Beta₂-Microglobulin Test

Definition

Beta₂-microglobulin is a protein found on the surface of many cells. Testing is done primarily when evaluating a person for certain kinds of cancer affecting white blood cells including chronic lymphocytic leukemia, non-Hodgkin's lymphoma, and multiple myeloma or kidney disease.

Purpose

Beta₂-microglobulin is plentiful on the surface of white blood cells. Increased production or destruction of these cells causes Beta₂-microglobulin levels in the blood to increase. This increase is seen in people with cancers involving white blood cells, but it is particularly meaningful in people newly diagnosed with multiple myeloma. Multiple myeloma is a malignancy (cancer) of a certain kind of white blood cell, called a plasma cell. At the time of diagnosis, the Beta₂-microglobulin levels reflect how advanced the disease is and the likely prognosis for that person.

When kidney disease is suspected, comparing blood and urine levels helps identify where the kidney is damaged. Beta₂-microglobulin normally is filtered out of the blood by the kidney's glomeruli (a round mass of capillary loops leading to each kidney tubule), only to be partially reabsorbed back into the blood when it reaches the kidney's tubules. In glomerular kidney disease, the glomeruli can't filter it out of the blood, so levels increase in the blood and decrease in the urine. In tubular kidney disease, the tubules can't reabsorb it back into the blood, so urine levels rise and blood levels fall. After a kidney transplant, increased blood levels may be an early sign of rejection.

Increased urinary levels are found in people with kidney damage caused by high exposure to the heavy metals cadmium and mercury. Periodic testing of workers exposed to these metals helps to detect beginning kidney damage.

Beta₂-microglobulin levels also rise during infection with some viruses, including cytomegalovirus and human immunodeficiency virus (HIV). Studies show that as HIV disease advances, beta₂-microglobulin levels rise.

Description

Testing methods vary, but most involve adding the person's serum—the yellow, liquid part of blood—or urine to one or more substances that bind to beta₂microglobulin in the serum or urine. The amount of the substance(s) bound to beta₂-microglobulin is measured and the original amount of beta₂-microglobulin is determined.

The test is covered by insurance when medically necessary. Results are usually available the next day.

Preparation

The blood test requires 5 mL of blood. A healthcare worker ties a tourniquet on the person's upper arm, locates a vein in the inner elbow region, and inserts a needle into that vein. Vacuum action draws the blood through the needle into an attached tube. Collection of the sample takes only a few minutes.

Urine may be a single collection or collected throughout a 24-hour time period. The urine should be refrigerated until it is brought to the laboratory and must not become acidic.

Aftercare

Discomfort or bruising may occur at the puncture site or the person may feel dizzy or faint. Pressure to the puncture site until the bleeding stops reduces bruising. Warm packs on the puncture site relieve discomfort.

Normal results

• Serum: less than or equ to 2.7 g/ml
• Urine: less than 1 mg 24 hours 0-160 g/L

Abnormal results

The meaning of an abnormal result varies with the clinical condition of the person tested. In a person with multiple myeloma, a higher level means a poorer prognosis than a lower level. In a person with kidney disease, an increased blood level means the problem is tubular, not glomerular. In a kidney transplant patient, an increase may be a sign of rejection, toxic amounts of antirejection medication, or a viral infection. An increased level in a worker exposed to cadmium or mercury may signal beginning kidney damage and in a person with HIV, advancing disease.

Resources

BOOKS

Lehmann, Craig A. Saunders Manual of Clinical Laboratory Science. Philadelphia: W. B. Saunders Co., 1998.

KEY TERMS

Beta₂-microglobulin— A protein found on the surface of many cells, particularly white blood cells.

Chronic lymphocytic leukemia— A cancer of the blood cells characterized by large numbers of cancerous, mature white blood cells and enlarged lymph nodes.

Glomerular kidney disease— Disease of the kidney that affects the glomeruli, the part of the kidney that filters certain substances out of the blood.

Muliple myeloma— A malignancy (cancer) of a certain kind of white blood cell, called a plasma cell.

Non-Hodgkin's lymphoma— Cancer that originates in the lymphatic system and typically spreads throughout the body.

Tubular kidney disease— Disease of the kidney that affect the tubules, the part of the kidney that allows certain substances to be reabsorbed back into the blood.