• Also Known As:
  • Aminophylline
  • Formal Name:
  • Theophylline
  • Caffeine
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At a Glance

Why Get Tested?

To determine the concentration of theophylline or caffeine in your blood to establish an appropriate dose and to maintain a therapeutic level; also important to determine if you are experiencing toxicity

When To Get Tested?

At the start of drug therapy and at regular intervals to monitor the drug’s concentration; when indicated, to detect low or excessive (potentially toxic) concentrations

Sample Required?

A blood sample drawn from a vein or from pricking an infant’s heel; the sample is typically collected just prior to the next dose when the drug concentration is expected to be at its lowest level (trough level).

Test Preparation Needed?


What is being tested?

Theophylline and caffeine are drugs that ease breathing and stimulate respiration (methylxanthines). These tests measure the amount of theophylline or caffeine in the blood to help establish an appropriate dose, to maintain a therapeutic level, and to evaluate toxic concentrations.

Theophylline is one of several medications that may be taken by children and adults who have asthma and by adults who have chronic obstructive pulmonary disease (COPD). It is a bronchodilator and functions to relax the muscles in the lungs. Theophylline has a narrow therapeutic window, in which too little theophylline is ineffective and too much can cause toxicity. Both short-acting and long-acting formulations are available for asthma treatments. Acute theophylline toxicity presents with rapid heart rate and nausea. Chronic theophylline toxicity is associated with an increased risk of seizures and abnormal heart rhythms (cardiac dysrhythmias). Both acute and chronic toxicity can be life-threatening.

Caffeine is frequently used for adults as a pain reliever (analgesic), migraine remedies, and to remain alert and/or awake. It is also the preferred medication to treat apnea in premature newborns who stop breathing. Apnea compromises the amount of oxygen available to the body. It is a common and serious condition in premature newborns that must be promptly treated and closely monitored. While both medications can reduce episodes of apnea, caffeine has fewer side effects than theophylline and, thus, a lower risk of toxicity. At very high doses, symptoms similar to those found with theophylline toxicity may be seen.

Establishing and maintaining therapeutic doses can be a challenge. Both theophylline and caffeine levels may need to be monitored because the range of concentrations in which the drugs are effective but not toxic is narrow and in some cases the dose given does not always correlate well with concentrations in the blood.

The rate at which the drugs are processed by the body (metabolized) will vary from person to person. Metabolism is decreased in both the very young and the elderly and increased in smokers. The drug levels may also be affected by underlying conditions such as pneumonialiver disease, hypothyroidism, and by acute infection or illness. Many drugs interact and interfere with the metabolism of theophylline and caffeine. They may increase or decrease its rate of metabolism.

Common Questions

How are the tests used?

Theophylline and caffeine tests are used to monitor the amount of the drugs in the blood to establish appropriate doses, maintain therapeutic levels, and evaluate toxicity.

Theophylline is usually ordered as a trough level – prior to the next dose when the concentration is expected to be at its lowest level. Tests may also be ordered if a healthcare practitioner suspects that a person may be experiencing theophylline toxicity. A series of blood samples may be collected and tested over a period of time to track theophylline concentrations if you have had high theophylline levels, until therapeutic concentrations are reached.

Caffeine blood levels are not used to monitor therapy as routinely as theophylline tests. Usually, newborns receiving caffeine are monitored clinically for episodes of apnea and signs of toxicity, and physiological effects of the drug are closely watched. The majority of those treated respond to standardized doses of the medication without the need for monitoring blood caffeine levels. The test is primarily ordered if an infant is not responding to therapy as expected or if the infant is demonstrating signs of toxicity. Since daily doses and an extended half-life in the premature neonate generally result in stable drug levels, the sample collected is usually a random level, not a trough level.

When are they ordered?

When beginning theophylline treatment, the theophylline test may be ordered several times as the dosage is adjusted as needed, until therapeutic levels are attained. The test may be ordered whenever you have symptoms that your healthcare practitioner suspects are due to theophylline toxicity and whenever you are not responding as expected to therapy. The healthcare practitioner may order a test when you experience a significant change in health status and/or when you start or stop taking a drug that is known to affect the metabolism of theophylline.

