Indications:
The presence of anti-dsDNA antibodies is observed that in case of lupus.
In contrast, anti-DNA antibodies denatured, less specific, are found in several autoimmune diseases, including rheumatoid arthritis, scleroderma and also hepatitis.
Principle:
The Farr assay consists in bringing the patient’s serum with the DNA labeled with carbon 14. It then precipitated proteins by ammonium sulfate and measuring the radioactivity of the pellet.
Sampling 5 to 10 mL of venous blood in a dry tube.
Laboratories with the necessary reagents (radioisotopes) to perform this examination are few.
A determination is also possible by indirect immunofluorescence or ELISA technology.
Results:
The results are provided in International Units (IU) or a percentage of a control sample.
It s are considered positive if their rate exceeds 20%.
The higher the rate, the higher the risk is of poly-vicérale, renal in particular.
In contrast, a low rate only sign a cutaneous lupus reached.
In case of drug-induced lupus, there is no modification of the native DNA levels.
Monitoring the rate is also an important part of controlling the therapeutic efficiency and scalability of the disease.
Cost:
B40 or B70.
Practical advice:
Drugs can alter the native DNA levels: beta blockers, procainamide, hydantoin, D penicillamine.