A positive antinuclear antibody test predicts for a poor response to initial steroid therapy in adults with idiopathic thrombocytopenic purpura.

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 = 0.006). The difference in mean platelet count between positive and negative ANA-tested patients remained significant after adjusting for sex, age, and ESR (P = 0.001). Also, patients with a positive ANA were 6.25 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.