Clinical Lab Handbook

Container/Tube: SST

Alternate Container: Red top

Specimen Volume: 5 mL

Collection Instructions: Allow specimen to clot for 30 minutes. Spin specimen in centrifuge.

Rate, Enzymatic

A drop of patient sample is deposited on the slide and is evenly distributed by the spreading layer to the underlying layers. p-Nitrophenyl phosphate (PNPP) migrates from the spreading layer to the reagent layer. If no theophylline is present, the alkaline phosphatase reaction proceeds at its maximum rate. If theophylline is present, it uncompetitively inhibits the beef liver isoenzyme, and the reaction rate is reduced. The assay is performed at pH 8.2 so that samples containing endogenous alkaline phosphatase (maximum activity at pH 10.5) will not interfere. The product, p-nitrophenol, remains in the transparent reagent layer.

Following addition of the sample, the slide is incubated and the reflection density measured after 1.17 and 2.5 minutes. The difference in reflection density between the two readings is proportional to the theophylline concentration in the sample.

Theophylline is a drug used in the treatment of asthma. Theophylline is an effective bronchodilator. The therapeutic and toxic effects of theophylline are related to the plasma concentrations of the drug. Theophylline measurements are used to monitor patient compliance and therapy and to diagnose potential overdose. Toxic effects include nausea, vomiting, diarrhea, headache, tachycardia, arrhythmias, and convulsions.

Therapeutic concentration: 10-20 µg/mL

Critical value (automatic call-back): >20 µg/mL

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