Urinary trypsin inhibitory activity for the diagnosis of bacterial infection: a prospective study in 690 patients

During the acute phase response, interleukin-1 induces production of inter-alpha-trypsin inhibitor. The measurement of urinary trypsin inhibitory activity which results from the effects of inter-alpha-trypsin inhibitor degradation products is easy, quick and inexpensive. We conducted a prospective study to investigate its value as a diagnostic tool in comparison with C-reactive protein.

Comparisons were made in 690 consecutive patients at admission to a department of internal medicine.

The level of urinary trypsin inhibitory activity was significantly higher in patients with bacterial infection (mean = 123 IU/g creatinine) than in patients with either viral infection (34 IU), cancer (50 IU), elevated erythrocyte sedimentation rate without infection (45 IU), miscellaneous non-inflammatory diseases (27 IU) or in non-organic controls (19 IU) (Dunnet's test, p << 0.01). The receiver operating characteristic curve showed that sensitivity and specificity of urinary trypsin inhibitory activity were higher than those of C-Reactive protein for the diagnosis of bacterial infection. For levels > or = 60 IU, sensitivity was 75% and specificity 89%. Urinary trypsin inhibitory activity levels fell within 2 days in patients treated for acute bacterial infection.

Urinary trypsin inhibitory activity could be a useful marker of bacterial infection particularly in patients with fever of unknown origin and/or elevated erythrocyte sedimentation rate.