Applications

In general, enzyme tests have 4 uses:

1. To help detect and identify antibodies because they enhance them, e.g., weak Rh and Kidd antibodies.
2. To help identify a mixture of antibodies by denaturing some corresponding antigens, e.g., if a patient had anti-c and anti-Fy^a, his serum could agglutinate all cells in an IAT panel making identification difficult; but only anti-c would react in an enzyme panel.
3. To enhance the efficiency of autoabsorption of autoantibodies so that possible alloantibodies can be detected, e.g., both cold autoantibodies (anti-I) and warm autoantibodies (Rh) are enhanced by enzymes. If the patient's red cells are treated with an enzyme prior to autoabsorption, the autoantibodies will attach to the cells more efficiently.
4. Some Rh typing antisera require the addition of enzymes to work. The Red Cross sometimes uses these reagents.

Use of Enzymes in the Routine Blood Bank

As discussed, enzymes have various advantages and disadvantages. Because they denature certain antigens, they are never used as the sole method of antibody detection. Each lab must balance the pros and cons of enzymes in deciding if they will be used routinely as a secondary test in addition to the antiglobulin test.

Some labs use enzyme tests selectively. The main reason they are not used routinely is because they enhance cold IgM antibodies like autoanti-I. The types of situations/patients that enzyme tests may be appropriate for include the following:

1. pregnant women (because Rh antibodies react best in enzymes and are a common cause of HDN).
2. patients with warm AIHA (because warm autoantibodies may have specificity in the Rh system).
3. patients with positive DATs (same reason as #2 above).
4. investigation of a suspected delayed hemolytic transfusion reaction (because we want to detect weak Rh and Kidd antibodies, which are enhanced by enzymes).

Applications