Tuberculosis (TB) Test Results Frequently Asked Questions

It is important employer to be aware of specific MN statutes related to timelines for retesting (how long a previous test results would be acceptable). That information is available in the manual Regulations for Tuberculosis Control in Minnesota Health Care Settings, July 2013 (PDF) at the Minnesota Department of Health Website Regulations for TB Control in Minnesota Health Care Settings. 

For more information on types of TB tests, see the Centers for Disease Control's (CDC) website: 

1. Testing for Tuberculosis
2. TB Skin Test Fact Sheet
3. TB Skin Test Wall Chart 

Additional information on TB basics including screening and testing is also available on the website: 

1. Tuberculosis (TB)
2. Tuberculin Skin Test (TST)
3. TB Testing (skin test) (Mantoux)
4. TB Blood Test (IGRA) 

First, follow the TB screening rules required for facility licensing (listed in the manual on the MDH website referred to above and in the algorithm at the end of this document). A TB test is the first requirement of the TB screening, and if that test is positive, then a chest x-ray is required. A verbal report of BCG or prior positive test just means their TB status is unknown as you do not have a documented test result. 

Keep in mind, someone who has had the BCG vaccine as an infant is receiving that vaccine because they lived in a country that is endemic for TB. The BCG vaccine does not stop the transmission of TB; it reduces the severity of the disease and prevents death in infants and children. Being from a TB endemic country greatly increases one’s odds of having latent TB infection. BCG is given in infancy and can cause a false positive TB skin test (TST or Mantoux), however, the effect of BCG on TSTs wanes after 10 to 15 years. Therefore, most TSTs have a true result if given 10 to 15 years post vaccine but if an employee is worried their test result being false positive due to BCG, they should be given the TB blood test (IGRA). TB blood tests do not cross react with BCG vaccine. 

The purpose of the TB screening is to identify the presence of active TB or latent TB infection. A chest x-ray alone does not tell us if the individual is baseline positive for TB. Only an accurate TB test combined with a TB symptom screen and chest x-ray as needed can give us that 

information. The purpose of the chest x-ray is to rule out active disease in the lungs, reassuring the provider that although the individual is baseline positive for latent TB infection (dormant, not sick), they can safely provide patient cares as they do not have active TB (sick, may be infectious). 

We heard this question frequently throughout discussions with Providers and understand this can be challenging. TB blood tests (IGRAs) may be in the form of a copy of the lab or documentation from a medical record and usually include qualitative values and quantitative values. You do not need to interpret the quantitative values. Medical providers will use them during the diagnosis process as added information (i.e., a strong positive). All you need to worry about is the qualitative value, which is the actual test result and must be clearly stated as “positive” or “negative”. If results are “indeterminant” or non-conclusive, the test must be repeated. Any positive test result needs a chest x-ray. Acceptable x-rays are those dated within 3 months prior to the date of the positive test or dated after the date of the positive test. The reported results of the chest x-ray should indicate no presence of disease for further follow up (negative, no TB indicated, within normal values, not indicative of disease, clear). Please reach out to the TB program for questions of diagnostic results (MDH ID mainline, 651-201-5414). 

1. How to interpret test results -CDC 

MN has developed regulations based upon CDC guidance and local epidemiological trends. That said, MN does have a higher TB incidence rate than all our surrounding neighbor states. Recommendation following the Collaborative Systems Change study on TB (and discussed at length during Change Implementation meetings with ALF, and Home Care providers, and other provider advocates) was to revisit the 90-day rule for accepting prior negative tests. This recommendation to extend the time frame is currently being explored.

If you have an employee who only left for a short time span and then returned with no known exposure, there is the possibility to get a waiver to not repeat the TB screening. Email (Sarah.Gordon@state.mn.us) to request a waiver by submitting the prior TB screening details (dates of testing, results, type of test used) and the employees TB risk since the last TB testing (work or personal exposure to pulmonary TB, travel to a TB endemic country for two or more months, military deployment).

