Anti-Doublestranded Dna Antibodies

About two-thirds of patients with active systemic lupus erythematosus (SLE) have measurable levels of auto­antibodies to doublestranded (native) deoxyribonucleic acid (known as anti-ds-DNA). These antibodies are rarely detected in patients with other connective tissue diseases.

The anti-ds-DNA antibody test measures and differentiates these antibody levels in a serum sample, using radioimmunoassay, agglutination, complement fixation, or immunoelectrophoresis. If anti-ds-DNA antibodies are present, they combine with native DNA and form complexes that are too large to pass through a membrane filter. The test counts these oversized complexes.

Purpose

• To confirm a diagnosis of SLE
• To monitor the SLE patient's response to therapy and determine his prognosis.

Patient Preparation

• Explain to the patient that this test helps diagnose and determine the appropriate therapy for SLE.
• Advise the patient that he needn't restrict food or fluids.
• Tell him that the test requires a blood sample and who will perform the venipuncture and when.
• Reassure him that although he may experience transient discomfort from the needle puncture and the tourniquet, collecting the sample usually takes less than 3 minutes.
• Ask the patient if he has had a recent radioactive test; if so, note this on the laboratory slip.

Procedure And Posttest Care

• Perform a venipuncture, and collect the sample in a 7-ml red-top tube. (Some laboratories may specify a lavender-or gray-top tube.)
• If a hematoma develops at the venipuncture site, apply warm soaks.

Precautions

• Handle the sample gently to prevent hemolysis.

Reference values

An anti-ds-DNA antibody level less than 25 IU is considered negative for SLE.

Abnormal Findings

Elevated anti-ds-DNA antibody levels may indicate SLE. Values of 25 to 30 IU are considered borderline positive. Values of 31 to 200 IU are positive, and those greater than 200 IU are strongly positive.

Depressed anti-ds-DNA antibody levels may follow immunosuppressive therapy, demonstrating effective treatment of SLE.

Interfering Factors

• A radioactive scan performed within I week before collection of a sample
• Hemolysis due to rough handling of the sample