Anti D Antibody (ADA) Titer Test: Introduction, Principle, Procedure, Result

Anti D Antibody (ADA) Titer Test: Introduction, Principle, Procedure, Result Interpretation and Keynotes

Introduction of Anti D Antibody (ADA) Titer Test

Anti D Antibody also known as Rh typing antibody and its semi-quantitative determination is titer. ADA titer or Rh antibody titer is clinically significant in a pregnant woman who is Rh-negative and her husband Rh-positive. A rising of ADA titer indicates the possible occurrences, of hemolytic disease of the newborn (HDN).

Principle of ADA Titer Test

Antibody titration implies a serial dilution of the serum. Each dilution is tested against the corresponding antigen. The highest serum dilution where the agglutination detected is the titer.

Requirements for Anti D Antibody (ADA) Titer Test

Equipment and reagent required for ADA titer includes-

Test tubes (10× 100 mm)
Tube rack
Pasteur pipettes
Centrifuge
Incubator (37ºC)
5% saline suspension of Rh-positive cells
Normal Saline
22% bovine albumin
Sample-Blood (serum)
Microscope

Procedure of Anti D Antibody (ADA) Titer Test

Make serial serum dilutions as shown in the table.

Put 0.1 ml of normal saline in each tube.
Add 0.1 ml of serum in the first tube and mix well.
Transfer 0.1 ml of the contents from tube 1 to 2, mix well.
Continue this procedure till tube No. 9 and throw from the last tube 0.1 ml.
Put two drops of 22% bovine albumin in all the tubes, mix well.
Add one drop of 5% saline suspension of Rh-positive red cells in all the tubes, mix well.
Incubate the tubes at 37ºC for 30 minutes.
After completion of incubation, centrifuge at 1500 RPM for one minute.
Observe the tubes, macroscopically as well as microscopically for hemagglutination.
Follow the observation table.

Result Interpretation of Anti D Antibody Titer

No agglutination: ADA Negative
Agglutination: ADA Positive
The tube in which agglutination: Indicate titer e.g. agglutination in tube no 4 and therefore titer is 1: 16.

Keynotes on ADA test

No fasting sample and other special preparations are required.
If agglutination is observed in the last tube (dilution 1:512) then it is necessary to repeat the test, with further extended dilution, i.e. 1:1024,1:2024, and so on.
It is done to protect against Rh sensitization.
It is usually repeated several times during pregnancy (at 32, 36, and 38 weeks). A titer less than 1:16 may not pose any problem for the baby. In any test higher than 1:64, an intrauterine exchange transfusion may be suggested.

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