Definition of Febrile/cold agglutinins:

Agglutinins are antibodies that cause the red blood cells to gather together.

• Cold agglutinins are active at cold temperatures.
• Febrile (warm) agglutinins are active at normal body temperature.

This article discusses the blood test used to measures the level of these antibodies in the blood.

How the test is performed:

Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The site is cleaned with germ-killing medicine (antiseptic). The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood.

Next, the health care provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to the needle. (The tube is first warmed to normal body temperature - 98.6 degrees F). The elastic band is removed from your arm.

Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

In infants or young children, a sharp tool called a lancet may be used to puncture the skin and make it bleed. The blood collects into a small glass tube called a pipette, or onto a slide or test strip. A bandage may be placed over the area if there is any bleeding.

The sample is sent to a laboratory.

How to prepare for the test:

There is no special preparation.

How the test will feel:

When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.

Why the test is performed:

This test is done to diagnose certain infections and to determine the cause of hemolytic anemia. Distinguishing between warm and cold agglutinins can help understand why the hemolytic anemia is occurring and directs therapy.