Pathology/Lab Coding Alert

Transmission route impacts diagnosis code.

When your lab performs testing for possible West Nile virus (WNV) infection, you need key components in your coding tool-box to make sure you file clean claims.

Read our experts' tips for both diagnosis and procedure coding to get your billing right every time.

Grasp West Nile Virus Basics

Symptoms of WNV infection overlap greatly with many other disease processes, so diagnosis can be difficult. Although up to 80 percent of infected individuals may have mild or no indicators, a subset of infected people may experience encephalitis, which is inflammation of the brain lining, or severe neurological impairment. Conditions that infected individuals experience may include fever, headache, trunk rash, stiff neck, muscle weakness, numbness, lethargy, confusion, convulsions, paralysis, and coma.

Transmission: Patients commonly acquire a WNV infection from a mosquito bite, but other modes of transmission may also come into play. Infection can also spread through blood transfusion, organ transplant, or from mother to child during pregnancy or breastfeeding.

WNV is in genus flavivirus, and is related to other infectious organisms that cause conditions such as dengue fever, yellow fever, Japanese encephalitis, and Zika virus infection.

Antibodies to WNV form in patient blood and other specimens following infection with the organism. Specifically, immunoglobulin M (IgM) typically shows up in patient blood from three to eight days after infection, and may persist in the blood for 30 to 90 days or even longer. On the other hand, IgG antibodies typically appear three weeks after infection and persist in blood for years. These facts come into play in testing and diagnosing WNV infection.

Specify WNV Antibody Test

If your lab performs testing for suspected WNV infection, you have two CPT® codes to choose from depending on the type of test you perform, according to Peggy Slagle, CPC, coding and compliance manager for the department ofpathology/microbiology at the University of Nebraska Medical Center inOmaha:

• 86788, Antibody; West Nile virus, IgM
• 86789, ... West Nile virus.

Specimen: Clinicians typically submit serum or cerebral spinal fluid (CSF) as the specimen for WNV testing.

Interpretation/retesting: If the patient specimen demonstrates the presence of WNV IgM antibodies, it indicates a current active WNV infection. But if no IgM antibodies are present, the clinician may want to retest in about two weeks in case the original test was too early to detect antibody response.

When both IgM and IgG WNV antibodies are present in the patient specimen, that can indicate an active infection that is probably at least three weeks from initial infection. Retesting in two to three weeks should demonstrate declining IgM and rising IgG levels.

If the initial test shows only IgG WNV antibodies, the results indicate the likelihood that the patient had a prior WNV, or possibly other flavivirus, infection.

Common protocol: Because the presence of different Ig classes gives specific diagnostic information with clinical significance, physicians typically order a WNV antibody panel that tests for both IgM and IgG.

Trap: Because 86789 doesn't specify antibody class, you might think that the code describes testing for both IgG and IgM - but you would be wrong, and it would cost you the price of 86788 ($23.11, Clinical Laboratory Fee Schedule National Limit Amount).

Do this: If the lab tests for both IgG and IgM classes for WNV, you should bill both 86788 and 86789.

That's because CPT^® instructions for codes 86602-86804 state that if the lab performs multiple assays "for antibodies of different immunoglobulin classes, each assay should be coded separately."

The instructions then specify how to code the separate assays for IgG and IgM, as follows: "When a coding option exists for reporting IgM specific antibodies, the corresponding nonspecific code may be reported for performance of either an antibody analysis not specific for a particular immunoglobulin class or for an IgG analysis."

Translation: In this case, you should report the IgM test as 86788, and the IgG test using the non-specific antibody code 86789.

Confirm Antibody Test Results

If the patient specimen is positive for WNV IgG and/or IgM, that doesn't absolutely mean that the patient has been infected with the virus. An infection with a related flavivirus can cause cross reactivity that results in a false-positive test for WNV.

That's why the Centers for Disease Control and Prevention (CDC) prescribe follow-up testing for positive WNV antibody tests. Performed by the CDC or certain state public health labs, the assay involves plaque-reduction neutralization tests (PRNTs) on an "acute-phase" specimen taken 3-10 days after symptom onset and "convalescent-phase" specimen taken two to three weeks later.

PRNTs are fairly cumbersome tests that involve diluting the patient specimen and mixing various dilutions with a specific viral suspension placed on host cells and allowed to incubate. Because the virus will grow more on the host cells when less antibody is present, the results can both confirm the type of virus, and confirm an active infection when the neutralizing antibody titer increases significantly between the acute and convalescent phases. The results of this test are the final determination of WNV infection.

Choose Correct Diagnosis Code

You can't assign a West Nile virus infection ICD-10 code based solely on clinical evaluation. Instead, "testing is needed to determine the exact diagnosis," says Mary I. Falbo, MBA, CPC, CEO of Millennium Healthcare Consulting, Inc. in Lansdale, Pennsylvania.

In other words, clinicians need to use the lab test results in addition to clinical presentation to determine the final diagnosis. Labs should ensure that clinicians understand that the patient has a confirmed WNV infection diagnosis only when verified by antibody and confirmatory testing. At that point, clinicians should assign one of the following diagnoses, distinguished by the clinical presentation:

• A92.30, West Nile virus infection, unspecified
• A92.31, ... with encephalitis
• A92.32, ... with other neurologic manifestation
• A92.39, ... with other complications.

If the patient has symptoms of WNV infection and positive antibody testing that has not yet been confirmed, clinicians may appropriately assign a less-specific code based on presentation, such as one of the following:

• A85.2, Arthropod-borne viral encephalitis, unspecified
• A92.9, Mosquito-borne viral fever, unspecified.