What is your diagnosis?
The light microscopic image demonstrates acute tubular injury with numerous occlusive red blood cell casts, which, despite obtaining deeper levels, is out of proportion to the degree of glomerular injury. While a few glomeruli showed occasional red blood cells within Bowman’s space, there was no evidence of overt glomerular injury or activity such as cellular crescent formation, fibrinoid necrosis, or endocapillary hypercellularity. Thus, while it is a non-specific finding, this degree of red blood cell casts without glomerular proliferation should raise the pathologist’s suspicion for anti-coagulation induced nephropathy. It is essential for the pathologists to probe further into not only if the patient is on anti-coagulation, but whether or not they are supratherapeutic as this typically occurs when the INR is greater than 3. Importantly, while initially described in patient’s taking warfarin, this finding has been seen with many anticoagulants such as dabigatran, rivaroxaban, and others. As a final note, it is important for the pathologist to recognize true red blood cell casts with associated acute tubular injury in these cases before making the diagnosis as biopsies can occasionally show numerous red blood cells within tubular lumens without associated tubular injury along with red blood cells flanking the edges of the biopsy consistent with biopsy artifact.
Reference:
Glassock RJ. Anticoagulant-Related Nephropathy, It’s the Real McCoy. CJASN Jun 2019m 14 (6) 935-937.
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