Presentation on theme: "Nucleic Acid Amplification Test for Tuberculosis"— Presentation transcript:
1Nucleic Acid Amplification Test for Tuberculosis Heidi Behm, RN, MPHActing TB ControllerHIV/STD/TB ProgramOregon, Department of Health Services
2What is this test?Nucleic Acid Amplification Test (NAAT) identifies genetic material unique to MTBSeveral NAA test have been FDA approved1995-Amplified Mycobacterium tuberculosis Direct Test (MTD, Gen-Probe, San Diego, California) was FDA approved in for AFB smear-positive respiratory specimens1999-An enhanced test (MTD-2) was approved for AFB smear-negative respiratory specimens.Oregon State Public Health Lab (OSPHL) will utilize Gen Probe MTD-2NAAT is also referred to as Polymerase Chain Reaction (PCR) test.
3Why 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!
4How will this work for LHDs? Collect sputum to rule out TB and send to lab as usualOSPHL will test the first sputum with NAATIf the first sputum is smear-/NAAT -, but a subsequent sputum is smear+ that specimen should also get tested.Others tested by special request onlyIf you do not want sputum tested, indicate on lab slip
5How do private providers order NAAT? Processed sediments may be sent to OSPHL directly from the lab or hospitalThere will be a charge of $40.00 for testingThe provider should contact OSPHL ator see OSPHL web site for further instruction.
6When 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 negativeDo not use if patient has taken TB medications for more than 7 daysDo not use if low suspicion of TB (example, B waiver). Positive predictive value of the NAA test is <50%positive predictive valueis the proportion of patients with positive test results who are correctly diagnosed. It is the most important measure of a diagnostic method as it reflects the probability that a positive test reflects the underlying condition being tested for
7What is NAAT MTD-2 FDA approved for? Smear+ sputum specimensSmear- sputum specimensPatients who haven’t received TB treatmentPatients who are highly suspected to have TBIsn’t approved for non-respiratory specimens, but there may be clinical utility in using testFurther research needed on using for children who cannot produce sputum (gastric aspirates)
8How 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%
9How 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
10Interpretation 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
11Smear+, NAAT+ Presume active TB disease Start contact investigation Start TB medicationKeep in isolation until clearedConfirm by culture result
12Smear+, NAAT- Suspect nontuberculous mycobacterium (NTM). Does not rule out TBConsider 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
13Smear-, NAAT+ Likely has active TB disease Consider submitting another specimen for NAAT to verifyPresumed to have TB if two or more specimens are NAAT positiveUse clinical judgment to determine whether to start treatment, start contact investigation and place on isolation.Confirm by culture result
14Smear-, NAAT- For smear- specimens, sensitivity is low Diagnosis of TB cannot be excludedRely on clinical judgmentRequesting a second NAAT may be helpfulContact investigation may be delayed and patient considered non-infectious if sputum smear- x 2 and all NAAT results are negative.Confirm by culture result
15Inhibited NAATAmplification was inhibited due to a naturally occurring inhibitor in the specimen or processing reagent (example: blood).Can result in a false negativeTest for inhibitors will be automatically run by lab on all smear+, NAAT- specimensIf present, lab will contact you for additional specimen to test
17ConclusionNAAT will provide LHDs with additional information to base decisions uponLHDs will not need to do anything different when collecting sputum to rule out TBDo not use NAAT if the patient has been on TB meds. for more than 7 days or was treated within last yearThe TB Program is available to assist with interpretation of results!