Blood Counts in von Willebrand Disease
In von Willebrand disease, routine blood counts (hemoglobin, white blood cells, and red blood cells) are typically normal, but platelet counts may be intermittently low in Type 2B VWD, and hemoglobin/hematocrit may be reduced due to chronic blood loss from recurrent bleeding episodes. 1
Platelet Count Findings
- Platelet counts are usually normal in most types of VWD (Types 1, 2A, 2M, 2N, and 3) 2
- Intermittent thrombocytopenia is a hallmark feature specifically of Type 2B VWD, occurring because the abnormal VWF spontaneously binds to platelets, leading to their premature clearance from circulation 1
- In Type 2B, platelet counts fluctuate and may normalize between bleeding episodes, making diagnosis challenging if testing occurs during a period of normal counts 1
Red Blood Cell Parameters
- Low hemoglobin and hematocrit are common secondary findings resulting from chronic blood loss due to recurrent mucocutaneous bleeding episodes 1, 2
- Low ferritin levels frequently accompany the anemia, reflecting iron deficiency from ongoing blood loss rather than a primary defect in VWD itself 1
- The severity of anemia correlates with the frequency and severity of bleeding manifestations, particularly in patients with menorrhagia, recurrent epistaxis, or gastrointestinal bleeding 2, 3
White Blood Cell Count
- White blood cell counts remain normal in VWD, as this disorder does not affect leukocyte production or function 2
Coagulation-Related Blood Parameters
- The activated partial thromboplastin time (APTT) may be prolonged, particularly in Type 3 VWD and severe Type 1 VWD, due to secondary Factor VIII deficiency 4
- Bleeding time is characteristically prolonged in most VWD types (except Type 2N), reflecting the platelet adhesion defect, though this test is rarely performed in modern practice 5, 4
- Prothrombin time (PT) and INR remain normal, as VWD does not affect the extrinsic coagulation pathway 2
Important Clinical Pitfalls
- Do not rely on a single normal platelet count to exclude Type 2B VWD—the thrombocytopenia is intermittent and requires repeated testing when clinical suspicion is high 1
- Anemia in VWD patients should prompt evaluation of bleeding severity and consideration for iron supplementation, as the low hemoglobin reflects disease burden rather than a primary hematologic defect 1
- VWF levels are acute phase reactants and may be falsely elevated during stress, inflammation, or recent surgery, potentially masking the diagnosis while blood counts remain the only abnormal finding 1