The Karius Test™

Frequently Asked Questions

The Karius Test

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About Karius

Karius is a life sciences company focused on generating genomic insights for infectious diseases with a non-invasive blood test that helps clinicians make rapid treatment decisions. By mapping each patient’s microbial landscape from a single blood draw, Karius moves closer to a vision of a world where infectious disease is no longer a major threat to human health. The Karius laboratory is CLIA-certified and CAP-accredited to perform high-complexity clinical laboratory testing.

The Karius Test, a laboratory service performed at our Redwood City, CA, facility, uses proprietary sample preparation, next-generation sequencing (NGS), and analytics for the broad and rapid detection of microbial cell-free DNA from a standard blood draw. Unlike conventional culture and panel testing methods that identify a narrow range of pathogens, the Karius Test can detect more than 1000 pathogens. Our pathogen database is curated for sequence quality and clinical relevance. The test is broad-based, which means that co-infections can be detected.

Pathogens we can detect are: bacteria, fungi, DNA viruses, and eukaryotes (including protozoa). The complete list can be found here:

Infecting pathogens leave traces of their genetic material in blood as cell-free DNA (cfDNA). The Karius Test isolates, identifies, and quantifies the microbial cfDNA signal found in blood. Testing itself consists of: 1) specimen processing, 2) next-generation sequencing, 3) sequence analysis, and 4) reporting.

During specimen processing, cell-free DNA fragments from the plasma specimen are extracted and converted to shotgun DNA sequencing libraries. Next, the DNA is sequenced using Illumina NextSeq technology. Finally, during analysis, the absolute concentration of cfDNA from each pathogen is calculated and compared to controls to determine which microbes are contributing significant levels of cfDNA to the specimen. Reporting consists of confirming several quality control indicators and, upon acceptable performance, faxing the result back to the ordering institution, typically the day after specimen receipt.

Karius reports only the organisms from which cfDNA is detected in statistically significant amounts relative to controls run alongside every sample in every batch. One or multiple microorganisms may be on the report.

Clinical Questions

Cell-free DNA technology has been used successfully in noninvasive prenatal testing (NIPT), organ transplant rejection screening, and oncology liquid biopsies. Karius has developed this technology for use in infectious disease diagnostics.

Cell-free DNA from pathogens can be found in blood regardless of the site of infection. By sequencing cell-free DNA circulating in the plasma, biopsies to obtain intact pathogens may be avoided.

Applications of the Karius Test include:

  • Infections in immunocompromised patients
  • Complicated pneumonia
  • Endocarditis

Currently, the Karius Test is validated only for blood plasma specimens. However, this does not mean that we can only detect bloodstream infections. We have found that even when an infection is localized in the CSF, in the lung, or in a deep abscess, pathogen cfDNA from that infection can be detected in the plasma.

The Karius Test can detect cell-free DNA (cfDNA) from dead and dying pathogens released into the bloodstream. Therefore, the cfDNA signal of a pathogen may still be detected even when a patient has been pre-treated with antibiotics.

Currently, the Karius Test offers detection of methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-sensitive Staphylococcus aureus (MSSA). In the event that insufficient sequence data are available then the test reports an indeterminate result.
The Karius Test detects fragments derived from the SCCmec resistance marker within the S. aureus genome harboring the mecA/C resistance gene.


You can reach us 24/7 by phone at 1-866-452-7487or by email at [email protected].

Karius is a Clinical Laboratory Improvement Amendments (CLIA)-certified clinical diagnostic laboratory. We offer infectious disease testing in every state in the United States, including permits and licenses to provide our testing services in states that require them, such as New York, California, Maryland, Rhode Island, and Pennsylvania.

Please see our Licensure Page, for more information and to download copies of Karius’s licenses and certifications.

Typically, specimens received at our laboratory by 8:30 AM Monday through Saturday are reported the next day (Monday-Sunday).

