How the BioFire (FilmArray) Test Works
The BioFire FilmArray is a rapid multiplex PCR system that uses nested multiplex RT-PCR technology to simultaneously detect multiple respiratory pathogens (bacteria, viruses, and resistance genes) from a single specimen in approximately one hour, integrating sample preparation, nucleic acid extraction, amplification, and automated analysis in a closed system 1, 2.
Core Technology
The BioFire system employs nested multiplex RT-PCR as its primary methodology 1. This is one of several nucleic acid amplification approaches used in commercial respiratory panels, but BioFire specifically uses this nested approach to achieve high sensitivity while testing for numerous targets simultaneously.
Technical Process
The system performs the following steps automatically:
- Sample preparation and nucleic acid extraction from the respiratory specimen
- Multiplex PCR amplification of multiple pathogen targets in a single reaction
- Real-time detection and analysis of amplified products
- Automated result interpretation with turnaround time of approximately 1 hour 2
This closed, automated system minimizes hands-on time and technical complexity compared to conventional methods.
Specimen Types
The most commonly approved specimen is a nasopharyngeal swab, though other approved specimens include 1:
- Nasal swabs
- Nasal aspirates
- Nasal washes
- Throat swabs
- Bronchoalveolar lavage (BAL) fluid for specific panels (FilmArray Pneumonia Panel) 1, 2
Panel Capabilities
BioFire offers different panel configurations 1:
FilmArray Respiratory Panel
- Detects >4 targets for influenza and noninfluenza respiratory viruses
- Can include select atypical bacterial pathogens
FilmArray Pneumonia Panel Plus
- Detects 27-34 clinically relevant respiratory pathogens 2
- Includes bacterial targets, viral targets, and 7 genetic markers for antimicrobial resistance 2
- Provides semi-quantitative analysis (reported as copies/mL) 2
Diagnostic Performance
Recent studies demonstrate strong performance characteristics:
- Sensitivity: 89-100% for bacterial detection 2, 3
- Specificity: 90-99.7% across different targets 2, 4, 3
- Overall accuracy: 97.63% for pneumonia panel 3
The system showed 100% sensitivity and 90% specificity for bacterial targets in HAP cases 2, and 96.5% sensitivity and 99.7% specificity for blood culture identification 4.
Clinical Advantages Over Conventional Culture
Detection rate superiority: The PN panel detected pathogens in 54% of samples versus 33.9% by conventional culture, with 20.2% of samples positive only by PN panel 3. This represents significant added diagnostic yield.
Time advantage: Results available in ~1 hour versus 24-72 hours for culture 2, 3.
Viral detection: Identifies viral pathogens (22% detection rate in one study) that conventional cultures miss entirely 2.
Resistance marker detection: The pneumonia panel showed 97% positive percent agreement and 95% negative percent agreement with standard antibiotic sensitivity testing for resistance genes 2.
Important Limitations
Upper respiratory tract sampling limitations: Upper respiratory tract testing is not sufficiently sensitive to exclude lower tract infections, particularly in critically ill and immunocompromised patients 1. Certain influenza strains (H1N1, H5N1) preferentially infect the lower respiratory tract and may be missed by nasopharyngeal sampling 1.
Discordance in immunocompromised patients: High rates of discordance between upper and lower respiratory specimens occur for adenovirus (100%), human metapneumovirus (44%), rhinovirus (34%), and parainfluenza virus type 3 (28%) 1.
Semi-quantitative limitations: While the system provides semi-quantitative data, the concordance rate with culture quantification was only 47.4% in one study 2. Cross-platform Ct value comparisons should be interpreted cautiously 5.
Lower sensitivity for specific organisms: Reduced sensitivity noted for Enterobacter cloacae complex (57.14%) and Klebsiella pneumoniae group (75%) 3.