Anti Dsdna In Serum

Introduction

Calf thymus DNA is highly purified under conditions which maintain the antigen in its native state. This antigen is then bound to polystyrene microwells & stabilized for extended shelf life. Diluted patient sera are placed in the microwells & incubated. If anti- dsDNA antibodies are present, they will bind to the antigen in the microwell. The microwells are then washed to remove residual sample & a second incubation with anti-human IgG & IgM conjugated to alkaline phosphatase is carried out. The conjugate will bind immunologically to the anti- dsDNA IgG and/or IgM portion of the bound antigen- antibody complex, forming a 'sandwich' consisting of:
Conjugate (Enzyme-labeled Anti-human IgG & IgM)
Human anti- dsDNA ( IgG and/or IgM)
Well Coated with dsDNA
Unbound conjugate is removed in the subsequent washing step. Enzyme substrate is then added to the microwell & if bound conjugate is present, the colorless substrate (p-nitrophenyl phosphate), will be hydrolyzed to form a yellow end product, ( p-nitrophenol). The reaction is then stopped & the color fixed. The intensity of the color is measured photometrically at 405 nm & is proportional to the concentration of anti- dsDNA present in the patient sample.

This test is intended for the evaluation of sera for the presence of IgG & IgM antibodies to double-stranded (ds) DNA. In addition this test may be used to follow the level of antibodies to dsDNA in individual patients during the treatment & remission of SLE. Antibodies to dsDNA correlated with renal disease in SLE.
Antibodies to dsDna occur in at least 60-70% of SLE patients & there is considerable evidence to implicate immune complexes containing anti-DNA & DNA in the pathogenesis of SLE. The presence or absence of anti- dsDNA antibodies should not be used as the sole criterion for the diagnosis of SLE.
Low levels of anti- dsDNA antibodies may occur in other connective tissue diseases (i.e. 0-5% of patients with rheumatoid arthritis) & may occur at a very low frequency (2-3%) in individuals without any symptoms of connective tissue disease. It has also been reported that the appearance of anti- dsDNA in patients with connective tissue disease can occur prior to the development of the complete clinical pattern.

Serum is separated from the clot & refrigerated, 2-8 degrees C for short term storage or stored frozen, -20 degrees C, for long term storage. Avoid freeze-thaw cycles.CAUTION: Serum samples should not be heat inactivated, as this may cause false positive results.
No special patient preparation required.

< 100 IU/mL: negative for antibodies to dsDNA.
100-300 IU/mL: borderline for antibodies to dsDNA. Possible SLE or other connective tissue disease ( CTD). Other testing is required for differential diagnosis. See limitations & clinical indications.
300-800 IU/mL: Moderately positive for antibodies to dsDNA. Probable SLE, however other CTD'S cannot be ruled out by this result alone. Other testing is required for differential diagnosis. See limitations & clinical indications.
> 800 IU/mL: Highly positive for antibodies to dsDNA. Virtually diagnostic for SLE.

Henry, John Bernard, Clinical Diagnosis and Management by Laboratory Methods, W. B. Saunders Co., Philadelphia, 1991. pp 891-892.
The Physicians Guide to Anti-DNA Antibody Testing, Diamedix Corporation, Miami, Aug. 1989. pp 1-6.
Summary of Procedure. DiaMedix Corporation, Maimi, Nov. 1991. pp 1-8.
Medical Knowledge Self Assessment Program (MKSAP) 11, American College of Physicians, Philadelphia 1998

anti-dsDNA in serum