Final answer:
People with undiagnosed thrombocytopenia need a platelet transfusion when presenting with symptoms such as petechiae, severe bruising, joint swelling, and hematomas.
Step-by-step explanation:
People with undiagnosed thrombocytopenia need a platelet transfusion when presenting with multiple petechiae on skin or gums, severe bruising, joint swelling, and hematomas. Thrombocytopenia is a condition characterized by an insufficient number of platelets, which can result in abnormal bleeding due to the inability of blood to form clots. Platelet transfusion can help increase the number of platelets in the blood, allowing for proper clotting.