A compatibility test between donor red blood cells and recipient serum or plasma, performed in a test tube or other testing platform. There are two main types of serologic crossmatch: 1) Immediate-spin crossmatches, and 2) AHG crossmatches. The serologic crossmatch is by far the most commonly used compatibility test between donors and recipients, and it is essentially always a major crossmatch. The computer crossmatch is not a serologic crossmatch (though it is an acceptable alternative to an immediate spin crossmatch), as no actual contact between donor and recipient samples occurs.