The Test Sample
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 and to maintain a therapeutic level.
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 with a narrow therapeutic window – too little theophylline is ineffective, 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. 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 metabolized will vary from person to person; it 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 pneumonia, liver 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.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm. In infants, blood may be collected by pricking a heel.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.