A 37-year-old woman, gravida 1 para 0, at 25 weeks gestation is evaluated in the antepartum unit due to increasing chest pain. The patient describes a sharp, substernal chest pain that is worse with inspiration and radiates to the right upper quadrant. She has no fever, cough, or rashes. The patient has had no vaginal bleeding or leakage of fluid. She has a twin pregnancy and was admitted for inpatient monitoring for preterm labor 6 days ago. The patient has reduced her activity level because walking increases the contractions, and she has been receiving heparin for venous thromboembolism prophylaxis. Her pregnancy has been otherwise uncomplicated. Temperature is 37.2 C (99 F), blood pressure is 130/86 mm Hg, pulse is 116/min, and respirations are 24/min. Heart rates for both fetuses are 155/min. Lung auscultation shows decreased breath sounds over the right lung base. The uterus is nontender. The lower extremities have bilateral 1+ pitting edema to the knees. Laboratory evaluation is as follows:
| Complete blood count | |
| Hemoglobin | 10.6 g/dL |
| Platelets | 70,000/mm3 |
| Leukocytes | 11,400/mm3 |
| Serum chemistry | |
| Creatinine | 0.6 mg/dL |
| Liver function studies | |
| Alkaline phosphatase | 124 U/L (normal: 25-126) |
| Aspartate aminotransferase (SGOT) | 12 U/L |
| Alanine aminotransferase (SGPT) | 24 U/L |
Which of the following is the most likely diagnosis in this patient?
Heparin-induced thrombocytopenia | |
Clinical features | Heparin exposure ≥5 days & any of the following:
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Diagnosis |
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Treatment |
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This patient most likely has heparin-induced thrombocytopenia (HIT), a life-threatening condition that causes low platelet levels and a paradoxical prothrombotic state. HIT typically occurs 5-10 days after heparin exposure and affects up to 5% of patients. In those who develop the syndrome, heparin forms a complex with a platelet surface protein (platelet factor 4), inducing the immune system to produce HIT antibodies. These antibodies bind to platelet surfaces, leading to:
Thrombocytopenia - the reticuloendothelial system (largely the spleen) removes antibody-coated platelets, causing a mild to moderate thrombocytopenia (rarely <20,000/mm3).
Arterial and venous thrombus - HIT antibodies activate platelets, resulting in platelet aggregation and the release of procoagulant factors. The risk of thrombus is as high as 50% in untreated HIT.
This patient with sharp chest pain that worsens with inspiration (ie, pleuritic chest pain), tachypnea, and decreased breath sounds over the right lung base likely has an acute pulmonary embolus due to HIT. An embolus in the right lower lobe can cause pain radiating to the epigastrium and right upper quadrant. Management of patients with suspected HIT includes immediate discontinuation of all heparin products and initiation of therapeutic anticoagulation with a nonheparin anticoagulant (eg, fondaparinux in pregnant patients).
(Choice A) Acute fatty liver of pregnancy can present with right upper quadrant pain and thrombocytopenia; however, patients with this condition also have elevated aminotransferases due to fulminant liver failure, which are not seen in this patient.
(Choice B) HELLP (Hemolysis, Elevated Liver enzymes, and Low Platelet count) syndrome can present with thrombocytopenia; however, affected patients typically have additional laboratory abnormalities (eg, hemolytic anemia, elevated transaminases). This patient's hemoglobin and liver transaminases are normal for pregnancy, making this diagnosis less likely.
(Choice D) Preeclampsia with severe features can cause right upper quadrant pain and thrombocytopenia. However, patients with preeclampsia with severe features typically have hypertension (systolic pressure ≥160 mm Hg or diastolic pressure ≥110 mm Hg) and elevated creatinine (reflecting end-organ damage due to hypertension).
(Choice E) Thrombotic thrombocytopenic purpura can present with thrombocytopenia and abdominal discomfort; however, patients typically have fever, purpura, elevated creatinine, and neurologic findings (eg, weakness, confusion). In addition, platelet counts are usually <10,000/mm3.
Educational objective:
Heparin-induced thrombocytopenia typically presents with mild-moderate thrombocytopenia and paradoxical thrombosis (eg, pulmonary embolus) within 5-10 days of heparin initiation.