Billing and Coding: Influenza Diagnostic Tests

To avoid the overuse of antibiotics and the potential risk of antibiotic
resistance, point of care providers should consider testing patients prior to
prescribing treatment for a bacterial or influenza infection. Influenza
testing (using molecular methods) is recommended for hospitalized patients
with suspected influenza. However, testing is not needed for all outpatients
with signs and symptoms consistent with influenza before making antiviral
treatment decisions, particularly once influenza activity has been documented
in the community. The following summary provides a list of the main available
types of diagnostics tests:

**Rapid Antigen Tests:**

  * Available at the point of care
  * Yields a Flu A and Flu B result in < 30 minutes
  * Less sensitive (50%-70%) and specific (90%-95%) compared to other methods and may require confirmation by reverse transcription-polymerase chain reaction (RT-PCR) or viral culture. **Note:** the Food and Drug Administration (FDA) now requires that all Rapid influenza diagnostic tests (RIDTs) achieve 80% or higher sensitivity compared with RT-PCR.
  * Centers for Disease Control and Prevention (CDC) recommendations:
    * Use rapid diagnostic tests with high sensitivity and specificity.
    * Collect respiratory tract specimens as early in the illness as possible (within 3-4 days of illness onset).
    * Follow manufacturer's instructions, including handling of respiratory specimens, as described in the device package insert.
    * Consider sending respiratory specimens (from symptomatic patients) for RT-PCR to confirm results of RIDTs, especially in the following situations:
      * When community influenza activity is low and the rapid diagnostic test result is positive.
      * When community influenza activity is high and the rapid diagnostic test result is negative.

_Contact your local or state health department for information about influenza
activity._

  *     *       * A patient has had recent close exposure (this does NOT include eating cooked meat) to pigs or birds (including poultry) or other animals, and there is concern for infection with a novel influenza A virus.

**Targeted Molecular Methods:**

  * Uses RT-PCR or other amplification methods to detect viral nucleic acids
  * Results available in < 24 hours (often in less than 2-4 hours)
  * Detects from 1-2 to up to 20 respiratory pathogens from 1 specimen
  * A positive result (on testing of an upper respiratory tract specimen) in a person who recently received intranasal administration of live attenuated influenza virus vaccine (LAIV) may indicate detection of vaccine virus.

**Viral Culture:**

  * Confirms present active infection
  * Results available in 3-10 days
  * Misses opportunity for Oseltamivir (Tamiflu) treatment for positive patients

**Immunofluorescence (IF) - Direct (DFA) or Indirect (IFA) Fluorescent
Antibody Staining (antigen detection):**

  * Moderate sensitivity and high specificity
  * Results available in approximately 2-4 hours

If a rapid antigen test is performed and then confirmed using PCR, the second
test may require the -59 modifier.

If a CLIA-waived test is performed, the -QW modifier should be reported for
the waived test.

**Reference:** Centers for Disease Control and Prevention. [Information for
Clinicians on Rapid Diagnostic Testing for
Influenza](http://www.cdc.gov/flu/professionals/diagnosis/rapidclin.htm).
Accessed 4/27/21.