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Theophylline Concentration (Serum/Plasma)

Published: August 9, 2026Updated: August 17, 2026

This test measures the amount of theophylline, a medication used to treat breathing problems like asthma or chronic obstructive pulmonary disease (COPD). It helps ensure your dose is safe and effective.

Quick summary

["This test checks your blood levels of theophylline to prevent overdose or underdose."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 17, 2026Editorial policy

Key facts at a glance

LOINC
14915-3
Short code
Theophylline SerPl-sCnc
Synonyms
Theophylline SerPl-sCnc
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Ref low
10
Ref high
20
Critical range
— – 20 N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
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 theophylline (a bronchodilator) to manage breathing issues. They may also check it if you’re experiencing side effects like rapid heartbeat, nausea, or trouble sleeping, or if you’re adjusting your medication dose.

How the Test Works

A blood sample is taken from a vein in your arm. The sample is then analyzed using a specialized lab technique to measure the amount of theophylline in your blood.

What to Expect Before the Test

No special preparation is usually needed, but let your provider know if you’re taking other medications or have any health conditions that might affect results.

Possible Side Effects or Risks

Blood tests are generally safe, but drawing blood can cause mild discomfort or bruising at the site. Rarely, there may be reactions to the needle or infection at the injection site.

Reference range

Therapeutic: 10-20 mcg/mLN/A

Specimen: serum

No special preparation usually required. Stay well hydrated. Inform your healthcare provider of all medications and supplements you are taking.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Theophylline Level

Frequently asked questions

How often should I get this test?
Your provider will determine the timing based on your medication schedule and symptoms. Typically, it’s done when you first start the medication or if your dose changes.
What do my results mean?
Results are compared to your specific dose and symptoms. Your provider will discuss them with you, as reference ranges can vary based on your health and medication.
Can I avoid this test?
No, this test is important for managing theophylline safely. Skipping it could increase risks of overdose or ineffective treatment.
  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 17, 2026. · Read our editorial policy