Cryoglobulins are abnormal proteins. This article describes the blood test used to check for them.

When the body temperature is lower than 98.6 degrees F (37 degrees C), cryoglobulins no longer float in the blood. Instead, they separate out, forming clusters that can block small blood vessels, especially in the face and hands.

The blood will be taken from a vein, usually on the inside of the elbow or the back of the hand.

The health care provider will clean the area with a germ-killing medicine (antiseptic). Next, an elastic band is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the band to fill with blood.

The health care provider places a needle into the vein. You may feel a tiny stick or pinch. The blood collects into an air-tight container or tube (syringe) attached to the needle. While the blood is being collected, the band is taken off to restore normal blood flow to the area.

After the needle is removed, a cotton ball or bandage is placed over the site to stop any bleeding.

There is no special preparation for this test.

Some people feel discomfort when the needle is inserted. Afterward, there may be some throbbing.

This test is most often done when a person's symptoms suggest a condition that associated with cryoglobulins. Cryoglobulins are associated with several disorders, including those that affect the skin, joints, kidneys, and nervous system.

Normally, there are no cryoglobulins.

A positive test may indicate:

• Hepatitis (especially hepatitis C)
• Infectious mononucleosis
• Leukemia
• Lymphoma
• Macroglobulinemia - primary
• Multiple myeloma
• Rheumatoid arthritis
• Systemic lupus erythematosus

• Nephrotic syndrome

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

There are many specific sub-types of cryoglobulins, and tests may determine the specific type present.

Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.