A screen will be performed on all specimens first to identify most of those with titer values in the normal range. If the screen is negative, no titration will be performed and the screen will be reported as negative. If the screen is positive, a titer will be performed and the screen will be reported as positive.
The titer is determined by making serial doubling dilutions of the patient's serum in 0.9% saline. Group O indicator red cells are added and the serum-cell mixture is then incubated 20 minutes at 0 to 5 degrees C, and the titer end point range is determined.(Ellenhorn MJ, Weiner D: Variables in determination of cold hemagglutinins. Am J Clin Pathol 1953;23:1031-1039)