Assessing Acute Bacterial vs Viral Infections With C-Reactive Protein Velocity

Researchers conducted a study to determine whether C-reactive protein (CRP) velocity is effective for differentiating between acute viral and bacterial infections in patients with relatively decreased CRP concentrations.

C reactive protein velocity (CRPv) and the second CRP value (CRP2) measured within 24 hours of hospital admission may be effective biomarkers for differentiating between acute bacterial and viral infections. These findings were published in BMC Infectious Diseases.

This retrospective cohort study reviewed patient records collected from the Tel Aviv Sourasky Medical Center in Israel between 2011 and 2019. Patients (N=136) with relatively decreased CRP (£31.9 mg/L) who received antibiotics for a suspected infection were assessed for patterns of CRP. Bacterial infection was defined as a blood culture specimen positive for either Diphtheroids spp, Coagulase-negative Staphylococcus, Streptococcus viridans, or Gram-positive bacilli and viral infection on polymerase chain reaction or immunoglobulin testing.

The researchers calculated CRPv as the difference between the first CRP (CRP1) and CRP2 measurements divided by the time between assessments. Estimated CRP (eCRP) was defined as the expected CRP for each patient on the basis of age and sex. Estimated CRP velocity (eCRPv) was the difference between CRP1 and eCRP divided by the time between CRP1 and symptom onset.

Among patients with bacterial (n=74) and viral (n=62) infections included in the study, the mean ages were 80 and 66 years, 43.2% and 58.1% were women, and CRP1 was 14.8 ± 8.5 and 16.2 ± 8.6 mg/L, respectively.

Compared with patients in the viral infection cohort, the time between symptom onset and CRP1 was increased among patients in the bacterial infection cohort (area under the curve [AUC], 0.75; 95% CI, 0.67-0.82; P <.001). Further comparisons between both patient cohorts showed that those with bacterial infections also had increased eCRPv (AUC, 0.7; 95% CI, 0.62-0.77; P <.001) and CRPv (AUC, 0.86; 95% CI, 0.79-0.91; P <.001). The researchers noted that time between symptom onset and CRP2 also was increased among patients with a bacterial infection (AUC, 0.77; 95% CI, 0.70-0.84; P <.001).

This study was limited by its retrospective design and potential selection bias due to the inclusion of only patients who were treated with antibiotics.

“In patients presenting with relatively [decreased] CRP concentrations but [increased] clinical suspicion of bacterial infection, calculating the rate of rise to first CRP and the dynamics to a second CRP measurement helps in differentiating between bacterial and viral etiologies,” the researchers concluded.


Bernstein D, Coster D, Berliner S, et al. C‑reactive protein velocity discriminates between acute viral and bacterial infections in patients who present with relatively low CRP concentrations. BMC Infect Dis. 2021;21(1):1210. doi:10.1186/s12879-021-06878-y