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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.

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Presentation on theme: "Nucleic Acid Amplification Test for Tuberculosis Heidi Behm, RN, MPH Acting TB Controller HIV/STD/TB Program Oregon, Department of Health Services."— Presentation transcript:

1 Nucleic Acid Amplification Test for Tuberculosis Heidi Behm, RN, MPH Acting TB Controller HIV/STD/TB Program Oregon, Department of Health Services

2 What is this test? Nucleic Acid Amplification Test (NAAT) identifies genetic material unique to MTB Nucleic Acid Amplification Test (NAAT) identifies genetic material unique to MTB Several NAA test have been FDA approved 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 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 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 Oregon State Public Health Lab (OSPHL) will utilize Gen Probe MTD-2 NAAT is also referred to as Polymerase Chain Reaction (PCR) test. NAAT is also referred to as Polymerase Chain Reaction (PCR) test.

3 Why is NAAT so great? TB genetic material can be detected using NAAT within 3-5 hours while cultures take weeks! 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 Find out faster if smear+ is TB vs. NTM (save time and money on drugs, contact investigation, etc) (save time and money on drugs, contact investigation, etc) Earlier diagnosis for smear- Earlier diagnosis for smear- (less delayed diagnosis and TB transmission, decrease the inappropriate use of fluoroquinolones) (less delayed diagnosis and TB transmission, decrease the inappropriate use of fluoroquinolones) It’s easy (no extra sputum needed)! It’s easy (no extra sputum needed)! It’s free for LHDs! It’s free for LHDs!

4 How will this work for LHDs? Collect sputum to rule out TB and send to lab as usual Collect sputum to rule out TB and send to lab as usual OSPHL will test the first sputum with NAAT 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. 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 Others tested by special request only If you do not want sputum tested, indicate on lab slip If you do not want sputum tested, indicate on lab slip

5 How do private providers order NAAT? Processed sediments may be sent to OSPHL directly from the lab or hospital Processed sediments may be sent to OSPHL directly from the lab or hospital There will be a charge of $40.00 for testing There will be a charge of $40.00 for testing The provider should contact OSPHL at The provider should contact OSPHL at or see OSPHL web site for further instruction.

6 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) 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 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 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% Do not use if low suspicion of TB (example, B waiver). Positive predictive value of the NAA test is <50%

7 What is NAAT MTD-2 FDA approved for? Smear+ sputum specimens Smear+ sputum specimens Smear- sputum specimens Smear- sputum specimens Patients who haven’t received TB treatment Patients who haven’t received TB treatment Patients who are highly suspected to have TB Patients who are highly suspected to have TB Isn’t approved for non-respiratory specimens, but there may be clinical utility in using test 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) Further research needed on using for children who cannot produce sputum (gastric aspirates)

8 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=95%, Specificity=98% Respiratory smear- specimens from untreated patients with high suspicion for TB. Respiratory smear- specimens from untreated patients with high suspicion for TB. Sensitivity=66%, Specificity=98% Sensitivity=66%, Specificity=98%

9 How good is NAAT continued… Good test for smear+ Good test for smear+ Sensitivity for smear- is low (66%) Sensitivity for smear- is low (66%) A test with high sensitivity catches all people with a disease. 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) 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 MTD-2 detects only 50%--80% of AFB smear- negative, culture-positive pulmonary TB cases

10 Interpretation of Results Not a perfect test. Not a perfect test. Does not replace culture results which are the “gold standard”. 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 Interpret within the context of the patient’s symptoms, chest x-ray, smear and culture

11 Smear+, NAAT+ Presume active TB disease Presume active TB disease Start contact investigation Start contact investigation Start TB medication Start TB medication Keep in isolation until cleared Keep in isolation until cleared Confirm by culture result Confirm by culture result

12 Smear+, NAAT- Suspect nontuberculous mycobacterium (NTM). Suspect nontuberculous mycobacterium (NTM). Does not rule out TB Does not rule out TB Consider delaying treatment, contact investigation and removing from isolation. 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. 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 Confirm findings with culture result

13 Smear-, NAAT+ Likely has active TB disease Likely has active TB disease Consider submitting another specimen for NAAT to verify Consider submitting another specimen for NAAT to verify Presumed to have TB if two or more specimens are NAAT positive 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. Use clinical judgment to determine whether to start treatment, start contact investigation and place on isolation. Confirm by culture result Confirm by culture result

14 Smear-, NAAT- For smear- specimens, sensitivity is low For smear- specimens, sensitivity is low Diagnosis of TB cannot be excluded Diagnosis of TB cannot be excluded Rely on clinical judgment Rely on clinical judgment Requesting a second NAAT may be helpful 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. 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 Confirm by culture result

15 Inhibited NAAT Amplification was inhibited due to a naturally occurring inhibitor in the specimen or processing reagent (example: blood). Amplification was inhibited due to a naturally occurring inhibitor in the specimen or processing reagent (example: blood). Can result in a false negative Can result in a false negative Test for inhibitors will be automatically run by lab on all smear+, NAAT- specimens 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 If present, lab will contact you for additional specimen to test

16 Conclusion

17 Conclusion NAAT will provide LHDs with additional information to base decisions upon 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 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 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! The TB Program is available to assist with interpretation of results!

18 Resources State summary: AATguide.pdf State summary: AATguide.pdf AATguide.pdf AATguide.pdf OSPHL: df OSPHL: df df df CDC: ml/mm5801a3.htm?s_cid=mm5801a3_e CDC: ml/mm5801a3.htm?s_cid=mm5801a3_e ml/mm5801a3.htm?s_cid=mm5801a3_e ml/mm5801a3.htm?s_cid=mm5801a3_e


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