Final answer:
Thrombocytopenia is the lab abnormality indicating an increased risk of death in Rocky Mountain spotted fever, a disease marked by a petechial rash and caused by Rickettsia rickettsii.
Step-by-step explanation:
The abnormality in laboratory findings associated with an increased risk of death in patients with Rocky Mountain spotted fever (RMSF) is thrombocytopenia. RMSF is a severe tickborne disease caused by the bacterium Rickettsia rickettsii, which can cause a range of symptoms, including a characteristic petechial rash that begins at the extremities and can spread to the trunk. A low platelet count, or thrombocytopenia, contributes to the bleeding tendencies seen in severe cases and is a predictor of poor prognosis. Other laboratory findings in RMSF may include hyponatremia, elevated liver enzymes, and less commonly, hypokalemia, but thrombocytopenia is specifically noted as being indicative of an increased risk of fatality.