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Laboratory Medicine

Test Directory / Theophylline


Brown clotted serum, gel barrier or lithium heparin

Common AbbreviationsTHE
Tube typeBrown clotted serum, gel barrier or lithium heparin
Clinical IndicationTheophylline is a methylxanthine derivative widely used in the treatment of asthma, obstructive lung disease and neonatal apnea. The effect of theophylline is closely correlated with the concentration of drug in the serum. Measurement is performed to check therapeutic levels and compliance. Toxic effects usually occur at concentrations >20mg/L in adults. These effects include anorexia, nausea, vomiting, headaches and nervousness. Severe side effects such as cardiac arrest can occur at concentrations >40mg/L. Theophylline has slow elimination in obese patients, patients with hepatic disease and in those on a high carbohydrate, low protein diet. Premature infants have very low rates of theophylline elimination. Monitoring serum theophylline levels provides useful information in adjusting dosage to achieve optimal levels while avoiding drug toxicity.
Specimen TypeBlood
Sample typeSerum or plasma
Minimum Volume0.5mL If requesting more than 10 tests please send an additional brown clotted serum sample.
Special PrecautionsNo special requirements
Stability3 months at 2–25°C
Turnaround TimeUrgent: 2 hours Inpatient: 6 hours Outpatient/ GP: 24 hours
LaboratoryYork and Scarborough
Reference IntervalTherapeutic range: 10 - 20 mg/L (Adults) This range is based upon a sample taken at 4-6 hours post last dose and is also dependent upon the drug preparation used.
LimitationsSamples containing antibodies to E. coli ?-galactosidase may result in artificially high results which will not fit the clinical profile. The incidence of patients having such antibodies is extremely low. Due to cross-reactivity with 1,3-Dimethyluric Acid, the theophylline assay should not be used to quantitate samples from uremic patients. As with any assay employing mouse antibodies, the possibility exists for interference by human anti-mouse antibodies (HAMA) in the sample, which could cause falsely elevated results.
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