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Isoniazid (Serum) Concentration, Quantitative

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

This test measures the amount of isoniazid, a medication used to treat tuberculosis, in your blood. It helps doctors check if your dose is working properly.

Quick summary

["This test helps ensure your tuberculosis treatment is effective and safe."]

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

Key facts at a glance

LOINC
25217-1
Short code
Isoniazid Islt Slgr Mcbct AB 0.1
Synonyms
Isoniazid Islt Slgr Mcbct AB 0.1
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 Is This Test Done?

Your healthcare provider may order this test if you’re taking isoniazid to treat tuberculosis (TB) or prevent it. It’s often done during treatment to monitor levels and adjust your dose if needed.

What to Expect Before the Test

No special preparation is needed. You’ll have a small needle inserted into your arm to draw blood. It usually takes a few minutes, and you may feel a brief pinch.

What the Results Mean

Results help determine if your isoniazid levels are within the right range for your treatment. Too little or too much can affect how well the drug works or cause side effects.

Common Reasons for Testing

Doctors may check isoniazid levels if you’re on long-term treatment, if you have side effects (like nausea or liver concerns), or if you’re taking other medications that could interact with it.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance: Monitoring Treatment and Safety

Short name

Isoniazid Level

Frequently asked questions

How often should I expect this test?
Your doctor will decide based on your treatment plan. Some patients get it weekly or monthly, while others may need it less often.
What if my results are outside the normal range?
If levels are too low, your dose may need to be increased. If levels are too high, your doctor might adjust your medication or monitor you closely for side effects.
Can I eat or drink before this test?
You can eat and drink normally, but avoid alcohol for 24 hours before the test, as it may affect results.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

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.

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