AB - Adult idiopathic thrombocytopenic purpura (ITP) is an acquired autoimmune disease that may be associated with other autoimmune disorders and a positive antinuclear antibody (ANA). This pilot study aimed to determine the clinical significance of a positive ANA test on the presentation and response to steroids. The medical records of 46 patients aged 15 years or older who were diagnosed with ITP at King Abdullah University Hospital from January, 2004 to December, 2006 were retrospectively analyzed. ANA results were available for 41 patients, and only 10 patients had a positive test. The study showed no association between the ANA and any of the patients' characteristics at presentation. This included the age, sex, presence of autoimmune diseases, a family history of autoimmune diseases, platelet count, hemoglobin level, and erythrocyte sedimentation rate (ESR). It is interesting to note that the mean platelet count after 2 weeks of steroids was 99,323 per cu/ml in patients with a negative ANA, and 32,800 per cu/ml in those with a positive ANA (P = ). The difference in mean platelet count between positive and negative ANA-tested patients remained significant after adjusting for sex, age, and ESR (P = ). Also, patients with a positive ANA were times more likely of not achieving a complete response defined as a platelet count of 100,000 per cu/ml or more for a minimum of 3 months after discontinuation of therapy. In conclusion, the ANA test could be a useful screening test that predicts initial response to steroid therapy. Patients who test positive are expected to have lower response and should be monitored closely.
Anti-double stranded DNA (anti-dsDNA) antibodies are highly associated with SLE. They are a very specific marker for the disease, with some studies quoting nearly 100%.  Data on sensitivity ranges from 25–85%. Anti-dsDNA antibody levels, known as titres, correlate with disease activity in SLE; high levels indicate more active lupus. The presence of anti-dsDNA antibodies is also linked with lupus nephritis and there is evidence they are the cause. Some anti-dsDNA antibodies are cross reactive with other antigens found on the glomerular basement membrane (GBM) of the kidney, such as heparan sulphate , collagen IV, fibronectin and laminin . Binding to these antigens within the kidney could cause inflammation and complement fixation , resulting in kidney damage. Presence of high DNA-binding and low C3 levels have been shown to have extremely high predictive value (94%) for the diagnosis of SLE.  It is also possible that the anti-dsDNA antibodies are internalised by cells when they bind membrane antigens and then are displayed on the cell surface. This could promote inflammatory responses by T-cells within the kidney. It is important to note that not all anti-dsDNA antibodies are associated with lupus nephritis and that other factors can cause this symptom in their absence. The antigen of anti-dsDNA antibodies is double stranded DNA .