Use of plasma instead of serum in laboratory tests for infectious mononucleosis.

Until recently, the exclusive use of serum in all laboratory tests for detecting heterophile antibody has remained unquestioned. This communication describes a series of studies which demonstrate that comparable results are obtained when sequestrenized plasma is used instead of serum in the conventional differential absorption technique and in two slide screening tests. It is confirmed that significant differences in the final differential absorption titres can result from variations in the agglutinability of erythrocytes from different sheep but such differences when present are the same for plasma as for serum. The advantages of using plasma for routine purposes are briefly discussed.