The most likely diagnosis is atheroembolism of cholesterol crystals. Disruption of an atheromatous plaque by instrumentation or anticoagulation during this patient's cardiac catheterization likely caused embolization of cholesterol crystals from the plaque through the arterial circulation distal to the point of disruption. These crystals lodge in capillary beds and cause vascular obstruction but also trigger an inflammatory response. Acute kidney injury (AKI) is a common result of cholesterol embolization, which causes peripheral eosinophilia and hypocomplementemia and shows evidence of inflammation on urinalysis, frequently with eosinophiluria present. Embolization may also lead to digital ischemia or infarction (“blue toe” syndrome) due to digital arterial occlusion or central scotoma due to central retinal artery occlusion. Although not specific for cholesterol atheroembolism, livedo reticularis (areas of lace-like mottled and purplish skin over the legs and thighs) is commonly associated with this disorder. Management is primarily supportive; anti-inflammatory agents (such as glucocorticoids) are not routinely given for treatment of cholesterol atheroembolism.

Acute interstitial nephritis (AIN) should be suspected following the initiation of new medications, although none of the agents this patient is taking has been reported as a cause of AIN. A diffuse rash, but not livedo reticularis, is characteristic of AIN. Eosinophiluria was previously believed to diagnose AIN, but urine eosinophil determination has been shown to be neither sensitive nor specific in the diagnostic evaluation of AIN.

Contrast-induced nephropathy (CIN) is a diagnostic consideration given the dye load associated with cardiac catheterization. However, CIN typically presents as acute tubular necrosis with granular casts, and AKI due to CIN typically peaks at 24 to 72 hours but improves within 5 to 7 days.

Polyarteritis nodosa (PAN) is a necrotizing vasculitis of medium-sized arteries, sometimes associated with hairy cell leukemia or infection with hepatitis B or C. PAN may present with livedo reticularis, as in this patient, but kidney manifestations usually include renal arterial aneurysms with perirenal hematomas and severe hypertension, which findings are missing here. This patient also lacks any of the other neurologic or gastrointestinal manifestations of PAN.