A 24-year-old woman at 10 weeks gestation comes to the office for evaluation of thrombocytopenia. She was found to have a platelet count of 90,000/mm³ at her initial prenatal visit last week. The patient has no known history of a blood disorder; she had episodes of epistaxis during childhood but none since and has never had other bleeding issues. Prior to her pregnancy, her menses occurred monthly and lasted 4-5 days with light vaginal bleeding. The patient has no other medical conditions and takes no medications. She drank alcohol occasionally but stopped after a positive home pregnancy test. There is no significant family history of blood disorders or cancer. Vital signs are within normal limits. Physical examination shows no enlarged lymph nodes or hepatosplenomegaly. The remainder of the physical examination is unremarkable. Repeat platelet count is 98,000/mm³. Peripheral blood smear is shown in the exhibit. Which of the following is the most likely diagnosis?

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11ec25c8_d42f_c531_bc81_93cf42d95f42_MD0003_00 This patient has mild thrombocytopenia with no associated symptoms (eg, bruising, mucocutaneous bleeding), no personal/family history of bleeding diathesis, and no abnormal physical examination findings. Peripheral blood smear reveals large clumps of platelets. This presentation raises suspicion for pseudothrombocytopenia. Pseudothrombocytopenia is a laboratory error caused by platelet aggregation in vitro. Most cases are due to incompletely mixed blood samples or the presence of serum antibodies to ethylenediaminetetraacetic acid (EDTA), an anticoagulant used in hematologic testing. The error is generally identified when a patient with mild thrombocytopenia has peripheral blood smear evidence of large clumps of platelets. Drawing blood samples in tubes with a non-EDTA anticoagulant (eg, heparin, sodium citrate) normalizes the automated platelet count and confirms the diagnosis. Because patients with pseudothrombocytopenia do not have true thrombocytopenia, they do not require intervention or monitoring. (Choice A) Gestational thrombocytopenia is the most common cause of thrombocytopenia during pregnancy. It is generally mild and does not cause maternal or fetal morbidity. However, gestational thrombocytopenia usually arises in the second half of the pregnancy (not at 10 weeks), and peripheral blood smear would reveal a paucity of platelets (not platelet clumping). (Choice B) Glanzmann thrombasthenia is an autosomal recessive disorder associated with impaired platelet aggregation. Patients generally have a history of mucocutaneous bleeding, normal platelet counts, and no platelet clumping on peripheral blood smear. (Choice C) Idiopathic thrombocytopenic purpura, which is approximately tenfold more common in pregnant women than in the general population, usually presents with mild thrombocytopenia. Patients are often asymptomatic and have no history of bleeding disorder. However, peripheral blood smear would show a paucity of platelets, not platelet clumping. (Choice E) Vitamin B₁₂ deficiency can occasionally cause mild thrombocytopenia and leukopenia. However, peripheral blood smear usually shows hypersegmented neutrophils and macrocytic anemia; platelet clumping would not be seen. macrocytic anemia (Choice F) Von Willebrand disease is the most common inherited bleeding disorder. It is marked by a defect in platelet aggregation due to a deficiency of von Willebrand factor. Most cases are asymptomatic, and patients have normal platelet counts and peripheral smears. Educational objective: Pseudothrombocytopenia is a laboratory error characterized by platelet aggregation in vitro. It is generally confirmed when peripheral smear reveals large clumps of platelets. Patients do not require additional evaluation or follow-up and are not at risk for bleeding.

A 24-Year-Old Woman at 10 Weeks Gestation Comes to the Office