A cold agglutinins test is a specialized blood examination used to detect the presence of certain antibodies that react to lower temperatures. These antibodies, called cold agglutinins, can be found in higher-than-normal levels in people with conditions like atypical pneumonia or a rare type of autoimmune hemolytic anemia. The test is unusual in laboratory medicine because the sample’s integrity is directly threatened by a drop in temperature, which necessitates specific and immediate handling protocols from the moment of collection.
Why Temperature Control is Critical
The necessity for unique handling stems directly from the biological activity of the cold agglutinin antibodies. These are autoantibodies, typically of the IgM class, that mistakenly target and bind to antigens found on the surface of a person’s own red blood cells. The binding, or agglutination, is highly temperature-dependent, showing its strongest reaction at temperatures ranging from 0°C to 4°C.
Agglutination (clumping) can occur at temperatures up to 30°C or 31°C, which is well below the normal body temperature of 37°C. If the sample cools slightly after being drawn, the antibodies quickly bind to the red cells in the tube. This premature binding removes the antibodies from the serum, leading to a false-negative or falsely low result during analysis.
Maintaining the sample at or near body temperature prevents the binding reaction. This ensures that the true concentration of cold agglutinins remains in the serum for accurate testing.
Proper Collection and Initial Processing
The collection process begins with measures to prevent the sample from cooling even before the blood is drawn. The collection tube, typically a plain red-top tube (serum separator tubes are generally unacceptable), must be pre-warmed to body temperature (37°C). This is usually done using a warming pack or a temperature-controlled incubator.
Immediately after the blood is collected, the tube must be placed directly into a portable warming container, such as a thermos with a heat pack or a water bath, to maintain 37°C. This warmth allows the blood to clot correctly without the cold agglutinins binding to the red cells. The tube is kept warm until the clotting process is complete, which can take approximately 30 minutes to an hour.
The next step is the rapid separation of the serum from the clotted red blood cells, which must be performed while the sample is still warm. The tube is centrifuged in a warm environment, ideally a centrifuge that is maintained at 37°C. This spinning separates the liquid serum, which contains the cold agglutinins, from the solid cellular components. The separated serum is then transferred into a new plastic vial. Only at this point is the sample protected from the temperature sensitivity of the cold agglutinins for subsequent testing.
Maintaining Sample Integrity During Transport
After the serum has been separated from the cells while warm, transport to the testing facility requires continued attention to temperature. The processed serum sample is typically maintained at refrigeration temperature (2°C to 8°C), which is standard for many laboratory specimens. This refrigeration is only for the serum aliquot that has been separated, not the whole blood.
The physical logistics must ensure the processed serum arrives at the lab within an acceptable stability window, often up to seven days under refrigeration. The sample is usually shipped in insulated containers with cold packs. Because the initial whole blood sample must be kept warm, the transport process only begins after the warm separation of the serum is complete.