The influence of ionic strength and incubation time on the sensitivity of methods using papainized red cells.

The sensitivity of a combination of various papain methods with normal and low ionic strength (lis) of the serum-cell mixture for the detection of red cell antibodies was tested after varying periods of incubation of the mixture. The mixture was centrifuged before reading when the period of incubation was short. The maximum sensitivity without centrifugation was always reached after a period of 60 min. With a longer incubation the sensitivity decreased. A sensitivity that equalled the maximum sensitivity without centrifugation could be obtained after only 10 min of incubation, if it was followed by a centrifugation before reading. Lis consistently increased the sensitivity of the papain methods, especially after 45--60 min of incubation.