Antidotes alone do not influence blood clot morphology. Blood clots were generated by incubating antidotes in noncitrated whole blood at 37°C. (A-B) Blood clots formed in the presence of both andexanet alfa and PER977 did not show any major morphological changes. Clot images were taken at 2 magnifications (original magnification ×2500 and ×5000, respectively. Only images from the ×5000 magnification are depicted (scale bars, 5 µm). (C-D) Blood clot fiber diameters formed in the presence of andexanet alfa or PER977. Fiber diameter was measured from scanning electron micrographs using ImageJ software. A total of 60 fibers were analyzed from 2 independent experiments. Fibers for size analysis were selected from 4 images by probing 4 different spots in each image. Data are median with interquartile ranges (n = 60). Black horizontal lines represent median, and error bars represent interquartile range. Statistical significance for fiber diameter was determined by comparing the antidote-treated group to the buffer control using a Kruskal-Wallis test followed by a Dunn post-test. Asterisks indicate significant differences in comparison with the buffer control. Fibers formed in the presence of 500 µg/mL andexanet alfa are significantly thinner than those in the control clot (**P < .005). ns, not significant.