FXIIIa does not require α₂-antiplasmin, TAFI, or fibronectin to promote RBC retention in clots. Serum RBC content from ex vivo clot contraction assays using whole blood from (A) WT, α₂-antiplasmin–deficient (α₂-AP^−/−), and TAFI-deficient (TAFI^−/−) mice (n = 3) or (B) fibronectin-sufficient (pFn⁺) and -deficient (pFn⁻) mice (n = 6-9). Clotting was initiated with TF (1 pM, final) and recalcification (10 mM, final). WT and pFn⁺ blood was treated with T101 (5 μM, final) as positive controls. Bars are means ± SE.