County of Monterey Health Department (MCHD) and the California Department of Health (CDPH) recommend the QuantiFERON blood test for people of all ages when testing for TB.

Tuberculin Skin Test (TST) is also occasionally used, but that result is affected by administration of the Bacillus-Calmette-Guerin Vaccine (BCG) producing a positive result in all cases. [BCG vaccine is given to children in countries outside the US where levels of TB are higher. Such as Mexico, the Philippines, Russia, among others. The vaccine is only protective during childhood]

Both tests are commonly called a “TB test”. That is NOT an accurate description.

Active TB is NOT diagnosed by a blood test.

More diagnostics are needed.

• QuantiFERON tests are used to detect latent tuberculosis infections (LTBI). They are not a test for active tuberculosis (TB) disease.
• A negative QuantiFERON result should not be used to rule out TB infection in people with signs and symptoms suggestive of TB disease. It may indicate no evidence of M. tuberculosis infection, but immune system suppression may also cause false negative QuantiFERON results.
• A positive QuantiFERON result indicates exposure to tuberculosis, resulting in a latent tuberculosis infection (LTBI).
• A positive QuantiFERON test will always be positive.
• Even if treatment is received for Active Disease or for LTBI.
• We utilize a statewide database for QuantiFERON and lab testing results for the entire county of Monterey related to infectious disease. And can advise if a client has been tested previously.
•  If blood test is positive, order a 2 view Chest X Ray (CXR) if read as normal. Testing is complete.
• Then algorithm for other routine testing to determine next steps to determine TB vs LTBI.

What laboratory tests should be routinely ordered when testing for TB Infection?

• Order acid fast bacilli (AFB) smear and culture with PCR as soon as TB is suspected. Three consecutive AFB smears and cultures of coughed sputum should be collected at least 8 hours apart.
  • Early morning specimens are preferred, prior to breakfast, if possible, around 5:00 AM – 6:00 AM. Specimen should be obtained before eating, drinking, or smoking to avoid specimen contamination and rejection. At a minimum, 5-10 mL of sputum is required for testing.

What pulmonary imaging should be ordered when ruling out TB?

• A 2-view chest X-ray should be done as part of the diagnostic process to rule out active disease. Red flags that suggest active TB disease include cavitation, most commonly affecting the upper or middle lobes; "tree in bud" nodularity or just nodularity (possible miliary TB); and pleural effusion or loculated pleural effusion.

• CT scan is the preferred diagnostic tool for early diagnosis of TB because it is more sensitive than radiography.

As a patient or provider in the county, we are here for you, so please feel free to call with questions.

 We are available by phone Monday through Friday from 8 am - 5 pm.

Phone numbers 831-202-2066, 831-755-4642.  Fax number: 831-775-8076

Algorithm for Determining Active TB versus LTBI