Final answer:
Thrombocytopenia is caused by an insufficient number of platelets, leading to increased bleeding risks; it can be due to decreased production or an autoimmune process.
Step-by-step explanation:
The nurse should explain to the patient diagnosed with thrombocytopenia that this condition is characterized by an insufficient number of platelets in the blood, which contributes to a reduced ability for the blood to form clots. As such, patients can experience excessive bleeding even from minor injuries. Thrombocytopenia can have several causes, including the decreased production of platelets within the bone marrow or an increased destruction of platelets, which may occur due to an autoimmune process wherein the body's immune system mistakenly attacks the platelets as if they were foreign substances.