What is your approach to an infant (<12 mo) with new onset petechiae and thrombocytopenia, with labs consistent with ITP?

In an older (1-6 year old) child with apparent ITP, less work up might be needed. While many tests are possible, in this case, labs consistent with ITP, I would interpret as including a CBC otherwise normal for age without blasts on a smear (if this is not true, the differential is much wider). If it is true, the other etiologies to consider include an underlying immune deficiency and an inherited thrombocytopenia. In addition, viral infections e.g., CMV need to be evaluated. In addition, there is some data that these patients, if they have ITP, do worse than older children. Underlying immune deficiency can be explored with immunoglobulin levels and a test panel e.g., from Invitae. Inherited thrombocytopenias are more difficult because pane...