a test for nonagglutinating Rh antibodies: an Rh agglutination test is first carried out; if the test result for Rh agglutinins is negative, then 1 drop of anti-Rho agglutinating serum of moderate titer is mixed with the patient's serum containing Rh-positive test cells; if after incubating for from 1-2 hours at 37°C no agglutination occurs, Rho-blocking antibodies are assumed to be present in the patient's serum.