Theophylline

Blood

Report in 12Hrs

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No Fasting Required

Details

Drug level monitoring.

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Theophylline Test Information Guide

Why is it done?
- Measures serum or plasma theophylline levels to ensure therapeutic drug concentrations in patients receiving theophylline for respiratory conditions
- Monitors therapeutic efficacy in asthma, chronic obstructive pulmonary disease (COPD), and other obstructive airway diseases
- Detects toxic or subtherapeutic drug levels that may require dose adjustments
- Performed when initiating theophylline therapy, following dose adjustments, or when symptoms suggest toxicity or inadequate control
- Used to evaluate drug interactions or compliance issues in patients on chronic theophylline therapy
- Typically drawn 4-6 hours after dosing (peak level) or just before the next dose (trough level)
Normal Range
- Therapeutic Range: 10-20 mcg/mL (55-110 micromoles/L)
- Units of Measurement: micrograms per milliliter (mcg/mL) or micromoles per liter (micromoles/L)
- Low (Subtherapeutic): Less than 10 mcg/mL - inadequate drug level for therapeutic effect; may result in poor symptom control
- High (Toxic): Greater than 20 mcg/mL - elevated risk of adverse effects and toxicity
- Critical/Severe Toxicity: Greater than 30 mcg/mL - life-threatening levels requiring immediate intervention
Interpretation
- Therapeutic Range (10-20 mcg/mL): Optimal level for bronchodilation and symptom relief with minimal adverse effects; continue current dose
- Below Therapeutic (Less than 10 mcg/mL): Indicates insufficient drug level; may require dose increase or more frequent dosing; assess compliance and drug absorption
- Mild Toxicity (20-25 mcg/mL): Early signs of toxicity may appear; symptoms include nausea, vomiting, headache, insomnia; requires dose reduction
- Moderate Toxicity (25-30 mcg/mL): Significant toxicity with tachycardia, arrhythmias, tremor, and gastrointestinal symptoms; dose should be reduced or discontinued
- Severe Toxicity (Greater than 30 mcg/mL): Life-threatening toxicity; risk of seizures, severe cardiac arrhythmias, hypotension, altered mental status; requires emergency intervention and possible dialysis
- Factors Affecting Results: Liver disease, congestive heart failure, elderly patients, smoking status, diet, caffeine intake, drug interactions (cimetidine, macrolide antibiotics, fluoroquinolones), fever, and pregnancy can all affect theophylline metabolism and levels
- Timing of Sampling: Peak levels (4-6 hours after dose) reflect drug absorption and distribution; trough levels (just before next dose) reflect drug elimination; consistent timing ensures accurate interpretation
Associated Organs
- Primary Organ Systems: Respiratory system (lungs, bronchi), central nervous system, cardiovascular system, and hepatic system (liver where theophylline is metabolized)
- Conditions Associated with Abnormal Results: Asthma, COPD, emphysema, chronic bronchitis, apnea (particularly in premature infants)
- Liver Disease Impact: Hepatic dysfunction impairs theophylline metabolism, leading to elevated levels; cirrhosis, hepatitis, and fatty liver disease increase toxicity risk
- Cardiovascular Complications: Theophylline toxicity can cause tachycardia, cardiac arrhythmias (atrial fibrillation, ventricular tachycardia), hypotension, and myocardial infarction; chronic congestive heart failure reduces drug clearance
- Central Nervous System Effects: Toxicity manifests as seizures, tremor, agitation, anxiety, insomnia, headache, and altered mental status; severe toxicity can precipitate status epilepticus
- Gastrointestinal Effects: Nausea, vomiting, diarrhea, abdominal cramps, and gastrointestinal hemorrhage may occur with elevated levels
Follow-up Tests
- Repeat Theophylline Levels: Performed 4-6 hours after dose adjustment to confirm therapeutic range; typically rechecked 3-5 days after dose changes
- Liver Function Tests (LFTs): Assess hepatic function and metabolism capacity; ALT, AST, bilirubin, and albumin help determine if liver disease affects theophylline clearance
- Electrocardiogram (ECG): Indicated when levels are elevated or toxicity symptoms present; detects cardiac arrhythmias and ischemia
- Blood Glucose Monitoring: Theophylline may affect glucose metabolism; baseline and periodic monitoring recommended in diabetic patients
- Pulmonary Function Tests (PFTs): Assess therapeutic effectiveness by measuring forced expiratory volume (FEV1) and other respiratory parameters
- Renal Function Tests: Baseline creatinine and BUN assessment; renal disease may require dose adjustment
- Monitoring Frequency: Initial level 3-5 days after therapy starts or after dose changes; then every 6-12 months during maintenance therapy; more frequently if symptoms suggest toxicity or compliance issues
Fasting Required?
- Fasting Required: No
- Food and Beverage: Fasting is not required for the blood draw; patient may eat and drink normally before the test
- Caffeine Intake: Although caffeine is not restricted, it is recommended to note caffeine consumption in diet (coffee, tea, chocolate, cola) as it may slightly affect results; avoid excessive caffeine 24 hours before test if possible
- Medications: Continue all medications including theophylline as prescribed; do not skip doses before the test; inform healthcare provider of all medications, supplements, and herbal products being taken
- Timing of Sample Collection: This is the most critical factor; blood should be drawn at the same time relative to dose each time (typically 4-6 hours after dose for peak level or just before next dose for trough level); consistent timing must be communicated to the laboratory
- Special Instructions: Inform phlebotomist of the exact time of last theophylline dose; wear comfortable clothing with easily accessible veins; inform staff of any recent illness, fever, or significant dietary changes

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