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Test ID THEO Theophylline

Useful For

Assessing and adjusting dosage for optimal therapeutic level


Assessing toxicity

Method Name

Enzyme-Multiplied Immunoassay Technique (EMIT)

Reporting Name

Theophylline, S

Specimen Type

Serum Red


Specimen Minimum Volume

0.25 mL

Specimen Stability Information

Specimen Type Temperature Time
Serum Red Refrigerated (preferred) 14 days
  Ambient  14 days
  Frozen  14 days

Clinical Information

Theophylline and its congener, aminophylline, are used to relax smooth muscles of the bronchial airways and pulmonary blood vessels to relieve and prevent symptoms of asthma and bronchospasm.


Theophylline is administered orally at a dose of 400 mg/day or 6 mg/kg, whichever is lower, or intravenously as aminophylline at 0.6 mg/kg/hour. Oral dosage may be increased at 200-mg increments to a maximum of 900 mg/day, or 13 mg/kg if the steady-state blood concentration is within the therapeutic range of 10.0 to 20.0 mcg/mL.


Theophylline has a half-life of 4 hours in children and adult smokers, and 7 hours in nonsmoking adults, thus steady-state is reached in approximately 1 day. The volume of distribution is 0.5 L/kg, and the drug is approximately 50% protein bound. Theophylline exhibits zero-order clearance kinetics like phenytoin, small increases in dose yield disproportionately large increases in blood concentration.


Coadministration of cimetidine and erythromycin will significantly inhibit theophylline clearance, requiring dosage reduction. Other drugs such as allopurinol, ciprofloxacin, oral contraceptives, and propranolol inhibit theophylline clearance to a lesser degree.


Smoking induces the synthesis of cytochrome P448, the antipyrine-dependent cytochrome, which significantly increases the rate of metabolism of theophylline. Drugs such as phenobarbital, phenytoin, carbamazepine, and rifampin slightly increase the rate at which the drug is cleared.


Theophylline exhibits rather severe toxicity that is proportional to blood level.

Reference Values


Children and adults: 8.0-20.0 mcg/mL

Neonatal apnea: 6.0-11.0 mcg/mL

Toxic concentration: ≥20.0 mcg/mL


Response to theophylline is directly proportional to serum level.


Patients usually receive the best response when the level is >10.0 mcg/mL, with minimal toxicity experienced as long as the level is <20.0 mcg/mL.


Many drugs affect the plasma level of this drug (as outlined in Clinical Information).

Clinical Reference

1. Pesce AJ, Rashkin M, Kotagal U: Standards of laboratory practice: theophylline and caffeine monitoring. Clin Chem 1998, May;44(5);1124-1128

2. McCudden CR, Broussard LA: Caffeine, lithium and theophylline. In Therapeutic Drug Monitoring Data: A Concise Guide, 3rd edition, Edited by CA Hammett-Stabler, A Dasgupta, AACC Press, 2007

3. Vassallo R, Lipsky JJ: Theophylline: recent advances in the understanding of its mode of action and uses in clinical practice. Mayo Clin Proc 1998;73:346-354

Method Description

This method is performed by enzyme-multiplied immunoassay technique (EMIT) using an Olympus analyzer. The EMIT assay is a homogeneous enzyme immunoassay technique used for the analysis of specific compounds in biological fluids. The assay is based on competition for antibody binding sites between drug in the specimen and drug labeled with the enzyme glucose-6-phosphate dehydrogenase (G6P-DH). Enzyme activity decreases upon binding to the antibody, so the drug concentration in the specimen can be measured in terms of enzyme activity. Active enzyme converts oxidized nicotinamide adenine dinucleotide (NAD) to NADH, resulting in an absorbance change that is measured spectrophotometrically. Endogenous serum G6P-DH does not interfere because the coenzyme functions only with the bacterial enzyme employed in the assay.(Package insert: EMIT Amikacin Assay, Syva Company, Siemens Healthcare Diagnostics, Newark, DE, February 2007)

Day(s) Performed

Test performed daily

Report Available

Same day/1 day

Test Classification

This test has been cleared or approved by the U.S. Food and Drug Administration and is used per manufacturer's instructions. Performance characteristics were verified by Mayo Clinic in a manner consistent with CLIA requirements.

CPT Code Information


LOINC Code Information

Result ID Reporting Name LOINC Code
8661 Theophylline, S 4049-3