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Self-Assessment Questions

Internal Medicine

Heparin-Induced Thrombocytopenia: Review Questions

David McAdams, MD, MS

Dr. McAdams is an Assistant Professor of Medicine, Division of General Internal Medicine, University of Pittsburgh Medical Center, Pittsburgh, PA.

Choose the single best answer for each question.

1. What is the incidence of immune-mediated heparin-induced thrombocytopenia (HIT type II) in patients exposed to heparin for more than 4 days?
  1. 10%–20%
  2. 5%–10%
  3. 3%–5%
  4. 0.3%–3%
  5. 0.05%–0.1%
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2. What is the median platelet count nadir in HIT type II?

  1. 100 x 103/mm3
  2. 80 x 103/mm3
  3. 60 x 103/mm3
  4. 20 x 103/mm3
  5. 10 x 103/mm3
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3. Which of the following manifestations of HIT leads to the most frequent complications in HIT?

  1. Arterial thrombosis
  2. Venous thrombosis
  3. Thrombocytopenia
  4. Heparin-induced skin lesions
  5. Acute systemic reactions (ie, fevers, chills, rigors, tachycardia, hypertension)
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Questions 4 and 5 refer to the following case study.

A 45-year-old man with diabetes, chronic atrial fibrillation, and chronic renal insufficiency is admitted to the hospital with 3 days of cough and fever. Physical examination demonstrates right lung base rales and consolidation. Routine laboratory tests demonstrate the following: serum electrolytes, normal levels; blood urea nitrogen, 36 mg/dL; serum creatinine, 3.1 mg/dL (patient’s baseline is 2.6 mg/dL); leukocyte count, 14.5 x 103/mm3; platelet count, 170 x 103/mm3; and international normalized ratio, 1.2. A chest radiograph shows a right lower lobe infiltrate, and a diagnosis of pneumonia is made. The patient is started on ceftriaxone and azithromycin. He is placed on unfractionated heparin and warfarin for treatment of his atrial fibrillation. On hospital day 5, the patient complains of right calf pain and swelling. Duplex ultrasonography demonstrates venous thrombosis in the right lower extremity. Platelet count is now 54 x 103/mm3. HIT is suspected.

4. Which of the following statements about the diagnosis of HIT is CORRECT?
  1. Diagnosis of HIT is most reliably made when both clinical and pathologic criteria are met
  2. Diagnostic testing for HIT has a quick turnaround time and is almost always immediately available at most medical centers
  3. Enzyme immunoassays (ie, detection of antibodies against the heparin/PF4 complexes that contribute to HIT) are considered the “gold standard” in the diagnosis of HIT
  4. The concordance between activation assays (those in which heparin “activates” normal donor platelets in the presence on the patient’s serum) and enzyme immunoassays is approximately 100%
  5. The advantage of the 14C-serotonin release assay is its low cost
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5. In addition to the immediate cessation of all unfractionated heparin products, the next appropriate step in the treatment of HIT in this patient is the addition of which one of the following?

  1. Low-molecular-weight heparin (LMWH)
  2. Aspirin
  3. Lepirudin
  4. Argatroban
  5. Ancrod
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