Thermal Amplitude Test

A thermal amplitude test is one of the laboratory tests that can be used to diagnose cold agglutinin disease (CAD).

In this rare disease, the immune system generates autoantibodies — antibodies that attack the body’s own cells and tissues — against red blood cells in cold temperatures. These autoantibodies, called agglutinins, cause red blood cells to clump and be destructed by the immune system in cold temperatures, causing anemia and the other symptoms of CAD.

What is a thermal amplitude test?

The thermal amplitude test measures the temperatures at which red blood cells clump together when combined with a blood sample from a CAD patient. This clumping is visible both under a microscope and with the naked eye.

How is a thermal amplitude test performed?

To perform a thermal amplitude test, a blood sample is collected from the patient. This can be done at a clinic or hospital. The blood is separated into its liquid and cell components. The liquid portion, also called plasma, contains the antibodies that are present in the person’s blood.

The plasma is then added to normal blood samples on a slide or card, and the mixture is kept at different temperatures, from normal body temperature (98.6 degrees Fahrenheit) to about 40 F. After incubation, the card or slide is examined by eye or under a microscope, and checked for agglutination, or clumping of the blood cells.

How the thermal amplitude test helps diagnose CAD

Normal plasma should not cause clumping during the thermal amplitude test. The plasma of people with CAD will cause clumping of blood cells at temperatures below 98.6 degrees Fahrenheit. However, the closer to body temperature clumping occurs, the more harmful the patient’s cold agglutinins are.

For people whose thermal amplitude is very high — that is, clumping occurs at high temperatures — special precautions may need to be taken to prevent the blood from clumping as it is collected for the test. Samples may need to be kept at body temperature, or slightly higher, to prevent blood samples from degrading following collection.

What happens next?

After the results of the thermal amplitude test, the physician will meet with the patient and explain the results of this and other tests. After explaining the diagnosis, the physician will discuss potential treatment options.


Last updated: Aug. 19, 2019


Cold Agglutinin Disease News is strictly a news and information website about the disease. It does not provide medical advice, diagnosis, or treatment. This content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified healthcare providers with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website.