The Science Behind the Accuracy

FebriDx® = 2 Biomarkers

No single biomarker can differentiate a viral from bacterial infection. FebriDx® incorporates two biomarkers working in conjunction with each other to reliably and accurately differentiate viral from bacterial acute respiratory infection.1-2

Medical Professional with FebriDx

CRP is an acute phase inflammatory protein that is elevated in both viral and bacterial infections. Bacterial infection is a potent stimulus of marked CRP elevation. Normal CRP is less than 3 mg/L.3 It has been demonstrated that 38-56% of patients with viral acute respiratory infections (ARI) have CRP levels greater than 20 mg/L which may lead to unnecessary antibiotics being prescribed.1 CRP levels may increase over 100 mg/L with adenovirus, influenza, and COVID-19 infections.4-5

MxA is an intracellular blood protein that is stimulated by interferon (IFN) alpha/beta.6 Interferons are induced by viruses and form an essential part of the immune system’s defense against viral infections. MxA protein becomes elevated only in the presence of acute viral infections and not in bacterial infections, making it an ideal biomarker for acute viral infections.7

On their own, neither CRP nor MxA is sensitive or specific enough to differentiate viral from bacterial infections.7-14 At low levels, 20 mg/L, CRP is very sensitive, but non-specific, at confirming bacterial infection.8,9,13 At high levels, 80-100 mg/L, the reverse is true.9,11,14
MxA is specific for viral infections and will not be elevated in the presence of a bacterial infection.

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


FebriDx® Multi-Center
Clinical Study

Multi-center prospective clinical trials demonstrated high sensitivity and specificity of FebriDx® in differentiating viral from bacterial acute respiratory infection.

Studies conclude a greater accuracy for differentiating viral and bacterial infections than CRP or procalcitonin alone. FebriDx® has a 97-99% NPV to assist in ruling out a bacterial infection.1-2

Clinical Trial Chart

Acute respiratory infections are diagnosed and managed in GP settings solely by clinical signs and symptoms. Because viral and bacterial infections have similar symptoms, determining diagnosis and treatment by clinical observation alone may lead to misdiagnosis and unnecessary antibiotic treatment.

A FebriDx® test was performed on 21 patients (aged 3 years to 84 years) who had clinical diagnoses of an acute respiratory infection. In each case, a clinical diagnosis was initially made by a GP.

FebriDx® improved the clinical management in 48% (10/21) of the patients, including two patients that were clinically presumed viral but FebriDx® determined a bacterial infection. One of these patients was admitted to the hospital with sepsis.

FebriDx® safely reduced unnecessary antibiotics in 80% (8/10) of clinical cases without any adverse events. FebriDx® was concluded to have high sensitivity and specificity for identifying and differentiating viral from bacterial acute respiratory infection.15

Physician and girl
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 Med. 2018;18:1-10.
2. Self WH, Rosen J, Sharp SC, et al. Diagnostic accuracy of FebriDx: A rapid test to detect immune responses to viral and bacterial upper respiratory infections. J Clin Med. 2017;6(10):E94.
3. Okamura JM, Miyagi JM, Terada K, et al. Potential clinical applications of C-reactive protein. J Clin Lab Anal. 1990;4(3):231-5.
4. Salonen EM, Vaheri A. C-reactive protein in acute viral infections. J Med Virol. 1981;8(3):161-7.
5. Sharifpour M, Rangaraju S, Lin M, et al. C-Reactive protein as a prognostic indicator in hospitalized patients with COVID-19. PLOS One. 2020;15(11): e0242400. https://doi.org/10.1371/journal.pone.0242400
6. Nakabayashi M, Adachi Y, Itazawa T, et al. MxA-based recognition of viral illness in febrile children by a whole blood assay. Pediatr Res. 2006;60:770-4.
7. Engelmann I, Dubos F, Lobert PE, et al. Diagnosis of viral infections using myxovirus resistance A (MxA). Pediatrics. 2015;135;e985-93.
8. 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.
9. 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.
10. Moulin F, Raymond J, Lorrot M, et al. Procalcitonin in children admitted to hospital with community acquired pneumonia. Arch Dis Child. 2001;84:332-6.
11. Korppi M, Kroger L. C-reactive protein viral and bacterial respiratory infection in children. Scand J Infect Dis. 1993;25(2):207-13.
12. Kawamura M, Kusano A, Furuya A, et al. New sandwich-type enzyme-linked immunosorbentent assay for human MxA protein in a whole blood using monoclonal antibodies against GTP-binding domain for recognition of viral infection. J Clin Lab Anal. 2012;26:174-83.
13. Gendrel D, Rayond J, Coste J, et al. Comparison of procalcitonin with C-reactive protein, interleukin 6 and interferonalpha for differentiation of bacterial vs. viral infections. Pediatr Infect Dis J. 1999;18(10):875-81.
14. Virkki R, Juven T, Rikalainen H, et al. Differentiation of bacterial and viral pneumonia in children. Thorax. 2002;57:438-41.
15. Davidson M. FebriDx point-of-care testing to guide antibiotic therapy for acute respiratory tract infection in UK primary care: A retrospective outcome analysis. J Infect Dis Preve Med. 2017;5:165.