American Board of Internal Medicine (ABIM) Certification Practice Exam

What common laboratory finding is associated with Rocky Mountain spotted fever?

1. Elevated leukocyte count

2. Hypokalemia

3. Thrombocytopenia

4. Hypercalcemia

The correct answer is: Thrombocytopenia

Rocky Mountain spotted fever (RMSF), caused by the Rickettsia rickettsii bacteria, is often associated with specific laboratory findings that assist in its diagnosis. One of the most common findings in patients with RMSF is thrombocytopenia, which refers to a lower than normal platelet count. Thrombocytopenia occurs in RMSF due to the systemic effects of the infection, including the activation of the coagulation cascade and potential consumption of platelets. The infection leads to vascular damage and inflammatory responses that can further consume platelets or disrupt their production in the bone marrow. As a result, monitoring platelet levels can provide crucial diagnostic information when evaluating a patient suspected of having RMSF. Other laboratory findings can include elevated liver enzymes, but the notable association with platelet count is the hallmark of thrombocytopenia in RMSF cases, making it an important aspect of the condition's clinical presentation.