Review Question - QID 108125

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Thrombotic Thrombocytopenic Purpura (TTP) Evaluation Peripheral blood smear QID: 108125 (M1.HE.16.4697)

QID 108125 (Type "108125" in App Search)

A 23-year-old female presents to the emergency department stating that she is “not thinking clearly.” Her vital signs are as follows: T 101.2 F, HR 110, BP 104/72, RR 18, SpO2 98% RA. Her physical exam is notable for the following findings in her oropharynx (Figure A). Complete blood count reveals: WBC 11.7 x 10^9/L, Hemoglobin 7.3 g/dL, Platelets 54 x10^9/L. Basic metabolic panel reveals: Sodium 137 mEq/L, Potassium 5.2 mEq/L, Chloride 100 mEq/L, Bicarbonate 22 mEq/L, Creatinine 2.78 mEq/L. Which of the following additional findings would you expect in this patient?

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Schistocytes, Elevated INR, Low fibrinogen, Elevated LDH

24%

15/63

Schistocytes, Elevated LDH, Elevated indirect bilirubin, Negative Coombs’ test

48%

30/63

Sickled cells, Elevated LDH, Negative Coombs’ test

1/63

Burr cells, Normal LDH, Prolonged bleeding time

3/63

Bite cells, Elevated LDH, Elevated indirect bilirubin

1/63

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This patient's clinical presentation is consistent with thrombotic thrombocytopenic purpura, which is due to a defective, inhibited, or deficient ADAMTS13 enzyme.

Thrombotic thrombocytopenic purpura (TTP) is classically characterized by the pentad of fever, neurological changes, acute renal failure, microangiopathic hemolytic anemia, and thrombocytopenia. Laboratory findings of hemolytic anemia include an elevated LDH and elevated indirect bilirubin. Peripheral blood smear will reveal schistocytes, fragmented red blood cells caused by passage through thrombosed small vessels. Coombs’ test is negative in TTP, as autoantibodies against RBCs are not formed in the pathogenesis of this disease.

Dhaliwal et al. review the differential diagnosis of hemolytic anemia. Immune-mediated hemolytic anemia is due to antibodies to red blood cell antigens. Microangiopathic hemolytic anemias are caused by mechanical shearing of red blood cells in the circulation. Hereditary causes of hemolytic anemia include enzymopathies (e.g. G6PD deficiency), membranopathies (e.g. hereditary spherocytosis), and hemoglobinopathies (e.g. sickle cell disease). Infections that causes hemolytic anemia include malaria and babesiosis.

Burns et al. studied the presence of schistocytes in the diagnosis of TTP. They found that schistocytes were found in 100% of peripheral blood smears of TTP patients and 58% of normal individuals. However, normal patients always had a schistocyte percentage of less than 0.5% of the red blood cell population. They concluded that an initial schistocyte count of greater than 1% strongly suggests a diagnosis of TTP.

Figure A demonstrates numerous petechiae of the soft palate.

Incorrect Answers:
Answer 1: These findings would be consistent with disseminated intravascular coagulation.
Answer 3: Hemolysis occurs in sickle cell disease, but autoantibodies are not formed in the pathogenesis of this disease and thrombocytopenia is not commonly seen.
Answer 4: Burr cells are commonly seen in uremia, but anemia associated with renal disease is primarily due to erythropoietin deficiency and not hemolysis.
Answer 5: Bite cells are commonly seen in G6PD deficiency, which is inconsistent with this patient’s presentation.