According to a study, Israeli researchers noted that a novel method that estimates the rate at which a patient's serum C-reactive protein (CRP) level changes over time is more effective than absolute serum CRP concentration at differentiating bacterial and non-bacterial febrile infections. The researchers defined the new parameter called CRP velocity as the ratio created by dividing the CRP value when a patient presents with an acute febrile disease by the number of hours since the onset of fever. Previously, the authors note that analogous methods have been used, citing as an example the time of onset of chest pain being crucial for accurately interpreting cardiac enzyme levels when evaluating patients with acute coronary syndrome. The study cohort involved 178 adults who presented with acute fever (oral temperature of 38.0C or higher) to the emergency department at the authors' hospital. Patients were excluded if they had a malignancy or HIV infection, had been taking antibiotics, or did not know with certainty when fever began. Of the 178 participants, 108 had febrile bacterial infections (primarily pneumonia or urinary tract infections) and 70 had non-bacterial febrile illnesses (primarily unspecified viral infections, upper respiratory tract infections/bronchitis or gastroenteritis/colitis). This classification was done retrospectively by two infectious-disease specialists who were blinded to the CRP findings. As expected, the patients with bacterial infections had significantly higher absolute CRP levels compared with patients who had non-bacterial febrile illnesses. In addition, those with bacterial infections also had significantly higher CRP velocity values (P < 0.001). The researchers used receiver operating characteristic curve analysis to compare absolute CRP and CRP velocity as methods for differentiating between bacterial and non-bacterial febrile illness. The areas under the curve for the 2 methods were 0.783 and 0.871, respectively. This advantage for CRP velocity was even more pronounced in an analysis of a subgroup of patients with CRP concentrations of less than 100 mg/L. The authors noted that this is a diagnostic improvement significant with no additional cost, because it needs only some additional information, although this information will not always be available.