Go through these in order and stop at the first one that applies. If you are reading this for someone else, answer for them.
Call emergency services for:
Seek urgent medical care for bleeding that is heavy, keeps restarting, or does not stop with firm pressure.
Urgent assessment is also appropriate for blood in urine, black or bloody bowel movements, vomiting or coughing up blood, or menstrual bleeding accompanied by faintness, weakness, or shortness of breath.
These symptoms do not automatically mean ITP has caused internal bleeding, but they require prompt assessment.
Arrange routine medical advice if you develop new unexplained bruises, petechiae, repeated nosebleeds, bleeding gums, or menstrual bleeding that is heavier than usual.
Contact your care team if known ITP symptoms are increasing, a treatment is causing side effects, or you start a new medicine or supplement.
The article also says
Tell your care team in advance about pregnancy, dental treatment, surgery, or an invasive procedure.
You may need a recent platelet count and a plan to limit bleeding.
Every sign above is quoted from the sofidex article on Immune thrombocytopenic purpura. If you are not sure, err upward — it is always reasonable to be checked.