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Ethambutol Quantitative Drug Level (Serum)

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

This test measures the amount of ethambutol, a medication used to treat tuberculosis, in your blood. It helps doctors monitor your dose and ensure it stays within safe levels.

Quick summary

["This test helps ensure your tuberculosis treatment is effective and safe by checking your blood levels of ethambutol."]

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

Key facts at a glance

LOINC
20381-0
Short code
Ethambutol Islt SlowMyco
Synonyms
Ethambutol Islt SlowMyco
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
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 ethambutol to treat tuberculosis. It helps them check whether your dose is appropriate and whether the medication is working properly. This is especially important because too much or too little can affect your health.

What to Expect Before the Test

No special preparation is needed for this blood test. You may have a small needle inserted into your arm to draw a blood sample. The process usually takes a few minutes, and you can resume normal activities afterward.

What the Test Results Mean

Results are used to guide your treatment. Low levels might mean your dose needs to be increased, while very high levels could require a dose adjustment or temporary pause in treatment. Your doctor will discuss these findings with you.

Common Reasons for Testing

Doctors test for ethambutol levels to prevent side effects like vision problems (which can occur at high doses) and to ensure the medication is working effectively against tuberculosis.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Ethambutol levels help prevent toxicity (such as optic neuritis, which can cause vision loss) and ensure adequate drug exposure to treat tuberculosis. Regular monitoring is critical for patients on long-term therapy, as levels may fluctuate over time.

Short name

Ethambutol Level

Frequently asked questions

What happens if my ethambutol level is too high?
High levels may increase the risk of side effects like vision changes or kidney issues. Your doctor will adjust your dose or monitor you closely until levels return to a safe range.
Can I eat or drink before this test?
You can eat and drink normally before this test, as it’s a simple blood draw with no dietary restrictions.
How often will I need this test?
Your doctor will determine the frequency based on your treatment plan, but it may be done every few weeks or months during active therapy.
  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