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Theophylline Concentration in 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 stays within safe levels.

Quick summary

["This test helps doctors check if your theophylline medication is working properly and avoid dangerous levels."]

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

Key facts at a glance

LOINC
13582-2
Short code
Theophylline Fld-mCnc
Synonyms
Theophylline Fld-mCnc
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 doctor may order this test if you’re taking theophylline (such as Theo-Dur or Theobid) to treat conditions like asthma, chronic obstructive pulmonary disease (COPD), or heart rhythm issues. Regular monitoring helps prevent side effects like rapid heartbeat or nausea.

What to Expect Before the Test

No special preparation is needed. You’ll provide a blood sample, usually drawn from your arm in a clinic or lab. The test is quick and painless.

What the Results Mean

Results help your doctor adjust your dose if needed. Low levels may mean your medication isn’t working well, while high levels could indicate toxicity. Your doctor will discuss these findings with you.

Common Uses and Conditions

This test is primarily used in patients on long-term theophylline therapy to maintain therapeutic levels and avoid overdose risks.

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 might my doctor want to check my theophylline level frequently?
If you have conditions like asthma, COPD, or heart rhythm disorders, your doctor may check your levels more often, especially if you’re taking other medications that interact with theophylline (like caffeine, fluoroquinolones, or macrolide antibiotics). This helps prevent dangerous buildup.
How often should I get this test?
Your doctor will determine the timing based on your medication schedule, health status, and other factors. Follow their instructions—some patients need testing every few days or weeks.
What happens if my theophylline level is too high?
If levels are dangerously elevated, your doctor may reduce your dose, switch to a different medication, or monitor you closely for symptoms like headache, nausea, rapid heart rate, or seizures. Immediate medical attention may be needed in severe cases.
  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