Adult patient:
Heparin gel tube
Minimum blood volume: 5 mL
Paediatric patient:
Paediatric heparin tube
Number of vials: 1
Minimum blood volume: 1.3 mL
Authorisation code required
No
24 Hr available service
Yes
For suspected theophylline overdose cases, please call Duty Biochemist for 'Urgent' theophylline level testing.
Precaution
General guidelines for sample collection recommend theophylline levels should be measured from 2 - 4 Hr after oral administration (depending on the product formulation) and 30 min after intravenous administration.
Method
Immunoassay
Reference interval
Therapeutic range: 56 - 111 µmol/L
(Source: from manufacturer's kit insert)
Clinical indication
Monitoring theophylline therapy
Result interpretation
During acute illness, the half-life may be prolonged beyond the usual range of 3 - 9 Hr.
Toxicity may develop if the dosage is not reduced. Toxicity may occur within the therapeutic interval in some patients.
In some cases, the most effective therapeutic level may be outside these ranges. Monitor patients for efficacy of treatment for adverse symptoms.
Cigarette smoking reduces the half-life and therefore decreases levels significantly.
The timing of specimen collection can influence the relationship between theophylline concentrations and the clinical response. Other pharmacokinetic factors such as mode of administration, age of patient, concomitant drug therapy, and biological variations in drug absorption should be taken into consideration.
Measurement of uncertainty
Frequency of measurement
Daily