Effective Date: 
Thu, 08/01/2013
Tue, 03/06/2018
Sat, 01/20/2018


Influenza is a highly contagious, acute, viral infection of the respiratory tract. The
causative agents of the disease are immunologically diverse, single-strand RNA viruses known as influenza viruses. There are three types of influenza viruses: A, B, and C.
Type A viruses are the most prevalent and are associated with most serious epidemics. Type B viruses produce a disease that is generally milder than that caused by type A. Type C viruses have never been associated with a large epidemic of human disease. Both type A and B viruses can circulate simultaneously, but usually one type is dominant during a given season.


The Sofia Influenza A+B FIA employs immunofluorescence technology that is used with the Sofia analyzer (Sofia2) to detect influenza virus nucleoproteins. This test allows for the differential detection of influenza A and influenza B antigens.

The patient sample is placed in the Reagent Tube, during which time the virus particles in the sample are disrupted, exposing internal viral nucleoproteins. After disruption, the sample is dispensed into the Cassette sample well. From the sample well, the sample migrates through a test strip containing various unique chemical environments. If influenza viral antigen is present, they will be trapped in a specific location. Sofia will scan the test strip and measure the fluorescent signal by processing the results using method-specific algorithms. Sofia will display the test results (Positive, Negative, or Invalid)


  •  Individually Packaged Cassettes (25): Mouse monoclonal anti-influenza A and anti-influenza B antibodies
  •  Reagent Tubes (25): Lyophilized buffer with detergents and reducing agents
  •  Reagent Solution (25): Ampoules with salt solution
  •  Sterile Nasal Swabs (25)
  •  Small (120 μL), Clear Fixed Volume Pipettes (25)
  •  Large (250 μL), Pink Fixed Volume Pipettes (25)
  •  Influenza A and Influenza B Positive Control Swab (1): Swab is coated with non-infectious recombinant influenza A and influenza B antigens
  •  Negative Control Swab (1): Swab is coated with heat-inactivated, non-infectious Streptococcus C antigen
  •  Package Insert (1)
  •  Quick Reference Instructions (1)
  •  QC Card (located on kit box)
  • Printer Paper (1)


Calibration Cassette (supplied with the Sofia installation pack)


Store the kit at room temperature, 59°F to 86°F (15°C to 30°C), out of direct sunlight. Kit contents are stable until the expiration date printed on the outer box. Do not freeze.


There are three types of Quality Control for Sofia and the Cassette: Sofia Calibration Check procedure, built-in procedural control features, and External Controls.

Sofia "Calibration Check" Procedure:

The Calibration Check Procedure should be performed every 30 days. Sofia is set to remind the user to complete the Calibration Check Procedure.

The Calibration Check is a required function that checks Sofia optics and calculation systems using a specific Calibration Cassette. This Calibration Cassette is supplied with the Sofia installation pack. (It is stored in a protective pouch on the right side of the instrument.  It must be stored in the provided protective pouch.)

  1.  To check the calibration of Sofia, select “Calibration” from the Main Menu.
  2.  Following the prompts, insert the Calibration Cassette into Sofia and close the drawer. Sofia performs the Calibration Check automatically within two minutes with no user input required.

Sofia indicates when the Calibration Check is completed. Select OK to return to the Main Menu.

NOTE: If the Calibration Check does not pass, notify the on-site Supervisor or contact Quidel Technical Support. Technical Support information is easily accessed on the top of the instrument.

Built-in Procedural Controls

The Sofia Influenza A+B FIA contains a built-in procedural control feature. Each time a test is run in Sofia, the procedural control zone is scanned by Sofia and the result is displayed on the Sofia screen. Documentation is automatically logged into Sofia with each test result.

A valid result obtained from the procedural control demonstrates that the test flowed correctly and the functional integrity of the Cassette was maintained. The procedural control is interpreted by Sofia after the Cassette has developed for 15 minutes. If the test does not flow correctly, Sofia will indicate that the result is invalid. Should this occur, review the procedure and repeat the test with a new patient sample and a new test Cassette.

External Quality Control

External Controls may also be used to demonstrate that the reagents and assay procedure perform properly.

Quidel recommends that Positive and Negative External Controls be run:

  •  once for each untrained operator
  •  once for each new shipment of kits – provided that each different lot received in the shipment is tested

When the above conditons are met, order Positive and Negative Rapid Flu QC in the lab computer.

The user must first select Run QC on the Main Menu of Sofia and then, when prompted, scan the QC Card (located in kit box). This card provides information specific to the kit lot, including lot number and expiration date.

Sofia will prompt the user to select the desired mode (WALK AWAY or READ NOW - see explanation in Swab Test Procedure below), and then to run the External Control swabs.

External Positive and Negative Control swabs are supplied in the kit and should be tested using the Swab Test Procedure below.  The instructions can also be found in the Package Insert or the Quick Reference Instructions in the kit.  The Influenza Positive Control Swab contains both influenza A and influenza B antigen. The Positive Control Swab must be run first, followed by the Negative Control Swab.

When the QC test is complete, each result will be displayed as “Passed” or “Failed” for the Positive Control and the Negative Control. Enter results in the lab computer.

Do not perform patient tests or report patient test results if either of the QC test results fail. Repeat the test or contact Quidel Technical Support before testing patient samples.





Use Sterile Foam Tipped swab labeled "Flu" sent down from the Clinic or supplied contol swabs (see above).  Patient samples should be tested as soon as possible after collection.  Check expiration date on the swab and the kit.  Do not use either after the stated expiration date.

1.  Set the Sofia to the desired mode:


In WALK AWAY Mode, the user immediately inserts the Cassette into Sofia. The user then returns after 15 minutes to get the test result. In this mode, Sofia will automatically time the test development before scanning and displaying the test result.