Yes!! This is also a topic that was discussed at length during our Change Implementation meetings. Test portability is a concern. It leads to a delay in staff getting on the floor to start care duties and is unnecessary cost for providers. Let’s talk about all the different approaches all providers can take to assist with test portability. 

• Ensure new employees always receive their test results.
• We understand most, if not all employees, do not ask for their test results but this is an important piece to portability.
• Making the Employee a copy, scanning and emailing them a copying to their home email account, and/or ensuring the lab provides them a copy of their blood test and/or x-ray
• results is important. This is the employee’s medical health information.
• Educate every employee on the importance of maintaining that record and how long the results are acceptable for. Resources you can provide below.
  • What Should You Know About Your TB Results?
  • TB 101 Training for Health Care Workers CDC
  • Minnesota Standard Consent Form to Release Health Information 

Develop a new policy and procedure to outline a process for employer to share employee TB results with other Health Care employers including a new hire employee consent form and a process for employers to request TB testing status upon hire, request testing results and contact information for TB test results if employee does not have proof of results. Only by employers working together to ensure the workforce can access their prior test results can portability be improved.

A two-step is required as the ‘boosting action’ of the first step on one’s immune system makes the second step a more true result. According to CDC, this boosting action lasts a full 12 months. Therefore, if the individual has a documented negative TST completed within the past 12 months, just do a single TST for a new two-step TST. This new single TST must be done prior to patient cares.

When you give two-step TST, the gold standard is for the second step to be administered 1 to 3 weeks after the first step is read. If the new hire missed the appointment for the second TST, document the miss and the follow up plan to get them tested. The two-step method is the TST requirement for licensing so implement a facility plan to ensure employees return for their second step. Incentives can help with compliance (testing during work hours, use of gift cards, post probationary pay raise, etc.). Switching to the IGRA testing methodology can also ensure compliance.

If a new hire verbally reports (no documentation) having had prior positive TSTs, only test using an IGRA. Repeated TSTs once a person is positive can result in an adverse effect.

If a new hire reports ever having an adverse effect from a TST (swelling, pain, blistering, etc.), only test using an IGRA. Once a person has an adverse effect, repeated exposure to tuberculin can increase the severity, resulting in medical emergencies such as abscesses.

• Do a new TB symptom screen and TB risk history questionnaire.
• Do a TB test (two-step TST or single IGRA)
  • The first TST or the IGRA must be completed and negative prior to patient cares.
  • If individual verbally reports prior positive TST but has no documentation, only give an IGRA.
  • If individual reports any prior adverse reaction to a TST, only give an IGRA.
  • If the TB test is positive, do a chest x-ray.
  • If chest x-ray is abnormal, have a clinician rule out active TB prior to starting work.
  • If the individual is baseline TB test positive, do annual TB symptom screens.
  • If provided verification of TB treatment completion, annual TB symptom screens may be discontinued.
  • For all employees, do annual TB training (symptoms, transmission, infection control). 

• A documented prior positive TB test (does not matter how old the test is).
• A document prior negative chest x-ray if either dated within 3 months prior to the date of the positive TB test or dated any time after the date of the positive TB test.
  • If the new hire only has a chest x-ray but no test, start the screening process over and give a new TB test (IGRA).
• Clinical verification of TB treatment completion may be a substitute for the positive TB test.
  • If provided verification of TB treatment completion, annual TB symptom screens are not required.
• A documented negative IGRA completed within 90 days prior to hire.
  • If the test falls slightly outside of the 90-day range, email sarah.gordon@state.mn.us for a waiver (provide TB risk history).
• A documented negative two-step TST as long as the second step was completed within 90 days prior to hire (and the first step was completed within 12 months of the second step).
  • A documented negative TST completed within the past 12 months. To make the required two-step, complete a new single TST prior to patient cares.