2 Step PPD Test

Some people may have significant redness and swelling where the tuberculin protein was injected. This is more common in persons who have previously had a positive PPD test and then get the test again by accident.

In persons who have never been exposed to PPD, this response to tuberculin protein is extremely uncommon.

A two-step PPD is read the same way as a 1-step PPD. The redness and the induration are measured and documented. There has to be a 7-10 day gap between the first and the second PPD of the 2 step PPD series.

Yes. You need a Chest X-Ray if any of the PPD turns positive. So, if your first PPD is read as a positive PPD, you don’t need to do the second PPD in the 2-step PPD series. Instead, you will need a Chest X-Ray for the positive PPD reading.

Also, for healthcare workers and other non-immunocompromised patients, a negative PPD reading is any induration 10 mm or less.

However, for Immigration Medical Exam purposes, any PPD more than 4 mm is considered to be a positive PPD reading. A lot of doctors fail to write the mm and the record just shows a positive PPD reading or a negative PPD reading – this is insufficient for Immigration Medical Exam paperwork.

There is a relatively new and expensive blood test called IGRA, which has been available for testing for TB and screening for exposure to tuberculosis for a few years now. Nao Medical can draw your blood and send it for the IGRA test once you have pre-paid for the test. It is also called a Quantiferon Gold Test.

Tuberculosis screening may be done with any approved test to detect M. tuberculosis infection, such as the tuberculin skin test (TST), or one of the whole blood interferon-gamma release assays (IGRAs) approved by the Food and Drug Administration (FDA).

Interferon-Gamma Release Assays (IGRAs) or Quantiferon Gold Test for TB

As per the CDC “IGRAs are used to determine if a person is infected with M. tuberculosis by measuring the immune response to tuberculosis proteins in whole blood. Specimens are mixed with peptides that simulate antigens derived from M. tuberculosis and controls. In a person infected with M. tuberculosis, the white blood cells recognize the simulated antigens and release interferon-gamma (IFN- γ); results are based on the amount of IFN- γ released.”

The Food and Drug Administration (FDA) has approved the following IGRAs in the United States:

• QuantiFERON®-TB Gold, 2005
• QuantiFERON®-TB Gold In-Tube test (QFT-GIT), 2005;
• T-SPOT® TB test, 2008

Some advantages of IGRAs include the following:

• IGRA requires just one visit for TB testing. IGRAs are therefore the preferred method of testing for groups of people who have poor rates of return for TST reading and interpretation (e.g., homeless persons).
• IGRAs do not cause booster phenomenon.
• IGRA results can be available earlier than 48 hours.
• IGRA is unaffected by environmental mycobacteria.

Some limitations of IGRAs include the following:

• The blood sample must be processed within 8-30 hours after collection.
• Data is limited when used in children younger than 5 years of age, persons recently exposed to TB, immuno-compromised persons, and those who will be tested repeatedly (serial testing).

IGRA Result Interpretation

The interpretation of IGRAs varies by type of IGRA test performed.

• QFT testing is based on the amount of IFN-γ released.
• T-SPOT TB testing depends on the number of cells that release IFN-γ.

Labs provide both the qualitative and quantitative IGRA results.

• Qualitative IGRA results are reported as positive, negative, indeterminate, or borderline.
• Quantitative IGRA results are reported as numerical values that include a response to the TB antigen and 2 controls, nil and mitogen.

If you have no prior history of the test or have had a negative PPD reading previously, then Nao Medical’s healthcare professionals will inject the tuberculin protein into your forearm skin at the first visit. Once the PPD is administered you will need to return in 48-72 hours for a follow-up visit.

At the second PPD visit, the tuberculin test reaction will be read. When you come back to us, let the front desk staff know why you are here and you will be fast tracked into a room. Your PPD will be recorded right away, and you can get done in the shortest possible time.

If you have a PPD form or a physical exam form that needs to be filled out, please bring it with you. Nao Medical providers will fill out your forms once the PPD has been read (second PPD visit).

If you need a chest X-ray for a positive PPD reading, Nao Medical has X-ray on site at each location. End-to-end PPD testing convenience at one location!

Nao Medical does PPD tests all 7 days a week. Nao Medical is open even on holidays. You can walk in and get the PPD test done and return in 2 days for a PPD check. When you return in 48 hours, your forearm will be examined and your form can be completed on the spot. At Nao Medical, you never have to wait!

In countries where TB is common, BCG (Bacillus Calmette–Guérin) vaccine is used to protect infants and young children from serious, life-threatening disease, specifically miliary TB and TB meningitis.

