Theophylline Concentration (Serum/Plasma)
This test measures the amount of theophylline, a medication used to treat certain breathing and heart conditions, in your blood.
["Helps ensure your medication dose is safe and effective."]
Key facts at a glance
- LOINC
- 32116-6
- Short code
- Theophylline Trough SerPl-sCnc
- Synonyms
- Theophylline Trough 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 Is This Test Done?
Your healthcare provider may order this test if you’re taking theophylline (a medication like Theophylline, Theo-Dur, or Slo-Bid) to manage conditions like asthma, chronic obstructive pulmonary disease (COPD), or certain heart rhythms. It helps monitor your drug levels to avoid side effects like rapid heart rate or nausea while ensuring the medication works properly.
What to Expect Before the Test
No special preparation is needed. You may have a small needle inserted into a vein (usually in your arm) to draw a blood sample. The process is quick and usually painless. If you’re on a blood thinner, let your provider know before the test.
What the Test Results Mean
Results show your current theophylline concentration in your blood. While reference ranges vary by lab and patient factors, your provider will compare your result to your usual therapeutic range to guide dosing adjustments. High levels may indicate too much medication, while low levels may mean you need more.
Possible Side Effects and Risks
Theophylline can cause side effects like nausea, headache, or an increased heart rate. Very high levels may lead to serious issues like seizures or irregular heartbeat. Your provider will adjust your dose based on these results to keep you safe.
Reference range
Therapeutic: 10-20 mcg/mLN/A
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.
Maintaining proper theophylline levels is critical because this medication can be toxic at high concentrations. Regular monitoring helps prevent complications, especially in patients with liver or kidney issues, who may metabolize the drug differently. It also ensures the medication remains effective against your condition.
Short name
Theophylline Level
Frequently asked questions
What does a ‘trough’ level mean?
Why is this test done at a specific time?
Can I eat or drink before this test?
Sources
- 1
- 2Lab Tests OnlineSource
- 3
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.
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