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Tuberculosis (TB) Diagnosis in Children — Structured Answer

(For PDU Medical College, Rajkot | Pediatrics University Practical/Theory Examination | 15 Marks)

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INTRODUCTION

• Paucibacillary nature of disease (especially <5 years)
• Difficulty in obtaining sputum samples
• Non-specific symptoms overlapping with other illnesses
• Microbiological confirmation achieved in only 15–50% of pediatric cases

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DIAGNOSTIC ALGORITHM — STEP BY STEP

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✦ STEP 1 — HISTORY & CLINICAL EVALUATION

A. Contact History

• Close contact with a sputum smear-positive TB case (especially household contact) is one of the strongest risk factors in children
• Duration, proximity, and smear status of the index case must be documented

B. Symptoms (Cardinal Features — Think "3 P's + 1 F")

Other features: night sweats, anorexia, failure to thrive, lymphadenopathy

C. Predisposing Factors

• Malnutrition (severe acute malnutrition = high risk)
• HIV infection
• Immunosuppressive therapy
• Unvaccinated status (no BCG)

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✦ STEP 2 — TUBERCULIN SKIN TEST (TST / MANTOUX TEST)

• Antigen: 2 TU of PPD-RT23 or 5 TU PPD-S injected intradermally on the volar aspect of the forearm
• Read at 48–72 hours — measure transverse induration (NOT erythema)

Interpretation in Children:

False Negatives (Anergy):

• Severe malnutrition, miliary TB, HIV, measles, steroid use, recent live viral vaccine, early disease

False Positives:

• BCG vaccination (usually <10 mm), NTM (Non-tuberculous mycobacteria) infection

Note: A positive TST indicates sensitization/infection, NOT necessarily active disease.

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✦ STEP 3 — CHEST X-RAY (CXR)

Characteristic Findings in Primary Childhood TB:

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✦ STEP 4 — MICROBIOLOGICAL CONFIRMATION

A. Sample Collection

B. Tests Performed on Samples

CBNAAT is recommended as the first-line diagnostic test under India's NTEP (National TB Elimination Programme) for all presumptive pediatric TB cases.

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✦ STEP 5 — IGRA (Interferon Gamma Release Assay)

• Tests: QuantiFERON-TB Gold Plus (QFT-Plus), T-SPOT.TB
• Measures IFN-γ release from T-cells sensitized to ESAT-6 and CFP-10 antigens
• Not affected by BCG vaccination — more specific than TST
• Limitations in children <5 years: higher indeterminate results; not routinely recommended for young children in India
• Used as adjunct to TST, not a replacement in most Indian settings

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✦ STEP 6 — ADDITIONAL INVESTIGATIONS

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✦ STEP 7 — SCORING SYSTEMS / DIAGNOSTIC SCORING

Indian Academy of Pediatrics (IAP) Diagnostic Score / WHO Symptom-Based Criteria

Score ≥6 → Probable TB → Start anti-TB treatment Score 3–5 → Possible TB → Investigate further / trial of ATT considered Score <3 → TB unlikely

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✦ STEP 8 — THERAPEUTIC DIAGNOSTIC TRIAL

• When microbiological confirmation is unavailable and score is borderline:
• Start 2-month trial of anti-TB therapy (HRZE)
• Positive response (weight gain, fever resolution, radiological improvement) supports diagnosis
• Widely practiced in India per NTEP guidelines for paucibacillary childhood TB

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FLOWCHART SUMMARY

Child with suspected TB
         ↓
History: Contact + Symptoms >2 weeks + Risk factors
         ↓
Mantoux Test + Chest X-ray (SIMULTANEOUSLY)
         ↓
  ┌──────────────────────┐
  │   CBNAAT / Sputum /  │
  │   Gastric aspirate   │
  └──────────────────────┘
         ↓
Microbiologically CONFIRMED?
   Yes → Start ATT (RNTCP/NTEP protocol)
   No  → Apply Diagnostic Score (IAP/WHO criteria)
         ↓
  Score ≥6 → Probable TB → Start ATT
  Score 3–5 → Additional tests (HRCT/IGRA/FNAC/Biopsy)
  Score <3  → Alternative diagnosis
         ↓
Always: HIV test + Baseline LFT + Drug sensitivity testing

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SPECIAL SITUATIONS

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IMPORTANT POINTS FOR VIVA

1. Gold standard for TB diagnosis = Culture on LJ medium
2. Rapid molecular test of choice in India = CBNAAT (Xpert MTB/RIF)
3. Most common CXR finding in childhood TB = Hilar lymphadenopathy
4. Confirmatory test for lymph node TB = FNAC / Biopsy — caseating granuloma with Langhans giant cells
5. Mantoux is read at 48–72 hours — induration, not erythema
6. BCG scar does not exclude TB; BCG-induced Mantoux reaction is usually <10 mm
7. ADA >40 U/L in pleural/CSF/ascitic fluid is supportive of TB
8. IGRA is not affected by BCG — preferred in BCG-vaccinated children when differentiating infection from BCG response

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REFERENCES

• Treatment of Drug-Susceptible Tuberculosis — WHO Guidelines (p. 29)
• Tuberculosis — NICE Clinical Guidelines (p. 26)
• IAP Standard Treatment Guidelines — Pediatric TB
• NTEP (National TB Elimination Programme) — India, 2023
• Nelson Textbook of Pediatrics, 21st Edition — Chapter on Tuberculosis
• WHO Operational Handbook on Tuberculosis — Module 2 (Diagnosis), 2022

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Examiner's Tip: For a 15-mark answer at PDU Medical College, cover at minimum — (i) clinical criteria, (ii) Mantoux interpretation, (iii) CXR findings, (iv) microbiological tests including CBNAAT, (v) diagnostic scoring, and (vi) special situations (TB+HIV / miliary TB). This answer covers all of them with appropriate depth.