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Test Code THEO Theophylline Level, LAB35  


Turbidimetric Inhibition Immunoassay

Performing Laboratory

St. Luke's Hospital Cedar Rapids

Specimen Requirements


Preferred: Green-top (heparin) tube

Acceptable: Gold-top serum gel tube or plain red-top tube

Specimen Volume: 0.1 mL of plasma or serum

Stability: Separate specimens within 2 hours and analyzed immediately or kept at

               2 – 8°C and analyzed within 3 days. For longer storage, samples may be

              frozen at -20 °C for up to 3 months.

Collection Instructions: Peak level should be drawn 2 hours after oral dose of rapid

               release products, or 4 to 8 hours after ingestion of sustained release products.

               Trough level should be drawn immediately prior to next dose.

Note: 1. Theophylline time to steady state is after 2 to 3 days of chronic oral dosing for

               adults and after 1 to 2 days of chronic oral dosing for children.

          2. Levels may be ordered at any time toxicity is suspected.


Reference Values

Therapeutic range: 10-20 mcg/mL

Critical value: >20 mcg/mL

Day(s) Test Set Up

Monday through Sunday

Test Classification and CPT Coding


Useful For

Theophylline levels are useful in the monitoring of therapeutic and toxic levels. Because of the narrow therapeutic index and the wide individual variability in the rate of theophylline metabolism and clearance, patients receiving theophylline should have serum concentrations monitored.