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Theophylline Concentration (Serum/Plasma)

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

This test measures the amount of theophylline, a medication derived from tea leaves, in your blood. Theophylline is used to treat breathing problems like asthma or chronic obstructive pulmonary disease (COPD).

Quick summary

["Your doctor may order this test to check if your theophylline level is within the safe range for your treatment."]

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

Key facts at a glance

LOINC
33323-7
Short code
Theophylline Ur Ql Scn
Synonyms
Theophylline Ur Ql Scn
Category
chemistry
Sample
urine
Container
Sterile urine container
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
Method
screen
Specimen volume
10 mL
Stability
Room temperature: 2h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
0
Lipemia max
0
Icterus max
0
TAT
4–24 hours
Order
routine

Why Is This Test Done?

Your healthcare provider may request this test if you’re taking theophylline to manage breathing issues. They might also order it to monitor your dose, especially if you’re taking other medications that could affect how theophylline works in your body.

What Does the Test Measure?

Theophylline is a bronchodilator that helps open airways in your lungs. This test checks how much theophylline is present in your bloodstream, which can help ensure you’re getting the right amount for your condition.

How Is the Test Performed?

A blood sample is taken from a vein in your arm. The sample is then sent to a lab where it is analyzed using a sensitive method to measure the theophylline concentration.

What Are Common Results?

There are no specific reference ranges provided here since they can vary based on your medication dose, health status, and other factors. Your results will be interpreted by your healthcare provider in the context of your treatment plan.

Reference range

Therapeutic: 10-20 mcg/mLN/A

Specimen: urine

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

What happens if my theophylline level is too high?
If your level is too high, your doctor may reduce your dose or temporarily stop the medication to prevent serious side effects. They’ll monitor you closely until the levels return to a safe range.
Can food or other medications affect this test?
Yes, certain foods, like caffeine, and other medications can change how theophylline works in your body. Always tell your doctor about all medications, supplements, or foods you’re taking to avoid interactions.
How often should I get this test?
Your doctor will determine how often you need this test based on your treatment plan, how well your symptoms are controlled, and whether you’re taking other medications that interact with theophylline.
  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