hematology and oncology
Overview of Platelet Disorders
Diagnosis of Platelet Disorders
Clinical presentation of petechiae and mucosal bleeding Complete blood count (CBC) with platelets, coagulation studies, peripheral blood smear Sometimes bone marrow aspiration Sometimes von Willebrand antigen, platelet-binding activity, and multimer studies Platelet disorders are suspected in patients with petechiae and mucosal bleeding. A CBC with platelet count, coagulation studies, and a peripheral blood smear are obtained. Excessive platelets and thrombocytopenia are diagnosed based on the platelet count. Coagulation studies are normal unless there is a simultaneous coagulopathy. In patients with a normal CBC, platelet count, international normalized ratio (INR), and partial thromboplastin time (PTT), platelet or vessel wall dysfunction is suspected. Suspect platelet or vessel wall dysfunction in patients with petechiae and/or hemorrhage but with normal platelet count and coagulation test results. is important in patients with thrombocytopenia because automated platelet counts sometimes show pseudothrombocytopenia due to platelet clumping caused by the ethylenediaminetetraacetic acid (EDTA) reagent present in some blood collection tubes. Also, schistocytes may be seen, which can indicate valvular hemolysis, Thrombotic Thrombocytopenic Purpura (TTP) (TTP), is often indicated if the smear shows abnormalities other than thrombocytopenia, such as nucleated red blood cells (RBCs) or abnormal or immature white blood cells (WBCs). Bone marrow aspiration reveals the number and appearance of megakaryocytes and is the definitive test for many disorders that cause bone marrow failure. If the bone marrow is normal but the spleen is enlarged, increased Thrombocytopenia Due to Splenic Sequestration is the likely cause of thrombocytopenia. If the bone marrow is normal and the spleen is not enlarged, excess platelet destruction is the likely cause. However, normal number and appearance of megakaryocytes does not always indicate normal platelet production. For example, in many patients with Immune Thrombocytopenia (ITP) (ITP), platelet production may be decreased despite the normal appearance and increased number of megakaryocytes. In fact, bone marrow examination is rarely required in patients who present with The immature platelet fraction in peripheral blood is sometimes a useful measure in patients with thrombocytopenia, since it is elevated when the bone marrow is producing platelets and not increased when marrow platelet production is reduced, similar to the reticulocyte count in anemia. Measurement of antiplatelet antibodies may be clinically useful in some patients to distinguish ITP from other causes of thrombocytopenia Diagnosis reference . HIV testing is done in patients with or at risk of HIV infection, hepatitis B or C infection, or HIV and hepatitis coinfection. In patients with platelet dysfunction, a drug cause is suspected if symptoms began only after the patient started taking a potentially causative drug (eg, ticarcillin,prasugrel,clopidogrel,ticagrelor,abciximab). Platelet dysfunction caused by drugs may be severe, but specialized tests are rarely needed. A hereditary cause is suspected if there is a lifelong history of easy bruising; bleeding after tooth extractions, surgery, childbirth, or circumcision; or heavy menstruation. In the case of a suspected hereditary cause,von Willebrand factor(VWF) antigen and VWF activity studies are routinely done. In patients with suspected hereditary dysfunction, platelet aggregation tests may identify a defect in how the platelet responds to various platelet agonists (adenosinediphosphate [ADP], collagen,thrombin) and thereby demonstrate the type of platelet defect. Platelet dysfunction caused by systemic disorders is typically mild and of minor clinical importance. In these patients, the causative systemic disorder is the clinical concern, and hematologic tests are unnecessary. 1.Al-Samkari H, Rosovsky RP, Karp Leaf RS: A modern reassessment of glycoprotein-specific direct platelet autoantibody testing in immune thrombocytopenia.Blood Adv4(1):9–18, 2020. doi: 10.1182/bloodadvances.2019000868 