What this test measures
This test determines whether a cultured M. tuberculosis isolate is sensitive or resistant to pyrazinamide (PZA, Z) at the WHO-defined critical concentration. Pyrazinamide is unique — it acts only at acidic pH, killing slowly metabolising bacilli that other drugs cannot reach. Its sterilising activity is the reason TB therapy was shortened from 9 to 6 months.
Phenotypic pyrazinamide DST is technically demanding because of the acidic pH requirement, and MGIT-based PZA testing is the preferred phenotypic method. Resistance is mediated by mutations in the pncA gene; molecular pncA sequencing is a useful complement and increasingly preferred.
Why it matters
Pyrazinamide is part of the 2-month intensive phase of standard 6-month TB therapy (HRZE). Resistance can extend treatment duration in drug-sensitive TB and alters regimen choice in MDR-TB. WHO data show rising pyrazinamide resistance globally, particularly among MDR-TB isolates.
Pyrazinamide is also part of the BPaLM regimen variants for MDR-TB, making confirmation of susceptibility relevant to modern all-oral regimens too.
How to prepare
A positive M. tuberculosis culture (MGIT) is required. If not available, sputum samples must be collected for AFB culture first.
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.
Pyrazinamide — why it matters
| Property | Significance |
|---|---|
| Sterilising activity | Kills slowly metabolising bacilli; enables 6-month therapy |
| Acidic-pH active | Works in granulomas and intracellular environment |
| Resistance gene | pncA — molecular testing increasingly used |
| Toxicity | Hepatitis, hyperuricaemia (gout flares) |
Frequently asked questions
Why is pyrazinamide so important?
It kills slowly metabolising mycobacteria in acidic environments (like granulomas) that other drugs cannot. This is why adding pyrazinamide allowed TB treatment to be shortened from 9 to 6 months.
Why is pyrazinamide DST tricky?
Pyrazinamide only works at low pH, which makes culture-based testing difficult. MGIT is the most reliable phenotypic method. Molecular pncA sequencing is increasingly used as a faster alternative.
What if I am pyrazinamide-resistant?
Treatment is extended (often to 9 months) in drug-sensitive TB. In MDR-TB the regimen is modified to compensate. Specialist input is essential.
What are the side effects?
Hepatitis (raised liver enzymes), hyperuricaemia which can trigger gout, joint aches, GI upset, and rash. Liver function and uric acid are monitored on treatment.
How long does the test take?
About 1–3 weeks from a positive culture; 4–6 weeks total from sputum collection.
Is the test available under NTEP?
Yes — at NTEP intermediate and national reference labs. Private NABL-accredited labs also offer it.
Why is pyrazinamide not in CBNAAT or LPA?
Until recently, no molecular test covered pyrazinamide. Newer assays (Xpert MTB/XDR, pncA sequencing) are now expanding molecular pyrazinamide testing.
Related Tuberculosis / Mycobacterial tests
Tests commonly ordered alongside ANTIBIOGRAM - MTB (PYRAZINAMIDE), 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
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