Immediate Spin Phase

The first of the three classic “phases” of testing serum and red cells for compatibility, most commonly in test tubes (the last two are the 37C and AHG phases). The term “immediate spin” refers to the fact that diluted red cells and patient serum or plasma are added to a test tube at room temperature, immediately centrifuged (“spun”), and then examined visually for agglutination. A positive immediate spin reaction suggests ABO incompatibility between serum and RBCs (and this principle is used in the immediate spin crossmatch) or the presence of a “cold” or room-temperature reactive antibody.

When performing antibody screens or identification using test tubes, a reading at the immediate spin phase is actually not required. However, if it is done, you can identify this phase by the letters “IS” (obviously!), and it will usually be the first reactions listed. See my video on antibody identification basics for more discussion on all the phases of testing. 

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