Quantitative immunoglobulins - nephelometry

Definition

Nephelometry is a laboratory technique that uses a specialized instrument to quickly and accurately measure IgM, IgG, and IgA immunoglobulins in a blood sample.

How the test is performed

Blood is drawn from a veinon the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and 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.

A needle is inserted into the vein, and the blood is collected in an airtight vial or a syringe. During the procedure, the band is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

For an infant or young child:

The area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding.

How to prepare for the test

You may be asked to fast for 4 hours before the test.

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

The test provides a rapid and accurate measurement of the amounts of immunoglobulins M, G, and A. (Immunoglobulin D has no known clinical significance, and IgE must be measured by more sensitive techniques such as radioimmunoassay or enzyme-linked immunoassay.)

Normal Values

• IgG: 560 to 1800 mg/dL
• IgM: 45 to 250 mg/dL
• IgA: 100 to 400 mg/dL

What abnormal results mean

Increased levels of IgG may indicate the following:

• Chronic infection
• Hyperimmunization
• IgG multiple myeloma
• Liver disease
• Rheumatoid arthritis
• Rheumatic fever

• Agammaglobulinemia (very rare)
• Amyloidosis
• Leukemia
• Preeclampsia

• Infectious mononucleosis
• Lymphosarcoma
• Macroglobulinemia
• Rheumatoid arthritis

• Agammaglobulinemia (very rare)
• Amyloidosis
• Leukemia

• Chronic infections, especially involving the gastrointestinal tract
• Inflammatory bowel disease
• Rheumatic fever

• Agammaglobulinemia (very rare)
• Protein-losing gastroenteropathy
• Hereditary IgA deficiency

What the risks are

• 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

Special considerations

Nephelometry determines the total amount of each immunoglobulin but cannot distinguish monoclonal antibodies. Other tests such as immunoelectrophoresis or immunofixation can be used to make these distinctions.

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.

Illustrations

Blood test