Critically important: Allow the test to develop for the FULL 15 minutes BEFORE placing it into Sofia.

The user must first place the Cassette onto the counter or bench top for 15 minutes (outside of Sofia) and manually time this development step. Then, the user inserts the Cassette into Sofia. In READ NOW Mode, Sofia will scan and display the test result within 1 minute. Note: Results will remain stable for an additional 15 minutes after the recommended development time of 15 minutes.

2.  Dispense all of the Reagent Solution into the Reagent Tube.  Swirl the Reagent Tube to dissolve its contents.

3.  Place the patient swab sample into the Reagent Tube. Roll the swab at least three (3) times while pressing the head against the bottom and side of the Reagent Tube. Leave the swab in the reagent tube for 1 minute.

4.   Roll the swab head against the inside of the Reagent Tube as you remove it. Dispose of the used swab in your biohazard waste.

5.  Fill the provided Small, Clear 120 μL Fixed Volume Pipette with the patient sample from the Reagent Tube. To fill the Fixed Volume Pipette with the patient sample:

  •   FIRMLY squeeze the top bulb.
  •    Still squeezing, place the Pipette tip into the patient sample.
  •    With the Pipette tip still in the patient sample, slowly release pressure on bulb to fill the Pipette.

6.   Firmly squeeze the top bulb to empty the contents of the Small, Clear 120 μL Fixed Volume Pipette into the Cassette sample well. Extra liquid left over in the overflow bulb should be left behind. NOTE: The Fixed Volume Pipettes are designed to collect and dispense the correct amount of liquid sample. Discard the pipette in your biohazard waste.


  1.  Input the User ID (1234) using the on-screen key pad.
  2.  Input the Patient ID and Order #, if applicable, using the barcode scanner or manually enter the data using the on-screen key pad. NOTE: If you mistakenly scan the incorrect barcode, select the field again to re-highlight it. Then simply rescan using the correct barcode, and the previous one will be overwritten with the correct barcode.
  3.  Verify that the correct development mode, WALK AWAY or READ NOW, has been selected. Press and open the Sofia 2 drawer.
  4.  Insert the prepared Test Cassette into the drawer of Sofia 2 and close the drawer.
  5.  Sofia 2 will start automatically and display the progress, as shown in the example below. In WALK AWAY Mode, the test results will be displayed on the screen between 3 and 15 minutes. In READ NOW Mode, the test results will be displayed on the screen within 1 minute. See Sofia 2 Interpretation of Results section.


When the test is complete, the results will be displayed on the Sofia 2 screen. Test Lines, which are fluorescent, cannot be seen with the naked eye.

The Sofia 2 screen will display results for the procedural control as being a “Check Mark” or ”X”, and will individually provide a positive or negative result for both influenza A and influenza B. If the procedural control is “X” retest with a new patient sample and a new Test Cassette.

NOTE: Co-infection with influenza A and B is rare. Sofia Influenza A+B FIA “dual positive” clinical samples (influenza A and influenza B positive) should be re-tested. Repeatable influenza A and B “dual positive” results should be confirmed by virus culture or an FDA-cleared influenza A and B molecular assay before reporting results.

Invalid Result: If the test is invalid, a new test should be performed with a new patient sample and a new test Cassette.

Key Points: 


  •  The contents of this kit are to be used for the qualitative detection of influenza type A and B antigens from nasal swab, nasopharyngeal swab, and nasopharyngeal aspirate/wash samples.
  •  This test detects both viable (live) and non-viable influenza A and B. Test performance depends on the amount of virus (antigen) in the sample and may or may not correlate with viral culture results performed on the same sample.
  •  A negative test result may occur if the level of antigen in a sample is below the detection limit of the test or if the sample was collected or transported improperly.
  •  Failure to follow the Test Procedure may adversely affect test performance and/or invalidate the test result.
  •  Test results must be evaluated in conjunction with other clinical data available to the physician.
  •  Positive test results do not rule out co-infections with other pathogens.
  •  Positive test results do not identify specific influenza A virus subtypes.
  •  Negative test results are not intended to rule in other non-influenza viral or bacterial infections.
  •  Positive and negative predictive values are highly dependent on prevalence. False negative test results are more likely during peak activity when prevalence of disease is high. False positive test results are more likely during periods of low influenza activity when prevalence is moderate to low.
  •  Individuals who received nasally administered influenza A vaccine may have positive test results for up to 3 days after vaccination.
  •  Monoclonal antibodies may fail to detect, or detect with less sensitivity, influenza A viruses that have undergone minor amino acid changes in the target epitope region.
  •  If differentiation of specific influenza A subtypes and strains is needed, additional testing, in consultation with state or local public health departments, is required.
  •  Samples contaminated with whole blood >4% v/v or mucin >0.5% v/v may interfere in the interpretation of the test. Visually bloody or overly viscous samples should not be used.
  •  The performance of this test has not been evaluated for use in patients without signs and symptoms of respiratory infection.


Quidel Sofia Influenza A+B FIA, Reference Instructions, 1219205, (06/17) using:

1. Murphy, B.R., and R.G. Webster. Orthomyxoviruses, In: Fields Virology, 3rd edition, B.N. Fields, D.M. Knipe, P.M. Howley, et al. (eds.), Lippincott-Raven, Philadelphia. 1996, pp. 1397–1445.

2. Biosafety in Microbiological and Biomedical Laboratories, 5th Edition. U.S. Department of Health and Human Services, CDC, NIH, Washington, DC (2007).

3. Henretig F.M. MD, King C. MD. Textbook of Pediatric Procedures, Chapter 123 Obtaining Biologic Specimens Williams and Williams (April 1997).

4. The Clinical Virology Laboratory, Department of Laboratory