Analytical and Clinical Validation
The analytical and clinical validation of the Karius Test addresses the challenges of bringing a metagenomic infectious disease diagnostic test to clinicians.
The Karius Test® is a non-invasive blood test based on next-generation sequencing of microbial cell–free DNA. It can identify and quantify over 1000 clinically relevant pathogens including bacteria, DNA viruses, fungi, and parasites. Applications include complicated pneumonia, immunocompromised patients, and endocarditis.
The study on the analytical and clinical validation of the Karius Test was published in Nature Microbiology.
The analytical validation study demonstrated that the Karius Test has high detection accuracy and performance across a diverse set of over 1000 microorganisms.
A combination of laboratory and bioinformatics experiments were performed using:
- 580 clinical samples with known infection status
- 350+ contrived infections modeling the most challenging or rare scenarios
- 2600+ computer-simulated microbial cell–free DNA signals
This study presented the clinical validity of microbial cell–free DNA sequencing in plasma as a means of identifying infecting pathogens in patients with suspected sepsis.
The validation showed that the Karius Test:
- can identify a broad range of pathogens in patients with suspected sepsis from a single blood draw
- has improved diagnostic yield, with more causal pathogens identified than all microbiological testing combined
- can potentially provide faster results than conventional testing
High analytical sensitivity and specificity
Analytical Specificity>99.99%per pathogen
Analytical Sensitivity>95%at 35 fragments of cell-free DNA per μL plasma
High analytical specificity of the Karius Test demonstrates quantitative accuracy. Highly optimized processes remove common sources of bias in metagenomic sequencing, resulting in equivalent sensitivity across a wide range of diverse microorganisms.
High quantitative precision and accuracy
Qualitative Precision Within Lab (CV)19.9%
Quantitative accuracy of the Karius Test was determined by comparing the concentration of microbial cell–free DNA, measured as MPM (molecules per microliter) to the quantifiable range of COBAS® Blood CMV qPCR test.1,2
Clinical Validity and Diagnostic Performance
The Karius Test was clinically validated by comparing its performance to the standard-of-care diagnostic workup in the SEP-SEQ Study.1 The study involved 350 patients with suspected sepsis presenting to Emergency Department at Stanford University Hospital.
The performance of the Karius Test was compared to a composite reference standard, which included a combination of:
- Initial blood culture
- Additional microbiological testing
- Urine culture
- Respiratory culture
- PCR testing
- Subsequent blood culture
- Clinical adjudication of test results including radiology results and discharge summaries
High agreement with existing diagnostic tests1
Positive and negative agreement of the Karius Test versus composite reference standard
Note on specificity: Microorganisms related to chronic infections or viral reactivations such as HPV, EBV, CMV, and HHV6, reported by Karius, were deemed unlikely causes of sepsis and therefore categorized as composite reference standard Negative (-). Among positive reports, over 70% reported less than 2 microorganisms.
Positive Karius Test results include fastidious bacteria, viruses, and eukaryotic pathogens. Unlike conventional culture techniques, the Karius Test detects cell-free DNA and therefore is able to identify pathogens even when prior antimicrobial treatment has sterilized blood cultures.
Higher diagnostic yield when compared to blood culture and other microbiological testing1
True positive results in patients with suspected sepsis as defined by the clinical adjudication panel
The Karius Test identified:
- 2.7x more causal pathogens than initial blood culture
- 1.3x more causal pathogens than all microbiology tests
Potentially faster identification of etiology of sepsis than the standard-of-care diagnostic workup1
Comparison of the time to results
Median time from specimen collection to positive findings:
2.5 days | Karius Test
3.5 days | Conventional microbiological testing
1. Blauwkamp TA et al. Nat Microbiol. April 2019;4(4):663-674. doi: 10.1038/s41564-018-0349-6.
2. Blauwkamp TA et al. Evaluation of Karius Plasma Next Generation Sequencing of Cell-free Pathogen DNA to Detect and Quantitate Cytomegalovirus, Epstein-Barr Virus, and BK Virus. ASM Microbe, June 23 2019, San Francisco, CA.