Theophylline, Serum

Theophylline, Serum

Number
	007336
CPT
	80198
Synonyms
	Aminophylline, Blood ; Somophyllin® ; Theo-Dur® ; Theolair™ ; Theospan®
Specimen
	Serum or plasma
Volume
	1 mL
Minimum Volume
	0.3 mL
Container
	Red-top tube or green-top (heparin) tube
Collection
	Transfer separated serum or plasma to a plastic transport tube. Do not use a gel-barrier tube. The use of gel-barrier tubes is not recommended due to slow absorption of the drug by the gel. Depending on the specimen volume and storage time, the decrease in drug level due to absorption may be clinically significant. Trough: immediately prior to next dose; after change in dose: children: 2 days, adults: 1-2 days
Storage Instructions
	Refrigerate
Causes for Rejection
	Gel-barrier tube; hemolysis; gross lipemia; icteric specimen
Reference Interval
	Therapeutic: neonatal: 5.0-10.0 μg/mL, adults: 10.0-20.0 μg/mL
Critical Values
	Potentially toxic: neonatal: >10.0 μg/mL, adults: >20.0 μg/mL
Methodology
	Immunoassay
Additional Information
	Theophylline is prescribed for bronchial asthma, for chronic obstructive pulmonary disease, and for newborn apnea. The drug is extensively metabolized¹ with peak serum levels reached 4 hours after oral dose. Troleandomycin and erythromycin may slow theophylline elimination. Heart failure, liver disease, prolonged fever, certain infections, and obesity may have similar effects. Prolonged half-life occurs in premature infants. Dosage should be reduced in these situations. By contrast, half-life is shortened in smokers, variable with phenobarbital administration; higher doses are also tolerated in acidemia. Smokers on the average are reported to need 1.5-2 times as much of the drug as nonsmokers to achieve the same effects. Optimal resampling time after change in dosage is 48 hours for adults, 1-2 days for children. The half-life of theophylline is from 3-10 hours for adults and 1.4-7.9 hours for children, but varies between individuals. Studying serum concentrations and toxic effects, Bertino et al found toxicity with peak theophylline concentrations as low as 19.4 mg/L. Recognizing theophylline toxicity over a wide range of theophylline levels, these authors questioned the association between the severity of toxic effects and serum concentrations.² Aitken and Martin also found lack of correlation between serum theophylline level and toxic effects.³ Blood levels should be interpreted in light of the patient's clinical status and use of other medications. Toxic effects include nausea, vomiting, diarrhea, headache, atrial and ventricular arrhythmias, tremors, and convulsions.
Footnotes
	1. Smith FA. “Theophylline Drug Monitoring of Theophylline, Salicylates, and Acetaminophen,” Clin Lab Med, 1981; 1(3):559-579 (review). 2. Bertino JS Jr, Walker JW. “Reassessment of Theophylline Toxicity: Serum Concentrations, Clinical Course and Treatment,” Arch Intern Med, 1987; 147 (4):757-760. 3. Aitken ML, Martin TR. “Life-Threatening Theophylline Toxicity Is not Predictable by Serum Levels,” Chest, 1987, 91(1):10-14