Ultrasensitive C-reactive protein is an acute temporal protein synthesized by the liver. Ultrasensitive C-reactive protein should normally be less than ten, and if it reaches more than one hundred, it is highly suggestive of a more serious bacterial infection. Patients with bacterial infections will have elevated ultrasensitive C-reactive protein, whereas viral infections do not cause elevated ultrasensitive C-reactive protein. In addition to bacterial infections causing this phenomenon, in some patients with severe acute myocardial infarction, pulmonary embolism, or massive cerebral hemorrhage or cerebral infarction, there may also be a significant increase in ultrasensitive C-reactive protein. Therefore, there is no way to determine what is the cause of ultrasensitive C-reactive protein alone, and it is necessary to combine the patient’s symptoms and other test results, including medical history, to determine the cause of the disease.