The cold agglutinin titer is a diagnostic test for cold agglutinin disease (CAD).

High levels of cold agglutinins, which are autoantibodies mostly of the IgM type, can bind to and induce the agglutination (or clumping) and destruction of red blood cells (RBCs) when exposed to cold temperatures. This causes hemolytic anemia.

What the cold agglutinin titer measures

The cold agglutinin (CA) titer refers to the number of dilutions after which the antibodies can still cause the agglutination of RBCs. It is a measure of autoantibody concentration and RBC-binding strength.

Cold agglutinins are present at very low concentrations in all people. They may also be detected in individuals with pneumonia. CA titers exceeding 1:64 dilution can be used as an indication of CAD.

How the CA titer is determined

First, a blood sample is processed to obtain the plasma (the liquid portion of blood) by separating it from the blood cells. The plasma is then serially diluted and an equal amount of RBC solution is added to all the dilutions and incubated overnight at 4 C. These RBCs may be derived from the patient’s blood or obtained from commercial sources.

The sample is analyzed immediately for RBC clumping either by the eye or under a microscope. This is done quickly and at low temperatures because the binding of the antibody to the RBCs is temperature-dependent.

After reading the results, the samples are kept at 37 C for a couple of hours. If the agglutination was caused by CA antibodies, it dissolves after this period.

Interpretation of the CA titer test results

The CA titer test results can be interpreted as follows:

  • If CA antibodies are not present, RBCs will not agglutinate at either temperature (4 C or 37 C).
  • ¬†If CA antibodies are present, RBCs will clump at the cold temperature but not at the higher temperature.

The titer is the highest dilution of the plasma at which agglutination of RBCs occurs in cold temperatures. A CA titer greater than or equal to 1:64 is considered a positive result for CAD. Most experts consider a titer above 1:512 to be clinically significant. Sometimes, a CA titer can be as high as 1:2048.

 

Last updated: August 13, 2019

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