Skip to content

Isoniazid Drug Concentration in Serum

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

This test measures the amount of the antibiotic isoniazid in your blood serum to check if it’s working properly and at the right level.

Quick summary

["Isoniazid levels help ensure your treatment is effective and avoid potential side effects."]

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

Key facts at a glance

LOINC
42651-0
Short code
Isoniazid Islt Slgr Mcbct AB 5.0
Synonyms
Isoniazid Islt Slgr Mcbct AB 5.0
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 (INH) for tuberculosis (TB) treatment. It helps monitor whether the medication is reaching safe and effective levels in your blood, especially if you have kidney issues or take other medications that might affect how isoniazid works.

What to Expect Before the Test

No special preparation is needed. A blood sample will be taken from a vein in your arm by a healthcare professional. It may cause a slight pinch, but it usually doesn’t cause long-lasting discomfort.

What Does the Test Result Mean?

Results are typically reported as a concentration value (e.g., micrograms per milliliter). Your provider will interpret these results in relation to your medical condition, other medications, and lab reference ranges specific to your situation.

Common Reasons for Testing

This test is often done during TB treatment to confirm the drug is at an appropriate level. It may also be used if you have side effects (like nausea or liver issues) that could be linked to isoniazid.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Low levels may indicate the drug isn’t working well, requiring dose adjustments. High levels could signal toxicity, such as liver damage or nerve problems, prompting medical review. Regular monitoring helps balance effectiveness and safety.

Short name

Isoniazid Level

Frequently asked questions

When might I need this test?
You may need this test if you’re prescribed isoniazid for TB treatment, especially if you have kidney problems, take other medications, or experience unusual symptoms like nausea, vomiting, or fatigue.
How long does it take to get results?
Results are usually available within 1 to 3 business days, depending on your lab’s processing time.
Can I eat or drink before the test?
Yes, you can eat and drink normally before the test. No fasting is required.
  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