Kidney biopsy showing histologic findings of anticoagulant-associated nephropathy

RBCs in different compartments of the kidney in patients on warfarin therapy with acute kidney injury.
(A) Numerous RBCs and RBC occlusive casts were noticed in tubules and Bowman space (Hematoxylin and eosin stain; original magnification x200).
(B) Immunohistochemical stain for Tamm-Horsfall protein shows that most RBC casts do not contain Tamm-Horsfall protein. Positively stained thick ascending loop of Henle (arrow).
(C) Immunohistochemical stain for cytokeratin AE1/AE3 (arrows, dark brown) highlights distal tubules with occlusive RBC casts (counterstain with hematoxylin/eosin; original magnification x200).
(D) Dysmorphic RBCs were noticed in several tubules by means of electron microscopy (uranyl acetate, lead citrate stain; original magnification x3000).