Symptoms associated with acute theophylline toxicity may include:

  • Low blood pressure
  • Rapid heart rate
  • Restlessness
  • Tremors
  • Nausea
  • Abdominal pain
  • Confusion
  • Loss of appetite

A caffeine test may be ordered whenever a premature neonate is not responding as expected to treatment and/or whenever an infant has symptoms that the healthcare practitioner suspects are related to high caffeine levels. Signs and symptoms associated with high caffeine levels in a newborn may include:

  • Inability to take in or digest infant formula or breast milk
  • Jitteriness, shakiness
  • Irritability
  • Tremors
  • Rapid heart rate
  • Convulsions

What does the test result mean?

The therapeutic concentration for theophylline, when used as a bronchodilator to treat asthma, is generally considered to be 5–15 mcg/mL (28-83 micromol/L) for adults, 5–10 mcg/mL (28–55 micromol/L) for children and neonates. Levels greater than 20 mcg/mL (111 micromol/L) are considered toxic. Some people may experience significant side effects at concentrations less than 20 mcg/mL (111 micromol/L). When theophylline is used to treat apnea in premature neonates, the therapeutic range is 6-11 mcg/mL (33-61 micromol/L).

Therapeutic concentration for caffeine for the treatment of premature neonate apnea is much wider, 5-20 mcg/mL (25-103 micromol/L), while concentrations greater than 20 mcg/mL (103 micromol/L) are considered toxic, and greater than 50 mcg/mL (257 micromol/L) are considered critical values.

Low levels of theophylline and caffeine may indicate that the drug has not reached a therapeutic level for the individual tested and there is insufficient drug present to be effective.

Blood levels in the therapeutic range mean that most people will have their symptoms relieved without experiencing significant side effects. Adverse side effects and the risk of seizures increase with higher concentrations of these drugs.

Is there anything else I should know?

The use of theophylline as a bronchodilator has decreased as other more effective and less toxic asthma treatments have become available. It is still in use throughout the United States but is not generally the first treatment choice.

In infants, a significant amount of the theophylline dose (8.5%) is metabolized to caffeine. This occurs to a much lesser degree in children and adults. In cases where the theophylline concentration is within the therapeutic range but the infant is showing signs of toxicity, caffeine levels should be determined. Likewise, theophylline is one of the metabolites of caffeine.

Can other drugs I take affect theophylline levels?

Theophylline can affect, and be affected by, a wide variety of drugs and compounds. When your healthcare practitioner prescribes theophylline, it is important for you to list and discuss all of the prescribed and over-the-counter medications that you are taking, including oral contraceptives and any herbal supplements such as echinacea, chamomile, and gingko. Your healthcare provider will also want to know the amount of caffeine and alcohol that you consume and whether or not you smoke.

Should I tell all of my doctors that I am taking theophylline?

Yes; this is an important part of your medical history and will have an effect on other treatment plans.

How long does a premature neonate have to take caffeine?

In most cases, the caffeine is a short-term treatment, given for a few weeks until the baby matures and ceases to have apneic episodes.

You may be able to find your test results on your laboratory’s website or patient portal. However, you are currently at Lab Tests Online. You may have been directed here by your lab’s website in order to provide you with background information about the test(s) you had performed. You will need to return to your lab’s website or portal, or contact your healthcare practitioner in order to obtain your test results.

Lab Tests Online is an award-winning patient education website offering information on laboratory tests. The content on the site, which has been reviewed by laboratory scientists and other medical professionals, provides general explanations of what results might mean for each test listed on the site, such as what a high or low value might suggest to your healthcare practitioner about your health or medical condition.

The reference ranges for your tests can be found on your laboratory report. They are typically found to the right of your results.

If you do not have your lab report, consult your healthcare provider or the laboratory that performed the test(s) to obtain the reference range.

Laboratory test results are not meaningful by themselves. Their meaning comes from comparison to reference ranges. Reference ranges are the values expected for a healthy person. They are sometimes called “normal” values. By comparing your test results with reference values, you and your healthcare provider can see if any of your test results fall outside the range of expected values. Values that are outside expected ranges can provide clues to help identify possible conditions or diseases.

While accuracy of laboratory testing has significantly evolved over the past few decades, some lab-to-lab variability can occur due to differences in testing equipment, chemical reagents, and techniques. This is a reason why so few reference ranges are provided on this site. It is important to know that you must use the range supplied by the laboratory that performed your test to evaluate whether your results are “within normal limits.”

For more information, please read the article Reference Ranges and What They Mean.

View Sources

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2019 review performed by Kamisha L. Johnson-Davis, PhD, DABCC, FAACC, Associate Professor, University of Utah; Medical Director, ARUP Laboratories.

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