Skip to content

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. It helps monitor your dose to ensure it’s effective for managing conditions like asthma or chronic obstructive pulmonary disease (COPD).

Quick summary

["This test helps doctors adjust your medication to avoid side effects or reduce the risk of overdose."]

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

Key facts at a glance

LOINC
35238-5
Short code
Theophylline SerPl-msCnc
Synonyms
Theophylline SerPl-msCnc
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 Is This Test Done?

Your healthcare provider may order this test if you’re taking theophylline or similar medications (like aminophylline) to treat breathing problems. Regular monitoring helps prevent low or high levels that could cause symptoms like headaches, rapid heart rate, or trouble breathing.

What to Expect Before the Test

No special preparation is needed. You’ll provide a blood sample, usually drawn from a vein in your arm. The process takes a few minutes, and you may feel a slight pinch. If you’re on a blood thinner, let your provider know before the test.

What the Results Mean

Results are compared to a general reference range for theophylline, but exact values can vary by lab and patient factors like age, weight, or other medications. High levels may indicate overdose or poor metabolism, while low levels might mean your dose isn’t working as intended.

Common Side Effects to Watch For

If your levels are too high, you may experience nausea, rapid heartbeat, insomnia, or seizures. If levels are too low, you might feel more breathless or fatigued than usual. Always report any unusual symptoms to your doctor.

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

Why do doctors check theophylline levels regularly?
Doctors monitor theophylline levels to balance its benefits (like improving breathing) with risks (like toxicity). Since theophylline can build up in the body over time and interact with other medications, frequent testing helps prevent dangerous fluctuations.
How often should I get this test?
Your provider will determine the timing based on your medication regimen, health status, and other factors. For example, people with stable conditions may need testing every few weeks, while those with unstable health may need more frequent checks.
Can I drink water before this test?
Yes, you can drink water unless your provider specifies otherwise. Avoid caffeine or alcohol before the test, as they can affect theophylline levels and result accuracy.
  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