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Investigating tuberculosis (TB) in someone who is already on steroids needs extra care because steroids suppress the immune system and can mask typical test results.
⚠️ Why steroids matter
Steroids (e.g. Prednisolone) can:
Suppress immune response
Reduce inflammation → fewer symptoms
Cause false-negative TB tests (especially skin tests)
🧪 Key Investigations for TB (on steroids)
1. Interferon-Gamma Release Assay (IGRA)
Blood test (e.g. QuantiFERON-TB Gold)
Preferred over skin test in immunosuppressed patients
✅ Pros:
Not affected by BCG vaccination
More reliable than skin test on steroids
⚠️ Limitation:
Can still be falsely negative if immunosuppression is severe
2. Tuberculin Skin Test (TST)
Also called Mantoux test
⚠️ On steroids:
May be false negative (anergy)
Less reliable → not preferred alone
3. Chest Imaging
Start with Chest X-ray
If unclear → CT chest
Looking for:
Cavitation
Upper lobe infiltrates
Miliary pattern
4. Microbiological Tests (Most Important for active TB)
Sputum tests:
AFB smear microscopy
Culture (gold standard)
PCR test (e.g. GeneXpert MTB/RIF)
✅ These are NOT affected by steroids
👉 Essential if active TB suspected
5. Site-specific tests
If extrapulmonary TB suspected:
Lymph node biopsy
Pleural fluid analysis
Adrenal imaging (CT/MRI) if adrenal TB suspected
🧠 Practical Approach (Exam Style)
If patient is on steroids:
Do IGRA
Do chest X-ray
If symptoms → send sputum for GeneXpert + culture
Don’t rely on Mantoux alone
⚠️ Important Clinical Point
Always rule out TB before starting long-term steroids if possible
If already on steroids and TB suspected → investigate aggressively
🔑 Quick Summary
IGRA > Mantoux in steroid patients
Microbiology (GeneXpert/culture) = most reliable
Imaging supports diagnosis
False negatives are common → interpret cautiously
If you want, I can give you a step-by-step clinical algorithm or OSCE-style answer for this scenario.
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