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Bacterialkatgdrugresmutisltspm

Published: August 9, 2026Updated: August 16, 2026

This test detects genetic mutations in the katG gene of bacteria, primarily used to identify isoniazid resistance in tuberculosis treatment.

Quick summary

{"Detects genetic mutations that cause resistance to isoniazid, a key tuberculosis medication","Performed using molecular methods on serum sample","Results help doctors choose effective antibiotics for treatment","Important for managing drug-resistant tuberculosis"}

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
94054-4
Short code
TBKATG
Synonyms
Bacterial katG drug res mut Islt/Spm
Category
chemistry
Sample
serum
Container
Sterile, leak-proof container for sputum or respiratory specimens; sterile collection tube for serum/plasma; specific molecular transport medium as recommended by testing laboratory.
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
molgen
CPT
87556
SNOMED
434821002
Specimen volume
Variable by specimen type: Sputum 1-5 mL; Serum 1-3 mL; Bronchoalveolar lavage (BAL) 10-30 mL; Tissue biopsy minimum 1 cm³. Consult laboratory-specific requirements.
Stability
Serum: 2-8°C for 24 hours, -70°C for long-term storage. Sputum/clinical specimens: Refrigerated (2-8°C) for up to 7 days; frozen at -70°C for extended storage. Avoid repeated freeze-thaw cycles. DNA extracts stable at -20°C to -80°C for extended periods.
Hemolysis max
500
Lipemia max
1000
Icterus max
500
TAT
24–168 hours
Order
routine

What is this test?

The katG gene drug resistance test is a molecular test that detects specific genetic mutations in the katG gene of bacteria, primarily Mycobacterium tuberculosis (the bacteria that causes tuberculosis). These mutations are associated with resistance to isoniazid (INH), one of the most important first-line antibiotics used to treat tuberculosis.

Why is it important?

Isoniazid is a cornerstone medication in tuberculosis treatment. When the katG gene mutates, particularly at position 315 (S315T mutation), the bacteria become resistant to isoniazid. This test helps doctors quickly identify whether the tuberculosis infection is resistant to this important drug, allowing them to adjust treatment plans promptly.

How is the test performed?

A serum sample is collected from the patient. Laboratory technicians then use molecular methods (such as PCR or gene sequencing) to analyze the katG gene for specific mutations known to cause drug resistance. The test looks for the presence of these mutations rather than culturing the bacteria.

What do the results mean?

If mutations are detected (positive result), it indicates that the tuberculosis bacteria are likely resistant to isoniazid. If no mutations are found (negative result), the bacteria are likely still sensitive to isoniazid. This information is crucial for healthcare providers to design an effective treatment regimen.

Reference range

Not Applicable - Qualitative/Presence-Absence molecular test. Results reported as: 'Mutation Detected' (isoniazid resistance predicted) or 'Mutation Not Detected' (isoniazid susceptibility predicted). The most clinically significant mutation detected is katG S315T, conferring high-level isoniazid resistance.N/A

Specimen: serum

No special patient preparation required. However, specimen should be collected prior to initiation of anti-tuberculosis therapy when possible to avoid false-negative results. Informed consent may be required for genetic/molecular testing per institutional policy.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Frequently asked questions

Who needs this test?
This test is typically ordered for patients diagnosed with tuberculosis, especially in areas where drug-resistant TB is common, or when there is concern that standard treatment is not working. It may also be performed as part of initial TB drug susceptibility testing in high-risk populations.
How long does it take to get results?
Unlike traditional culture-based tests that can take weeks, molecular tests like this one typically provide results within a few days to a week, allowing for faster treatment adjustments.
Does a positive result mean I cannot be cured?
No, a positive result for katG mutations means that isoniazid will not be effective, but there are other antibiotics available to treat drug-resistant tuberculosis. Your healthcare provider will design an alternative treatment plan based on the results.
Is the test painful?
The test requires a blood draw, which may cause brief discomfort similar to any standard blood test. The procedure is generally well-tolerated.
Do I need to prepare for the test?
No special preparation is typically required. You should inform your healthcare provider about any medications you are taking, as they may affect the test or its interpretation.
  1. 1
    CDC - Tuberculosis (TB)Source
  2. 2
    WHO - Drug-resistant tuberculosisSource
  3. 3
    LOINC Code 94054-4Source

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This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy