What this test measures
The SIRE panel is the classic first-line TB drug susceptibility test. It tests Mycobacterium tuberculosis grown on culture against the four core first-line drugs: Streptomycin (S), Isoniazid (H), Rifampicin (R), and Ethambutol (E). Results are reported as sensitive or resistant at WHO-defined critical concentrations.
For a drug-sensitive M. tuberculosis isolate, the standard 6-month regimen (2 months HRZE → 4 months HR) achieves over 95% cure rates. Resistance to any of these drugs — particularly to isoniazid (H) and rifampicin (R) — changes the regimen substantially.
Why it matters
India's NTEP uses molecular tests (CBNAAT, LPA) as the front-line screen for rifampicin and isoniazid resistance because they are fast. Phenotypic SIRE DST on MGIT or LJ culture remains the reference standard, especially when molecular and phenotypic results disagree, or when ethambutol and streptomycin status is required (CBNAAT/LPA do not cover these).
Isoniazid mono-resistance is increasingly common in India — affecting nearly 1 in 10 new TB cases according to drug resistance surveys. Identifying mono-resistance early lets clinicians swap to an effective regimen (typically replacing H with a fluoroquinolone) and avoid treatment failure.
How to prepare
A positive M. tuberculosis culture (MGIT or LJ) is required. If not yet available, sputum samples will need to be collected for AFB culture first. Inform the lab of any TB drug(s) already taken — even short courses can alter the phenotypic result.
Markers & reference ranges
Reference ranges below are typical adult values. Your lab's reported range may differ slightly based on the assay platform and patient demographics — always read your report against the range printed on it.
| Marker | Normal range | If low | If high |
|---|---|---|---|
| Streptomycin (S) (—)[1] | Sensitive | — | Resistant — streptomycin not usable. Streptomycin is rarely used in modern regimens, so isolated S resistance has limited treatment impact. |
| Isoniazid (H) (—)[1] | Sensitive | — | Resistant — isoniazid mono-resistance is increasingly common in India. WHO recommends a 6-month regimen of RZE + Levofloxacin (HrZE → HRZE-Lfx schedule varies; check NTEP guidance). |
| Rifampicin (R) (—)[1] | Sensitive | — | Resistant — single most important resistance finding in TB. Treated as MDR-TB (along with isoniazid resistance, which is usually present). Triggers PMDT MDR regimen. |
| Ethambutol (E) (—) | Sensitive | — | Resistant — ethambutol cannot be used. E resistance often co-occurs with H or R resistance and changes the regimen options. |
First-line resistance patterns
| Pattern | Regimen implication |
|---|---|
| All sensitive (S, H, R, E) | Standard 6-month regimen (HRZE → HR) |
| Isoniazid mono-resistant | RZE + Levofloxacin x 6 months (WHO H-mono regimen) |
| Rifampicin-resistant (RR) | Treated as MDR — PMDT regimen |
| MDR (H + R resistant) | Shorter or longer MDR regimen per PMDT |
| Streptomycin only | Standard HRZE → HR; no clinical impact |
Frequently asked questions
Why do CBNAAT if SIRE is more comprehensive?
CBNAAT gives a fast (2-hour) result for rifampicin resistance — critical for starting the right treatment immediately. Phenotypic SIRE takes 4–6 weeks but covers all four drugs and confirms molecular results.
My CBNAAT shows rifampicin resistance — do I still need SIRE?
Yes, ideally — SIRE confirms phenotypic resistance and clarifies isoniazid, ethambutol and streptomycin status, all of which are useful for designing the full MDR regimen.
How long does the result take?
About 1–2 weeks from a positive culture. Total time from sputum collection is typically 4–6 weeks. Molecular tests (CBNAAT / LPA) give same-week answers and are used in parallel.
Is SIRE DST done routinely in India?
It is done at NTEP intermediate and national reference labs for drug-resistant TB suspects, retreatment patients, and treatment failures. Private testing is also available.
What is isoniazid mono-resistance?
M. tuberculosis resistant to isoniazid but still sensitive to rifampicin. It is common in India and needs a modified 6-month regimen (RZE + Levofloxacin) rather than the standard HRZE.
How accurate is SIRE phenotypic DST?
For H, R, and E it is very reliable. For pyrazinamide (Z) — which is not in SIRE — phenotypic DST is technically difficult and often replaced by molecular testing.
Should I take this test if I am on TB treatment?
If you are responding well, no. If treatment is failing or you have relapse symptoms, yes — your doctor will order DST to look for new resistance.
Related Tuberculosis / Mycobacterial tests
Tests commonly ordered alongside AFB DRUG SUSCEPTIBILITY (SIRE) 1ST LINE, or that help interpret an unexpected result.
Sources & references
- WHO Consolidated Guidelines on Drug-Resistant TB · accessed 2026-05-30T00:00:00.000Z
- NTEP PMDT Guidelines · accessed 2026-05-30T00:00:00.000Z
- India TB Report 2024 · accessed 2026-05-30T00:00:00.000Z
- CDC — TB Drug Susceptibility · accessed 2026-05-30T00:00:00.000Z
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