Theophylline interference with the phosphotungstate uric acid test

The effect of theophylline on serum uric acid measurements was studied. Serum uric acid levels were measured by the phosphotungstate method in eight healthy adults, three of whom received a single u.3-mg/kg oral theophylline dose (as aminophylline elixir) while fasting, and in 15 fasting nonuremic patients (age 14 to 51 years) on chronic oral aminophylline therapy. Uric acid levels also were measured in vitro for serum with known amounts of theophylline (0-49 microgram/ml). Serum theophylline levels were measured by high-pressure liquid chromatography for the patients receiving chronic theophylline therapy and spectrophotometrically for the subjects receiving a single oral dose. In the 15 chronic theophylline patients, actual total serum uric acid levels were not significantly different (p greater than 0.05) from those expected had they been a normal population (i.e., healthy, not receiving theophylline). Likewise, in vitro studies showed no difference in uric acid levels of serum exposed to various concentrations of theophylline. A positive correlation (r greater than or equal to 0.816) between serum theophylline and uric acid levels was found in two of the three single-dose studies, suggesting a pharmacological interaction. Therapeutic serum theophylline levels do not interfere with the measurement of serum uric acid levels by the phosphotungstate method.