What do these lab results mean?Context for the TB Case Manager

PART 1: Smear Microscopy and NAATJen Miller, RN

MT DPHHS Communicable Disease Epidemiology

Diagnosing Pulmonary TB DiseaseHigh resource settings

• Medical history• Physical exam• Imaging (chest X-ray, CT, other)• Sputum examinations– Smear microscopy– Culture– Nucleic acid amplification testing– Drug susceptibility testing – Genotyping

2

Whole genome sequencing

PyrosequencinggyrA mutation in codon 94

What to expect when they are expectorating.

This Photo by Unknown Author is licensed under CC BY-SA-NC

Learning Objectives

By the end of the training, you will be able to:• describe 4 TB diagnostic tests and list several features

unique to each one• interpret sample laboratory test results, and determine

next steps the nurse case manager should take

4

Polling Question 1

A positive diagnostic acid-fast bacilli (AFB) smear result helps to…

a. Determine whether someone has active tuberculosis or notb. Inform about the potential infectiousness of a patientc. Determine the likelihood drug resistance is presentd. I’m not really sure

What do the numbers mean?

Number of AFB foundFluorescent Microscopy250x 450x

Reported as

0 0 No AFB seen

1-2 /30 fields 1-2 /70 fields Exact count*

1-9/10 fields 2-18/50 fields 1+

1-9/ field 4-36/10 fields 2+

10-90/field 4-36/field 3+

>90/field >36/field 4+

*Recommend repeat specimen

Rare

Few

Moderate

Many

Characteristics of the TB organism

• Slightly curved, rod shaped bacilli• 0.2 - 0.5 microns in diameter;

2 - 4 microns in length• Thick lipid cell wall• Acid fast bacilli (AFB) - resists

decolorization with acid alcohol– Other non-tuberculous mycobacteria

(NTM) also have this characteristic

• Multiplies slowly (~ every 18-24 hours)– Samples can become overgrown with

other, faster replicating organisms

Source: CDC/ Dr. George P. Kubica, 1979

7Source: Grace Lin, CDPH/MDL

Zeihl-Neelsen (ZN) stain

Auramine-rhodamine (AR)

Getting a Quality Sputum Specimen

• Coach on techniques for getting a deep coughed sample

• Well-ventilated space• First morning specimen = BEST• Sterile, single-use container– Ensure lid is secured– Well labeled (include specimen type)– Send to lab as soon as possible– Refrigerate if transport to lab is

delayed

• Look at the specimen– Mucus plugs (mucopurulent)– Shoot for 5 ml – 10 ml (min 2ml)

• Consider sputum induction when patient unable to spontaneously produce good quality specimen

• Diagnostic samples = 3, at least 8 hours apart

AFB Smear results also used for…

Prioritizing TB Contact InvestigationSputum AFB smear-positive cases are higher priority for initiation of contact investigation

Monitoring Clinical Response to TB TreatmentWatching for improving sputum AFB smear microscopy results and eventual conversion to smear negative

Determining End of Airborne IsolationThree negative AFB smears along with clinical improvement and appropriate treatment for > 2 weeks

Polling Question 2If the initial diagnostic sputum AFB smear results are negative, we can breathe easy because it means the person EITHER does not have TB, OR that s/he is not infectious.a. Trueb. Falsec. Not sure

Nucleic acid amplification test (NAAT)

• The NAAT is a molecular test.• It detects genetic materials of TB (not antibodies or

antigens).• CDC recommends use of NAATs in all patients for

whom a TB diagnosis is being considered if the results could influence clinical or public health decision-making.

• The reality…most labs only automatically test smear+ sputum or upon request due to expense. GeneXpert can be requested for up to 7 days after sputum processed.

• Most labs are not validated (approved ) to test primary extrapulmonary specimens (e.g. tissue, lymph node, etc.) using NAAT. Only respiratory specimens.

Nucleic acid amplification test (NAAT)

• NAAT for MTB = TB PCR, GeneXpert MTB/RIF, MTD, other names or types• Validated for sputum and respiratory specimens (washings), does this

mean you ignore tissue analysis positives?• Rule in or rule out MTB - faster release from airborne or home isolation

(if NTM) or earlier start of appropriate treatment • May be used to detect MTB faster when smear negative = less spread of

TB disease due to earlier initiation of airborne isolation and treatment

Nucleic acid amplification test (NAAT) continued...

• Results available quickly in <24 hours - 5 days after sputum submitted.• Do NOT use as “test of cure” (dead bugs). • If positive, is a confirmed TB case

– Though this meets case definition, it doesn’t mean you’re done monitoring the laboratory results!

PatientFamily

Friends

Provider

Public health

Nursing staff

Don’t forget communications that need to occur!

Remember that the patient may have a large circle that would be affected by the findings. Don’t forget to communicate with partners and to provide contact information for your agency in case questions arise.

Helpful Lab Resources for the Case Manager

https://www.heartlandntbc.org/products/https://www.aphl.org/programs/infectious_disease/tuberculosis/Pages/Training-Modules.aspx

Sputum Collection – Patient Instructional Videos:https://www.youtube.com/watch?v=rIQDP41Qd8shttps://www.youtube.com/watch?v=Vs9DWzuvXUchttps://www.youtube.com/watch?v=92dT_1kbbek

Breakout Practice Instructions: PART 1• Small group facilitated discussion• Video cam on for introductions at

the start• Use Learner Packet to record

discussion points• If audio problems or technical

assistance needed, select blue “LEAVE” button, bottom right, then “LEAVE BREAKOUT”üTake note of breakout room number