Diagnosis of Tuberculosis in Children — Diagnostic Algorithm

Introduction

STEP 1 — History & Clinical Evaluation

A. Epidemiological Risk Factors

• Contact history: Close contact with sputum-positive (smear/culture positive) adult TB case — most important clue in children
• Age < 5 years: highest risk of progression from infection to disease
• HIV infection / malnutrition / immunocompromised state
• Unvaccinated with BCG or BCG failure

B. Symptoms (Constitutional — persistent ≥ 2–3 weeks)

C. Extrapulmonary Clues

• Cervical lymphadenopathy — matted nodes > 2×2 cm
• TB meningitis — most common in children < 3 years (Harrison's, p. 5252)
• Cold abscess, gibbus deformity (Pott's spine)
• Abdominal distension, hepatosplenomegaly

STEP 2 — Tuberculin Skin Test (Mantoux Test)

• Antigen: 2 TU of PPD RT-23 / 5 TU PPD-S injected intradermally on volar aspect of forearm
• Read at 48–72 hours — measure induration (not erythema) in mm

Interpretation (IAP / Revised National TB Programme Guidelines):

Key point: BCG vaccination can cause cross-reactivity and false positives. IGRAs (Interferon-Gamma Release Assays) like QuantiFERON-TB Gold / T-SPOT are unaffected by BCG.

STEP 3 — Radiological Evaluation

Chest X-Ray (PA View) — First-line Imaging

1. Hilar / paratracheal lymphadenopathy — hallmark of primary TB
2. Ghon focus — peripheral parenchymal opacity
3. Ghon complex = Ghon focus + hilar lymphadenopathy
4. Segmental collapse / consolidation (due to airway compression by nodes)
5. Miliary pattern — 1–2 mm diffuse nodules (miliary TB)
6. Pleural effusion
7. Cavitation — rare in young children; seen in adolescents (adult-type TB)

CT Chest / HRCT

• More sensitive for mediastinal lymphadenopathy and subtle parenchymal disease
• Indicated when CXR is normal but clinical suspicion is high

STEP 4 — Microbiological Investigations

A. Specimen Collection in Children

• Older children (> 6 years): Sputum (3 specimens — early morning preferred; minimum 3 mL, optimal 5–10 mL)
• Younger children (< 6 years): Unable to expectorate — use:
  • Gastric aspirate (early morning, fasting × 3 days) — gold standard specimen in young children
  • Induced sputum (using hypertonic saline nebulization)
  • Nasopharyngeal aspirate
  • Bronchoalveolar lavage (BAL) — if above unavailable

B. Tests on Specimen

STEP 5 — Additional Investigations

STEP 6 — Diagnostic Scoring (When Bacteriological Confirmation is Unavailable)

IAP Revised Scoring System for Childhood TB:

STEP 7 — Therapeutic Trial

• If score borderline (4–5), or diagnosis uncertain → 2-week trial of broad-spectrum antibiotics (to exclude bacterial pneumonia)
• If no improvement → therapeutic trial of ATT (monitored for 4–8 weeks)
• Response to ATT (weight gain, fever resolution) supports the diagnosis

STEP 8 — Final Classification

Summary Algorithm (Flowchart)

Child with Suspected TB
         ↓
Step 1: History — Contact, Symptoms ≥ 2 weeks, Risk Factors
         ↓
Step 2: Mantoux Test (TST) / IGRA
         ↓
Step 3: Chest X-Ray (Hilar adenopathy, Ghon complex, Miliary pattern)
         ↓
Step 4: Microbiological Specimens
     ├─ Sputum / Gastric aspirate
     ├─ AFB Smear + Culture (Liquid + Solid)
     └─ CBNAAT / GeneXpert MTB/RIF ← FIRST LINE NAAT
         ↓
Step 5: Additional Workup (CBC, ESR, CSF, FNAC, IGRA as indicated)
         ↓
Step 6: Apply IAP Scoring System
     Score ≥ 6 → Start ATT
     Score 4–5 → Antibiotic trial → No response → Start ATT
         ↓
Step 7: Monitor Response to ATT (Therapeutic confirmation)

Key Points for Exam

1. Paucibacillary disease makes microbiological confirmation difficult in children
2. Gastric aspirate × 3 days is the specimen of choice in children < 6 years
3. CBNAAT (GeneXpert) is the first-line NAAT endorsed by NTEP India
4. Mantoux ≥ 10 mm is positive in immunocompetent children; ≥ 5 mm in immunocompromised
5. Hilar lymphadenopathy on CXR is the hallmark of primary TB in children
6. IAP score ≥ 6 → initiate ATT even without bacteriological confirmation
7. BCG vaccination does NOT affect IGRA results
8. TBM is most common in children < 3 years
9. Therapeutic trial of ATT is a valid diagnostic tool when all else fails
10. Always rule out MDR-TB (using LPA / DST) in contacts of MDR-TB cases