Comparison of serum theophylline concentrations measured by high pressure liquid chromatography and quantitative enzyme-multiplied immunoassay technique.

Safe, effective theophylline therapy depends on the rapid determination of serum theophylline concentrations. Two rapid methods that require less than 0.1 ml of serum are high pressure liquid chromatography (HPLC) and quantitative enzyme-multiplied immunoassay technique (EMIT). A comparison of these two methods was carried out using 117 serum samples routinely collected from asthmatic patients in Charity Hospital of Louisiana at New Orleans. After determination by the EMIT method, specimens were analyzed by HPLC in a different laboratory. Mean serum theophylline concentrations in 100 specimens containing more than trace concentrations were 14.5 mcg/ml by the EMIT method, compared with 12.1 mcg/ml by HPLC. The paired t test showed this to be a highly significant difference (p less than 0.0005). Whichever method of determination of theophylline concentration is used, frequent validation of results by comparison with those of other laboratories seems indicated.