A 72-year-old woman is evaluated for low platelet count. She is currently being treated for an uncomplicated urinary tract infection with ciprofloxacin. A complete blood count sent as part of the workup showed a platelet count of 12,000/µL. The patient's medical problems include type 2 diabetes mellitus, hypertension, hypercholesterolemia, osteoarthritis, and mild dementia.
Her temperature is 37.2° C (99° F), blood pressure is 130/80 mm Hg, pulse is 84/min, and respirations are 14/min. Physical examination shows no bruises, petechiae, or mucosal bleeding. Cardiopulmonary examination is normal. The abdomen is soft and nontender with no hepatosplenomegaly. The remainder of the examination is within normal limits.
Repeat laboratory results are as follows:

Repeat complete blood count sent in a heparin tube shows a platelet count of 135,000/µL.
Which of the following is the most likely diagnosis?

Question

A 72-year-old woman is evaluated for low platelet count.  She is currently being treated for an uncomplicated urinary tract infection with ciprofloxacin.  A complete blood count sent as part of the workup showed a platelet count of 12,000/µL.  The patient's medical problems include type 2 diabetes mellitus, hypertension, hypercholesterolemia, osteoarthritis, and mild dementia.
Her temperature is 37.2° C (99° F), blood pressure is 130/80 mm Hg, pulse is 84/min, and respirations are 14/min.  Physical examination shows no bruises, petechiae, or mucosal bleeding.  Cardiopulmonary examination is normal.  The abdomen is soft and nontender with no hepatosplenomegaly.  The remainder of the examination is within normal limits.
Repeat laboratory results are as follows:

Repeat complete blood count sent in a heparin tube shows a platelet count of 135,000/µL.
Which of the following is the most likely diagnosis?

Quizplus · Accepted Answer

This patient's clinical presentation suggests pseudothrombocytopenia due to ethylenediaminetetraacetic acid (EDTA)-induced platelet clumping. EDTA is the anticoagulant commonly used in tubes for routine complete blood counts. Pseudothrombocytopenia occurs in about 0.1% of the population. Patients with asymptomatic thrombocytopenia should be evaluated with repeat testing of the platelet count using heparin or sodium citrate as an anticoagulant. Peripheral smear in patients with pseudothrombocytopenia shows platelet clumping that results in an artificially low platelet count. It requires no further follow-up or testing after confirmation of a normal platelet count in a sample using an anticoagulant other than EDTA. (Choice A) Antiphospholipid antibody syndrome is characterized by arterial or venous thrombosis, and/or recurrent pregnancy loss and the presence of an antiphospholipid antibody (eg, lupus anticoagulant). Patients usually have low platelet counts. PTT is prolonged. (Choice B) This patient's platelet count normalized when a heparin-containing tube was used. Heparin-induced thrombocytopenia is characterized by worsening thrombocytopenia (> 50% decrease in platelets from prior measurement) and thrombosis in the setting of recent heparin exposure. (Choice C) Idiopathic thrombocytopenic purpura is presumed when the patient's history (eg, drug exposure), physical examination, complete blood count, and peripheral blood smear examination do not suggest other etiologies for isolated thrombocytopenia. (Choice D) Symptomatic patients with parvovirus B19 infection may present with rash, arthralgias, and edema. Transient aplastic crisis can also be observed. Educational objective: Pseudothrombocytopenia occurs due to ethylenediaminetetraacetic acid (EDTA)-induced platelet clumping and should be suspected in asymptomatic patients with low platelet counts. A repeat platelet count using an anticoagulant other than EDTA that shows normal platelets confirms the diagnosis. __________ References: EDTA-dependent pseudothrombocytopenia: further insights and recommendations for prevention of a clinically threatening artifact. (http://www.ncbi.nlm.nih.gov/pubmed/22868791)

A 72-Year-Old Woman Is Evaluated for Low Platelet Count