Sputum collection is an important tool in the evaluation of patients with suspected active TB. Assessment for active TB should take into account multiple factors before proceeding to sputum collection, including epidemiologic and medical risk factors, symptoms, and radiographic abnormalities.
Features that suggest concern for active TB include the presence of:
- Risk factors (non-US-born, immunocompromised, or known lifetime exposure to active TB);
- Symptoms (can be varied, but typical symptoms may include > 3 weeks of cough, fever, chills, night sweats and/or weight loss); and
- Chest imaging concerning for active TB per radiology report
The California Department of Public Health TB Risk Assessment is a useful tool to help evaluate risk factors, available here.
The SFDPH TB Clinic does not see patients referred solely for the purpose of sputum induction. SFDPH TB Clinic will see patients with concern for possible active TB; a TB Clinic provider will review and assess whether sputa collection (including one induced sputa) is indicated. TB Clinic provider visits are available by appointment only. For referral information, click here.
For patients who do not meet the above criteria and have lower suspicion based on risk factors, clinical presentation and/or chest imaging, we may recommend the following evaluation be performed by you:
- Draw TST (US born patients) or Interferon gamma release assay (IGRA)(preferred)
- Collection of 3 expectorated morning sputa to send for AFB smear and culture, and one morning sputa sent for GeneXpert(MTB PCR)
Expectorated sputum can be collected safely in the home. Collection of sputa in the home may provide the same sensitivity and specificity as sputum induction. Evaluation of suspect TB patients at SFDPH TB Clinic includes one induced sputum and two home-collected morning sputa; we have found that collection of first-morning sputa can have similar or better yield than induced sputa collected later in the day. Check with your lab for any special instructions on sputum collection.
We recommend reviewing instructions with the patient in your clinic and providing them with:
- Home instructions in their preferred language from the link above
- Sputum cups x 3
- Biohazard bag for cups
- Lab slip (if needed by the patient)
A good example of an instructional video for patients on how to collect sputa can be found here.
Depending on the individual patient, a positive AFB smear may indicate TB or non-tuberculous mycobacterium. For positive results by AFB smear (particularly in patients where clinical or radiographic suspicion is low for non-tuberculous mycobacterium), GeneXpert, or culture, please contact us immediately at (628) 206-8524.
For more detailed information, a helpful resource for recommendations on TB diagnostic testing is available here.