A cellulose acetate membrane precipitin (CAP) test for amoebiasis.

A simple precipitin test (CAP) using cellulose acetate membrane has been devised and evaluated against the gel diffusion precipitin (GDP) test. In 251 sera tested by both methods, the CAP was never negative when the GDP was positive (110 sera). 34 sera were negative by the GDP but positive by the CAP; in all of these the patients either had a past history of amoebiasis or were considered to have active amoebiasis. The CAP is technically very simple, the result is available within four and a half hours, and the membranes can be impregnated with antigen and stored for several months. The CAP is slightly more sensitive than the GDP and remains positive longer after the patient has been cured; it seems to be equally specific.