Pathology/Lab Coding Alert

Distinguish tuberculosis disease from latent TB.

With updated tuberculosis (TB) testing guidelines now available from the Centers for Disease Control and Prevention (CDC), you might need to apprise your lab personnel of the impact on relevant procedure and diagnosis coding.

Study the following testing recommendations to learn what you could face when reporting testing for latent or active infection with Mycobacterium tuberculosis (Mtb).

Look for Latent Testing Expectations

Latent TB is when an individual has an Mtb infection, but does not exhibit symptoms. Clinicians want to identify these cases because such patients may transmit the infection, and their condition may progress to full-blown disease.

Although the tuberculin skin test (TST) has been the historical first line of defense in TB testing, the new CDC recommendations call for testing first with the interferon-γ release assay (IGRA) in many cases. Specifically, the guidelines suggest that when the physician determines that it’s appropriate to test for latent TB infection, the initial test should be the IGRA when the patient meets the following criteria:

• Aged 5 years or older
• Likely to be infected with Mtb
• Low or intermediate risk of disease progression
• Has a history of BCG vaccination
• Is unlikely to return for a TST reading.

Caveat: The guidelines indicate initial testing, when indicated, using TST if the prior conditions aren’t met, or if the IGRA test is unavailable or cost prohibitive.

Lab method: The IGRA test measures the blood’s cell-mediated immune response — secretion of a cytokine called gamma interferon — to TB-specific proteins. The method for measuring the T-cell response is enzyme-linked immunosorbent assay (ELISA).

Advantage: This blood test is useful for people who have had prior Bacillus Calmette Guerin (BCG) vaccination because the test measures immune response to two TB-specific proteins — ESAT-6 and CFP-10 — that were never included in the BCG vaccine. These proteins are also absent from most non-tuberculous mycobacteria, thus avoiding false-positive results for exposure to other mycobacteria. The TST may show false positives for BCG-vaccinated individuals.

Know the codes: For the TST test, you should report 86580 (Skin test; tuberculosis, intradermal). CPT^® deleted the code for the older “tine” test several years ago, leaving this as the sole code for a TST. You might also see the test called a Mantoux test or a PPD (purified protein derivative) test.

For the IGRA test, you should list 86480 (Tuberculosis test, cell-mediated immunity antigen response measurement; gamma interferon).

Diagnosis: You should not code an active TB case based on the results of STS or IGRA testing. Instead, you can report findings using a code such as R76.1- (Nonspecific reaction to test for tuberculosis…).

Learn More Codes for Active Infection

When a TST or IGRA test indicates infection with Mtb, that doesn’t mean the patient has an active TB infection. Clinicians should follow a positive test result with evaluation of symptoms and with tools such as a chest x-ray. When these indicate active TB, clinicians should proceed with sputum collection for testing.

The new guidelines recommend performing acid-fast bacilli (AFB) stain microscopy on sputum for all patients with suspected pulmonary TB. The lab would perform and code this test as 87206 (Smear, primary source with interpretation; fluorescent and/or acid fast stain for bacteria, fungi, parasites, viruses or cell types).

Culture: The gold standard for active TB infection diagnosis is a positive culture that isolates the Mtb organism from a respiratory or other specimen.

“You should report a TB culture using 87116 (Culture, tubercle or other acid-fast bacilli [e.g., TB, AFB, mycobacteria] any source, with isolation and presumptive identification of isolates)” says William Dettwyler, MT AMT, president of Codus Medicus, a laboratory coding consulting firm in Salem, Ore.

Look to NAATs: The downside of an Mtb culture is the time it takes to get a result. For that reason, the new CDC guidelines recommend performing nucleic acid amplification tests (NAATs) to more quickly identify Mtb in respiratory specimens.

Acceptable NAATs for TB diagnosis include the Hologic Amplified Mycobacteria Tuberculosis Direct (MTD) test and the Cepheid Xpert MTB/Rif test.

You should report these tests using 87556 (Infectious agent detection by nucleic acid [DNA or RNA]; mycobacteria tuberculosis, amplified probe technique). For similar tests using direct probe or quantification, look to 87555 or 87557 in the same code family.

Specimen concentration: Labs often concentrate a respiratory specimen before performing tests such as culture or molecular testing. Don’t forget to report 87015 (Concentration [any type], for infectious agents) if your lab performs the concentration step.

Diagnosis: Coding for respiratory tuberculosis is fairly easy. “Start with code A15 and it breaks down simply to A15.0 – A15.9 (Respiratory tuberculosis…),” says Michele Midkiff, CPC-I, RCC, a coding consultant in Mountain View, CA. The fourth digits add greater specificity, such as A15.0 (Tuberculosis of lung) or A15.6 (Tuberculous pleurisy).

Resources: You can find the latest TB testing guidelines, developed with the CDC, the American Thoracic Society and the Infectious Diseases Society of America at https://www.cdc.gov/tb/publications/guidelines/testing.htm.