How common is a diagnosis of thrombocytopenia in a young female?

Find the cause. It's not a common finding, but if you have it, it is 100%. Thrombocytopenia is something that should never be trifled with; if it gets worse it can cause bad bleeding. In a young woman especially, it can herald lupus. Medications, having one's period, idiopathic thrombocytopenic purpura, allergy to quinine in a cocktail, and a variety of other processes can be the cause.