Does this test have other names?
Serum theophylline concentrations, blood theophylline level
What is this test?
This test measures the level of theophylline in your blood.
Theophylline is a chemical similar to caffeine. It's sometimes used as a medicine
to treat lung conditions such as asthma, chronic obstructive pulmonary disease, and
bronchiolitis. Sometimes it's prescribed to babies, especially premature infants,
to help their breathing and lung function.
Theophylline reduces inflammation or irritation in lungs and airways, relaxes smooth
muscles in the airways and digestive system, and stimulates the central nervous system.
But theophylline can be harmful in high doses or if the theophylline level in your
blood is too high, so your healthcare provider may want to test your level of theophylline.
Why do I need this test?
You may need this test if your healthcare provider gives you theophylline for a health
condition. The test will help your provider determine the proper dose and see if you
have too much theophylline in your body. Too much theophylline can be life-threatening.
Signs and symptoms of too much theophylline include:
Vomiting, heartburn, and belly pain
Rapid heart rate or other changes in heart rhythm
Muscle aches and tremors
High blood sugar
Low blood pressure
What other tests might I have along with this test?
Your healthcare provider may order other tests if you have taken too much theophylline.
Tests to measure other substances in your blood, such as blood sugar and electrolytes
Blood gas test to check the oxygen and carbon dioxide levels in your blood
Liver function tests
What do my test results mean?
Test results may vary depending on your age, gender, health history, the method used
for the test, and other things. Your test results may not mean you have a problem.
Ask your healthcare provider what your test results mean for you.
Results are given in micrograms per milliliter (mcg/mL). Safe levels for people taking
theophylline are usually 10 to 20 mcg/mL. Levels above 20 mcg/mL may be harmful and
can happen if people take too many pills within a short time period. Such cases might
include accidentally taking extra pills or having a prescription that was written
for too high a dose. This may also happen if someone was using the medicine to attempt
A safe level for you depends on how much alcohol you drink, whether you smoke, whether
you take herbal medicines, and how nutritiously you eat.
How is this test done?
The test is done with a blood sample. A needle is used to draw blood from a vein in
your arm or hand.
Does this test pose any risks?
Having a blood test with a needle carries some risks. These include bleeding, infection,
bruising, and feeling lightheaded. When the needle pricks your arm or hand, you may
feel a slight sting or pain. Afterward, the site may be sore.
What might affect my test results?
Certain medicines cause theophylline to break down more slowly in the body, which
can lead to higher test results. These include:
Cimetidine, used to treat problems related to stomach acid
Birth control pills
Certain antibiotics, such as erythromycin, clarithromycin, ciprofloxacin, and norfloxacin
Fluvoxamine, a medicine for anxiety
Other medicines cause theophylline to leave your body more quickly. This leads to
a lower test result. Smoking, drinking alcohol, or having a viral infection or heart
failure can cause levels to suddenly go up or down.
How do I get ready for this test?
Tell your healthcare provider how much theophylline you have taken. Be sure your healthcare
provider knows about all medicines, herbs, vitamins, and supplements you are taking.
This includes medicines that don't need a prescription and any illicit drugs you may