Interference with alpha-antitrypsin studues in stored serum by presumed bacterial proteases.

Contamination of werum by certain gram-negative bacteria has been shown to spoil the serum for measurement of trypsin inhibitory capacity (STIC) or for antitrypsin phenotyping. Such sera develop intense fibrinolytic activity when the STIC has dropped to itsminimal level, but antitrypsin concentration as measured by radial immunodiffusion remainsconstant. Cultures of ENTEROBACTER, Klebsiella, Bacillus subtilis, and Pseudomonas species were shown to have this capability, but production of the fibrinolytic enzyme by the bacteria was most proficient in the presence of human serum. The enzyme is believed to be of bacterial origin because of its lack of esterase activity, and because activation of serum plasmin by streptokinase did not affect the STIC. Care mustbe taken to avoid bacterial contamination of blood that is to be submitted for an STICassay and/or antitrypsin phenotyping. Serum should be prepared quickly, frozen soon,and stored and transported in a frozen state.