BCG vaccination is not given in the United States. The effect of BCG vaccine on tuberculin skin testing (PPD) results may cause confusion. It is thought that the tuberculin skin test reactivity caused by BCG vaccine gets reduced with the passage of time. However, periodic and repeated skin testing may boost the reactivity to PPD.

The CDC recommends that all PPD positive results be interpreted based on risk stratification regardless of BCG vaccination history.

A person with a history of BCG vaccination therefore can be tested and treated for latent TB if they test positive for a PPD.

IGRAs use M. tuberculosis antigens that do not cross-react with BCG, and therefore, do not cause false positive reactions in people who got BCG in their countries. However, IGRA is an expensive blood test and the data in repeatedly tested individuals is lacking. IGRA is therefore not routinely recommended as a testing modality to screen for TB.

An abnormal or a positive PPD reading only means you have been exposed to the bacteria that cause TB. It does not mean you have disease. You may need further investigation with a chest X-ray to identify if there is any evidence of active disease in the lungs.

After that, treatment may be given to lower your risk of eventually getting TB (reactivation of the disease). A positive skin test for tuberculin does not mean that you have active tuberculosis disease. It only shows that you were exposed to the bacteria that cause TB. More tests need to be done to identify if there is active TB disease.

If you have a newly positive PPD, you will need a chest X-ray. Not to worry, we can do the chest X-ray right away and have it read by a radiologist as well.

Nao Medical does more PPD tests than most other medical offices and all our providers understand the various cutoffs for a positive PPD.

A 5-mm induration is considered to be positive PPD test result for:

• Persons with HIV infection
• Recent contacts of persons with active TB disease
• Persons with evidence of old, healed TB lesions on chest X-rays
• Persons with organ transplants and other immunosuppressed persons, including those receiving prolonged corticosteroid therapy (the equivalent of >15 mg/d of prednisone for one month or more) and TNF-a blockers

A 10-mm induration is considered to be positive PPD test result for:

• Persons who have immigrated within the past 5 years from areas with high TB rates*
• Injection drug users
• Persons who live or work in institutional settings where exposure to TB may be likely, such as hospitals, prisons, homeless shelters, SROs, and nursing homes
• Mycobacteriology laboratory personnel
• Persons with clinical conditions associated with increased risk of progression to active TB, including: silicosis; chronic renal failure; diabetes; more than 10% below ideal weight or BMI < 18.5; gastrectomy/jejunoileal bypass; some hematologic disorders (such as leukemia and lymphomas); and certain cancers (such as carcinoma of the head, neck, or lung, leukemias, and lymphomas)
• Children < 5 years, and children or adolescents exposed to adults in high-risk categories
• Persons with prolonged stay in areas with high TB rates*

A 15-mm induration is considered to be positive PPD test result for:

• Persons at low risk for active TB disease for whom testing is not generally indicated

* Countries with high rates of TB include China, Dominican Republic, Ecuador, Haiti, Honduras, India, Mexico, Pakistan, Peru, Philippines, South Korea, and all of Africa.

You must alert your provider regarding a prior positive PPD result because you may not need any repeat PPD testing for TB and may qualify for a waiver. You will still need to be seen at Nao Medical, as we cannot determine this over the phone.

If you have ever had a positive PPD skin test and/or have a chest X-ray report, please bring it with you. Our front desk staff cannot answer your medical questions. Save them for the provider when you come for the visit.

Yes. As discussed earlier, a PPD test can have different cutoffs based on size and be read as a positive PPD reading or a negative PPD reading. This is why going to the right place can make all the difference.

A positive PPD reading or a negative PPD reading depends on your medical condition, age, risk factors, and also the reason the PPD test was done. For example, USCIS has a different cutoff for immigration purposes. NYC Department of Health has its own guidelines for NYC as tuberculosis is more common in NYC.

You can review the CDC publishes for PPD reading based on the medical diagnosis, age, and other risk factors.

PPD tests are usually for pre-employment purposes and are not covered by health insurance plans. Nao Medical charges $40 for performing the PPD skin test for TB as well as reading the TB test results ($40 covers the two visits). We accept cash and credit card payments.

Not necessarily. Most urgent cares accept walk-in patients. But if you want shorter wait times, you can book an appointment through phone or online.

Yes. You can go to urgent care for consultations, physicals, primary care, lab tests, and more.

If you have no insurance, we provide our services without insurance for self-pay patients, giving you the care when you need it most.