The Science Behind the Accuracy

FebriDx® = 2 Biomarkers

No single biomarker can differentiate a viral from bacterial infection. The FebriDx test utilizes a proprietary combination of two host immune response biomarkers to help accurately differentiate bacterial from viral acute respiratory infection.1

Medical Professional with FebriDx

CRP (C-Reactive Protein) is an acute phase protein that increases during an inflammatory process. Bacterial infection is a potent stimulus of marked CRP elevation with a fast induction time of 4-6 hours.2 Normal CRP concentrations are less than 3 mg/L, however, severe infection or inflammation can cause CRP levels to rise above 500 mg/L.3 It has been demonstrated that 38-56% of patients with viral acute respiratory infections have CRP levels greater than 20 mg/L which may lead to unnecessary antibiotics being prescribed.4 CRP may increase over 100 mg/L with Adenovirus, influenza and COVID-19 infections.4

MxA (Myxovirus resistance protein A) is an intracellular blood protein that is stimulated by interferon alpha/beta.5-6 Interferons are induced by viruses and form an essential part of the immune system’s defense against viral infections.7-8 MxA becomes elevated in the presence of acute viral infections and not in bacterial infections. MxA has a rapid induction time (1-2 hours) and long half-life (2.3 days), making it an ideal marker for viral infection.5

Neither CRP or MxA alone is sensitive or specific to differentiate bacterial from viral infections.7,10-12 At low levels, 20 mg/L, CRP is very sensitive, but non-specific at confirming bacterial infection. At high levels, 80-100 mg/L, the reverse is true.10-12 MxA is specific for viral infections and is not elevated in the presence of a bacterial infection.7-8

By combining the acute phase inflammatory protein, CRP, with a specific viral marker, MxA, the FebriDx test achieves high sensitivity and high specificity to accurately and reliably differentiate bacterial from viral acute respiratory infection.1

At low levels, CRP is non-specific, WHICH CAN LEAD TO overprescription of antibiotics

At high levels, CRP is noT sensitive, meaning patients with bacterial infections COULD be missed

FebriDx dual biomarker technology (CRP + MxA) is highly sensitivE and highly specific

FebriDx is not intended to diagnose any specific bacteria or virus, including SARS-CoV-2.
The test is intended for professional use and should be used in conjunction with other clinical evidence including laboratory, radiographic, and epidemiological information.
Negative results do not preclude respiratory infection and should not be used as the sole basis for diagnosis, treatment, or other clinical and patient management decisions. In addition to utilizing radiography and clinical presentation to aid in diagnosis, additional laboratory testing (e.g., bacterial and viral culture, immunofluorescence, and polymerase chain reaction [PCR]) may be used to confirm the presence of a specific respiratory pathogen.
1. Shapiro NI, Self WH, Rosen J, et al. A prospective, multi-centre US clinical trial to determine accuracy of FebriDx point-of-care testing for acute upper respiratory infections with and without a confirmed fever. Ann of Med 2018;50(5):420-9.
2. Bray C, Bell LN, Liang H, et al. Erythrocyte Sedimentation Rate and C-reactive Protein Measurements and Their Relevance in Clinical Medicine. WMJ 2016;115(6):317-21.
3. Falk, G. and T. Fahey, C-reactive protein and community-acquired pneumonia in ambulatory care: systematic review of diagnostic accuracy studies. Fam Pract 2009;26(1)10-21.
4. Salonen EM, Vaheri A. C-reactive protein in acute viral infections. J Med Virol 1981;8(3):161-7.
5. Ronni T, Melen K, Malygin A, Julkunen I. Control of IFN-inducible MxA gene expression in human cells. J Immunol 1993;150: 1715-26.
6. Simon A, Fah J, Haller O, Staeheli P 1991 Interferon-regulated Mx genes are notresponsive to interleukin-1, tumor necrosis factor, and other cytokines. J Virol 65:968-71.
7. Engelmann I, Dubos F, Lobert PE, et al. Diagnosis of viral infections using myxovirus resistance A (MxA). Pediatrics. 2015;135;e985-93.
8. Haller O, Kochs G. Human MxA protein: aninterferon-induced dynamin-like GTPasewith broad antiviral activity. J Interferon Cytokine Res 2011;31(1):79-87.
9. Horisberger MA. Interferon-induced human protein MxA is a GTPase which binds transiently to cellular proteins. J Virol 1992;66:4705-9.
10. Hatherill M, Tibby SM, Sykes K, et al. Diagnostic markers of infection: comparison of procalcitonin with C-reactive protein and leucocyte count. Arch Dis Child 1999;81:417-21.
11. Andreola G, Bressan S, Callegaro S. Procalcitonin and C-reactive protein as diagnostic markers of severe bacterial infections in febrile infants and children in the emergency department. Pediatr Infect Dis J 2007;26(8):672-7.
12. Korppi M, Kroger L. C-reactive protein viral and bacterial respiratory infection in children. Sc and J Infect Dis. 1993;25(2):207-13.