procedure

Disadvantages

• relatively expensive start-up costs for automated systems