Direct Coombs' is used to detect antibodies already bound to red cells, while in the indirect test, one adds the serum in question to known Rh+ red cells.
	Explanation. In the direct test, anti-human Ig antibodies are added directly to the red cells in question to determine if there are antibodies already bound to them.

Immunological Techniques
University of Arizona
douglas.lake@asu.edu

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