Isoniazid (Serum/Plasma Concentration) with Quantitative Confirmation
This test measures the amount of isoniazid, an antibiotic used to treat tuberculosis, in your blood. It helps determine if your medication levels are within safe and effective ranges.
["This test ensures your tuberculosis treatment is working properly and avoids potential side effects from too much or too little medication."]
Key facts at a glance
- LOINC
- 25218-9
- Short code
- Isoniazid Islt Slgr Mcbct AB 0.2
- Synonyms
- Isoniazid Islt Slgr Mcbct AB 0.2
- Category
- chemistry
- Sample
- serum
- Container
- Red-top tube (SST)
- Units
- N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- Method
- method-for-slow-growing-mycobacteria-antibiotic-concentration-at-ug-ml
- Specimen volume
- 5 mL
- Stability
- Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
- Hemolysis max
- 500
- Lipemia max
- 1000
- Icterus max
- 500
- TAT
- 4–24 hours
- Order
- routine
Why This Test Is Done
Your healthcare provider may order this test if you’re taking isoniazid for tuberculosis treatment. It helps monitor whether your dose is appropriate and if your body is processing the medication correctly. This is especially important for long-term treatment to prevent resistance or toxicity.
What to Expect Before the Test
No special preparation is needed. You may have a small needle inserted into a vein (usually in your arm) to draw blood. If you’re on long-term treatment, your provider may check levels periodically to adjust your dose if needed.
What the Test Results Mean
Results are used to confirm if your isoniazid levels are therapeutic (safe and effective). Low levels may indicate the medication isn’t working as intended, while high levels could signal potential side effects like liver damage.
Common Reasons for Testing
This test is often done during tuberculosis treatment to prevent resistance, optimize dosing, or detect side effects early. It’s particularly important for patients with HIV, those on other medications affecting isoniazid metabolism, or those with liver concerns.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Clinical Significance
Short name
Isoniazid Level (Serum/Plasma)
Frequently asked questions
Why might my doctor want to check my isoniazid levels?
What happens if my isoniazid levels are too high or too low?
How often should I get this test?
Sources
- 1
- 2Lab Tests OnlineSource
- 3
Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.
This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
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