Our laboratory process requires that a specimen being tested passes all of our stringent quality control (QC) metrics before its result is reported. If a specimen fails to meet any of the internal QC standards, it is re-processed. This means the reporting of the result will be delayed.

Please contact Karius for information on pricing.

Please contact Karius at [email protected] to create an account. To onboard your institution, we will need the following information:

  • Institution Name
  • Address
  • Phone Number
  • Fax Number
  • Billing Contact
  • Email Address for login credentials

Package the specimen along with a printed Karius Test Requisition Form using packaging and transportation supplies provided by Karius. Specimens should be shipped at ambient temperature and should arrive at Karius within 4 days (96 hours) of draw.

We recommend that specimens be shipped via FedEx First Overnight® to ensure that the specimens are received at Karius before 8:30 AM. Karius covers FedEx First Overnight® fees. You can use the FedEx pre-printed airbills included in our kits or select the option to print a FedEx label when you submit the requisition online.

Specimen Questions

If you already have login credentials given to you by Karius, please log in using those credentials here:

If you don’t have a login, please contact Karius at [email protected].

Our preferred method of specimen collection is in a BD Vacutainer Plasma Preparation Tube (PPT).

  1. Collect 5-mL whole blood in PPT tube and invert 8-10 times.
  2. Within 6 hours of the draw, spin PPT tube at 1100 RCF for 10 mins at room temperature. (Separated plasma in PPT tube is stable at room temperature for up to 96 hours after draw.)
  3. Ship specimen at ambient temperature via FedEx First Overnight® service to Karius.

You can find more information about specimen collection here:

If the gel plug in the PPT tube does not move to separate the cells from the plasma, the tube should be re-centrifuged at a higher speed. Check to make sure that the setting on your centrifuge is set at RCF or g, and not RPM, before recentrifuging at 1100 RCF (g).

If the specimen is collected in a PPT tube, after centrifugation, the tube can be frozen as is without transferring the plasma into a separate tube. If the specimen is collected in a K2-EDTA tube, transfer the plasma into a sterile polypropylene tube after centrifugation before freezing.

If the specimen is frozen and shipped on dry ice, the specimen can be received at Karius anytime after the draw.

Specimens are rejected if:

  • They do not meet our minimum volume criteria (700 uL of plasma)
  • Plasma was separated from whole blood >6 hours after draw
  • Plasma was received at Karius at ambient temperature >4 days after draw
  • Specimen has fewer than 2 patient identifiers on the tube
  • Specimen was collected in a tube beyond its expiration date
  • Specimen has incomplete or improper separation of plasma

Test Results

On the Karius Test report, the results include the name of any microorganism(s) detected at statistically significant levels, the DNA molecules per microliter (MPM), and the reference MPM range. MPM refers to the number of microorganism DNA fragments present in one microliter of plasma. The reference range represents the 97.5th percentile MPM concentration detected in plasma specimens from asymptomatic individuals for each microorganism present.

A positive result will list the MPM detected for each microorganism in the patient specimen received at Karius. A negative result means that no cell-free DNA of any microorganisms in our database was detected in statistically significant amounts. This does not mean that the patient is infection-free.

The reported organisms may or may not be the cause of patient infection. Results should be interpreted within the context of clinical data, including medical history, physical findings, epidemiological factors, and other laboratory data.

Karius does not provide recommendations on the management or treatment of specific patients. As with any diagnostic test, the Karius Test should be interpreted in the context of your patient’s clinical picture to determine clinical significance.

Our Medical Affairs team is available for consultation and happy to provide you with references to literature that describe the pathogen, its spectrum of disease, and treatment options. This information might help you determine how best to use the Karius Test result to guide the care of your patient.

Please contact Medical Affairs at [email protected] or 866-452-7487.

There are two reasons why a “No result” is reported:

  1. The specimen did not meet our minimal acceptance criteria and was rejected upon receipt.
  2. The specimen did not meet our internal quality control standards during its testing.


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