Which additional finding would be inconsistent with a diagnosis of IgA vasculitis in a child with a purpuric rash?

In the context of a diagnosis of IgA vasculitis, also known as Henoch-Schönlein purpura (HSP), several clinical features are typically present. The condition is characterized by a purpuric rash, usually on the buttocks and legs, along with abdominal pain, arthritis, and renal involvement that may manifest as hematuria and proteinuria.

A low platelet count would be inconsistent with IgA vasculitis because this condition does not typically involve thrombocytopenia. Patients with HSP usually have normal platelet counts, as the pathophysiology of the disease does not imply increased consumption or destruction of platelets.

In contrast, a high white blood cell count, elevated creatinine, and the presence of hematuria can all be associated with IgA vasculitis. A high white blood cell count may reflect an inflammatory response, while elevated creatinine indicates potential renal involvement, often seen in these patients. Hematuria can occur due to renal involvement associated with IgA deposition in the glomeruli. Thus, the presence of these findings aligns with the typical clinical picture of IgA vasculitis, further reinforcing the notion that a low platelet count is the outlier in this scenario.