What laboratory test is most helpful in confirming a diagnosis of IgA vasculitis?

In diagnosing IgA vasculitis, also known as Henoch-Schönlein purpura (HSP), a complete blood count (CBC) with differential is a valuable tool. This test can provide insight into the overall blood health and detect any abnormalities that might support the diagnosis. Common findings in IgA vasculitis include mild leukocytosis and increased eosinophil counts, along with the possible presence of thrombocytosis.

While urinalysis can show signs of kidney involvement, such as hematuria or proteinuria, it is not definitive for confirming IgA vasculitis, as these findings can be seen in various other conditions as well. Blood cultures are primarily used to identify bacterial infections, which are not directly related to IgA vasculitis. Liver function tests assess liver health and are not relevant to the diagnosis of this condition, making them less useful in this specific context.

Thus, the CBC with differential stands out as the most helpful laboratory test for confirming IgA vasculitis due to its ability to reveal hematological changes that can occur in this disease.