Which laboratory test would provide information about the number of megakaryocyte?

Essential thrombocythemia Essential Thrombocythemia Essential thrombocythemia (ET) is a myeloproliferative neoplasm characterized by an increased platelet count, megakaryocytic hyperplasia, and a hemorrhagic or microvascular vasospastic tendency... read more is a myeloproliferative neoplasm Overview of Myeloproliferative Neoplasms Myeloproliferative neoplasms are clonal proliferations of bone marrow stem cells, which can manifest as an increased number of platelets, red blood cells (RBCs), or white blood cells (WBCs)... read more (previously called a myeloproliferative disorder) involving overproduction of platelets because of a clonal abnormality of a hematopoietic stem cell. There is no correlation between the platelet count and risk of thrombosis, but some patients with extreme thrombocytosis (ie, > 1,000,000/mcL [> 1000 × 109/L]) develop bleeding due to loss of high molecular weight von Willebrand factor multimers (acquired type 2B von Willebrand disease Von Willebrand Disease Von Willebrand disease (VWD) is a hereditary quantitative deficiency or functional abnormality of von Willebrand factor (VWF), which causes platelet dysfunction. Bleeding tendency is usually... read more ).

Reactive thrombocytosis Reactive Thrombocytosis (Secondary Thrombocythemia) Reactive thrombocytosis is an elevated platelet count (> 450,000/mcL [> 450,000 × 109/L]) that develops secondary to another disorder. (See also Overview of Myeloproliferative... read more is platelet overproduction in response to another disorder. There are many causes, including acute infection, chronic inflammatory disorders (eg, rheumatoid arthritis Rheumatoid Arthritis (RA) Rheumatoid arthritis is a chronic systemic autoimmune disease that primarily involves the joints. Rheumatoid arthritis causes damage mediated by cytokines, chemokines, and metalloproteases.... read more

Tuberculosis (TB) Tuberculosis is a chronic, progressive mycobacterial infection, often with an asymptomatic latent period following initial infection. Tuberculosis most commonly affects the lungs. Symptoms include... read more

Sarcoidosis Sarcoidosis is an inflammatory disorder resulting in noncaseating granulomas in one or more organs and tissues; etiology is unknown. The lungs and lymphatic system are most often affected, but... read more

• Decreased platelet production

• Increased splenic sequestration of platelets with normal platelet survival

• Increased platelet destruction or consumption (both immunologic and nonimmunologic causes)

• Dilution of platelets

Overall, the most common specific causes of thrombocytopenia include

• Drugs that cause immune-mediated platelet destruction (commonly, heparin, trimethoprim/sulfamethoxazole, rarely quinine [cocktail purpura] or abciximab), and rarely vaccinations (eg, influenza, shingles, measles, mumps, and rubella, A COVID-19)

• Drugs that cause dose-dependent bone marrow suppression (eg, chemotherapeutic agents, ethanol)

• Systemic infection

Symptoms and Signs of Platelet Disorders

Platelet disorders result in a typical pattern of bleeding:

• Multiple petechiae in the skin (typically most evident on the lower legs)

• Scattered small ecchymoses at sites of minor trauma or venipuncture sites

• Mucosal bleeding (oropharyngeal, nasal, gastrointestinal, genitourinary)

• Excessive bleeding after surgery

• Extensive menstrual bleeding

Peripheral smear examination 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 Thrombotic Thrombocytopenic Purpura (TTP) Thrombotic thrombocytopenic purpura (TTP) is an acute, fulminant disorder characterized by thrombocytopenia and microangiopathic hemolytic anemia. Other manifestations may include alterations... read more

Hemolytic-Uremic Syndrome (HUS) Hemolytic-uremic syndrome (HUS) is an acute, fulminant disorder characterized by thrombocytopenia, microangiopathic hemolytic anemia, and acute kidney injury. HUS usually occurs in children... read more

Peripheral Blood Findings in Thrombocytopenic Disorders

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.

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 (adenosine diphosphate [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 Adv 4(1):9–18, 2020. doi: 10.1182/bloodadvances.2019000868