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Nucleic Acid Amplification Test for Tubeculosis by mikeholy

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									   Nucleic Acid
Amplification Test for
   Tuberculosis
        Heidi Behm, RN, MPH
         Acting TB Controller
       HIV/STD/TB Program
 Oregon, Department of Health Services
               What is this test?
   Nucleic Acid Amplification Test (NAAT) identifies
    genetic material unique to MTB
   Several NAA test have been FDA approved
   1995-Amplified Mycobacterium tuberculosis Direct Test
    (MTD, Gen-Probe, San Diego, California) was FDA
    approved in for AFB smear-positive respiratory
    specimens
   1999-An enhanced test (MTD-2) was approved for
    AFB smear-negative respiratory specimens.
   Oregon State Public Health Lab (OSPHL) will utilize
    Gen Probe MTD-2
   NAAT is also referred to as Polymerase Chain Reaction
    (PCR) test.
       Why is NAAT so great?
  TB genetic material can be detected using NAAT
   within 3-5 hours while cultures take weeks!
 Find out faster if smear+ is TB vs. NTM
  (save time and money on drugs, contact investigation,
   etc)
 Earlier diagnosis for smear-
  (less delayed diagnosis and TB transmission, decrease
   the inappropriate use of fluoroquinolones)
 It’s easy (no extra sputum needed)!
 It’s free for LHDs!
     How will this work for LHDs?
   Collect sputum to rule out TB and send to lab as usual
   OSPHL will test the first sputum with NAAT
   If the first sputum is smear-/NAAT -, but a
    subsequent sputum is smear+ that specimen should
    also get tested.
   Others tested by special request only
   If you do not want sputum tested, indicate on lab slip
      How do private providers order
                NAAT?
   Processed sediments may be sent to OSPHL
    directly from the lab or hospital
   There will be a charge of $40.00 for testing
   The provider should contact OSPHL at
    503-693-4100 or see OSPHL web site for
    further instruction.
When should NAAT not be used?
   Do not use if patient has taken TB medications in
    the past 12 months (not a test of cure, not for
    previously treated B waivers)
   Can detect nucleic acids from dead and live
    organisms, so may remain positive long after
    treatment is completed and the culture is negative
   Do not use if patient has taken TB medications for
    more than 7 days
   Do not use if low suspicion of TB (example, B waiver).
    Positive predictive value of the NAA test is <50%
            What is NAAT MTD-2
             FDA approved for?
   Smear+ sputum specimens
   Smear- sputum specimens
   Patients who haven’t received TB treatment
   Patients who are highly suspected to have TB
   Isn’t approved for non-respiratory specimens, but there
    may be clinical utility in using test
   Further research needed on using for children who
    cannot produce sputum (gastric aspirates)
          How good is this test?
   Respiratory smear+ specimens from untreated
    patients with high suspicion for TB.
    Sensitivity=95%, Specificity=98%

   Respiratory smear- specimens from untreated
    patients with high suspicion for TB.
    Sensitivity=66%, Specificity=98%
How good is NAAT continued…
   Good test for smear+
   Sensitivity for smear- is low (66%)
   A test with high sensitivity catches all people
    with a disease.
   If test has low sensitivity, may believe patient
    does not have disease when they do (a false
    negative)
   MTD-2 detects only 50%--80% of AFB smear-
    negative, culture-positive pulmonary TB cases
     Interpretation of Results
   Not a perfect test.
   Does not replace culture results which are the
    “gold standard”.
   Interpret within the context of the patient’s
    symptoms, chest x-ray, smear and culture
           Smear+, NAAT+
   Presume active TB disease
   Start contact investigation
   Start TB medication
   Keep in isolation until cleared
   Confirm by culture result
              Smear+, NAAT-
   Suspect nontuberculous mycobacterium (NTM).
   Does not rule out TB
   Consider delaying treatment, contact
    investigation and removing from isolation.
   But…if highly suspected of TB or lives in
    congregate setting or with high risk individuals
    request a second NAAT.
   Confirm findings with culture result
              Smear-, NAAT+
   Likely has active TB disease
   Consider submitting another specimen for
    NAAT to verify
   Presumed to have TB if two or more specimens
    are NAAT positive
   Use clinical judgment to determine whether to
    start treatment, start contact investigation and
    place on isolation.
   Confirm by culture result
               Smear-, NAAT-
   For smear- specimens, sensitivity is low
   Diagnosis of TB cannot be excluded
   Rely on clinical judgment
   Requesting a second NAAT may be helpful
   Contact investigation may be delayed and
    patient considered non-infectious if sputum
    smear- x 2 and all NAAT results are negative.
   Confirm by culture result
              Inhibited NAAT
   Amplification was inhibited due to a naturally
    occurring inhibitor in the specimen or
    processing reagent (example: blood).
   Can result in a false negative
   Test for inhibitors will be automatically run by
    lab on all smear+, NAAT- specimens
   If present, lab will contact you for additional
    specimen to test
Conclusion
                 Conclusion
   NAAT will provide LHDs with additional
    information to base decisions upon
   LHDs will not need to do anything different
    when collecting sputum to rule out TB
   Do not use NAAT if the patient has been on TB
    meds. for more than 7 days or was treated
    within last year
   The TB Program is available to assist with
    interpretation of results!
                 Resources
   State summary:
    http://www.oregon.gov/DHS/ph/tb/tools/N
    AATguide.pdf
   OSPHL:
    http://oregon.gov/DHS/ph/phl/docs/guide.p
    df
   CDC:
    http://www.cdc.gov/mmwr/preview/mmwrht
    ml/mm5801a3.htm?s_cid=mm5801a3_e

								
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