How is gastric lavage performed for obtaining respiratory specimens in children suspected of pulmonary tuberculosis, what are its indications and contraindications, and how does its diagnostic yield compare to induced sputum?

Gastric Lavage for Pediatric Tuberculosis Diagnosis

Technique and Procedure

Gastric lavage (gastric aspirate) involves intubating the stomach after an overnight fast to collect swallowed sputum before the stomach empties, and should be performed on 3 consecutive mornings for optimal diagnostic yield. 1

Collection Protocol

• Perform the procedure early in the morning after overnight fast to capture respiratory secretions that have been swallowed during sleep and accumulated in the stomach overnight 1, 2

• Collect specimens on 3 consecutive mornings rather than a single collection, as this provides diagnostic yields of 40-50% overall 1, 3

• Meticulous attention to collection technique is critical - standardized protocols including strict timing, base neutralization of aspirate specimens, and expedited processing can improve yield from 8% to 50% 1, 4

• The first gastric aspirate has the highest yield, so if only one specimen can be obtained, prioritize the first morning collection 1

Indications for Gastric Lavage

Gastric lavage is indicated for all children suspected of pulmonary tuberculosis who cannot spontaneously produce sputum, particularly infants and young children. 1

High-Priority Populations

• Infants have the highest diagnostic yield (up to 90%) and should always undergo specimen collection 1, 3

• Children with extensive or symptomatic disease achieve yields up to 77% 1

• Immunocompromised children require respiratory specimens regardless of contact investigation findings 1, 3

• Children with suspected drug-resistant TB exposure need microbiological confirmation because 2-15% have susceptibility patterns differing from the presumed source case 1, 3

Exceptions Where Collection May Be Deferred

• Children with uncomplicated pulmonary TB identified through recent contact investigation where the source case has confirmed pan-susceptible TB may not require microbiological confirmation in low-incidence settings 1

• This exception should NOT apply to infants, immunocompromised hosts, or children with extensive/disseminated disease 1, 3

Contraindications and Safety

Gastric lavage is generally safe with minimal contraindications in pediatric patients. 1

• The procedure is well-tolerated in children of all ages, including infants as young as 1 month 5, 6

• No absolute contraindications are specified in major guidelines, though standard precautions for nasogastric intubation apply 1

Diagnostic Yield Comparison: Gastric Lavage vs. Induced Sputum

Gastric lavage provides superior diagnostic yield compared to induced sputum in most pediatric populations, though recent evidence suggests induced sputum may be comparable or superior in high HIV-prevalence settings. 7, 5

Comparative Diagnostic Yields

• Gastric lavage: 32-50% overall yield when performed on 3 consecutive mornings 1, 7, 8

  • Up to 90% in infants 1
  • Up to 77% in children with extensive disease 1

• Induced sputum: 20-30% yield with nasopharyngeal aspiration or sputum induction with bronchodilator 1

• Bronchoalveolar lavage (BAL): 10-22% yield, making it the least effective option 1

Evidence Divergence: Traditional vs. High HIV-Prevalence Settings

There is important divergence in the evidence based on geographic setting and HIV prevalence:

• Traditional evidence (low HIV-prevalence) from multiple studies shows gastric lavage superior to both BAL and induced sputum 7, 8

  • One study found gastric lavage positive in 32% vs. BAL in 12% 7
  • Another found gastric lavage positive in 50% vs. BAL in 10% 8

• High-quality evidence from high HIV-prevalence settings shows induced sputum may be superior 5

  • A 2005 Lancet study of 250 children in South Africa found induced sputum positive in 87% vs. gastric lavage in 65% (difference 5.6%, p=0.018) 5
  • One induced sputum sample had similar yield to three gastric lavages in this setting 5
  • Results were consistent in both HIV-infected and HIV-uninfected children 5

• European evidence suggests comparable yields when both techniques are optimized 6

  • A Spanish study found gastric lavage positive in 47.1% vs. induced sputum in 41.2% 6

Practical Recommendation Algorithm

The American Thoracic Society/CDC guidelines state there is insufficient evidence to advocate one collection method over another, but provide the following framework: 1

1. In resource-limited or high HIV-prevalence settings: Consider induced sputum as first-line, as it may be more convenient and equally or more effective 5, 6

2. In low HIV-prevalence developed countries: Gastric lavage on 3 consecutive mornings remains the traditional standard 1, 7, 8

3. Optimal approach: Combine both methods when feasible, as this increases overall diagnostic yield to the highest levels 6

4. Reserve BAL for complicated cases or when other methods fail, given its lower yield 1, 3

Critical Processing Requirements

All respiratory specimens must undergo simultaneous testing with multiple modalities to maximize diagnostic yield. 3, 2

• Send every specimen for AFB smear microscopy, mycobacterial culture, and Xpert MTB/RIF testing 3, 2

• Use only FDA-approved Xpert MTB/RIF assay in the United States 1, 3

• Expedited processing is essential - delays significantly reduce culture yield 1, 4

• All molecular resistance results must be confirmed by phenotypic drug susceptibility testing via liquid culture per international guidelines 3

Common Pitfalls to Avoid

• Collecting only one gastric aspirate - this significantly reduces yield compared to 3 consecutive morning collections 1, 2

• Poor timing of collection - specimens must be collected early morning after overnight fast, not at random times 2, 4

• Delayed processing - gastric aspirates must be neutralized and processed expeditiously 4

• Assuming source case susceptibility applies to the child - up to 15% of children have different susceptibility patterns 1

• Relying solely on one collection method - combining gastric lavage with induced sputum increases overall diagnostic yield 6