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.

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.

There is no special preparation.

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.

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.

• Warm agglutinins: no agglutination in titers at or below 1:80
• Cold agglutinins: no agglutination in titers at or below 1:16

The presence of warm agglutinins may occur with:

• Infections, including brucellosis, rickettsial disease, salmonella infection, and tularemia
• Lymphoma
• Systemic lupus erythematosus
• Use of certain medicines, including methyldopa, penicillin, and quinidine

The presence of cold agglutinins may occur with:

• Infections, especially Mycoplasma pneumonia
• Previous viral, staphylococcal, or malaria infection
• Cancer, including lymphoma and multiple myeloma
• Systemic lupus erythematosus

• Excessive bleeding
• Fainting or feeling light-headed
• Hematoma (blood accumulating under the skin)
• Infection (a slight risk any time the skin is broken)
• Multiple punctures to locate veins

If cold agglutinin disease is suspected, the individual needs to be kept warm.