Q: What is the gold standard test to confirm cholesterol emboli?

Answer: Tissue biopsy

No laboratory testing is specific for cholesterol emboli. Diagnosis can be definitive via debrided tissue or thrombectomy specimen. The histologic hallmark of cholesterol crystal embolism is the presence of "ghosts" of cholesterol crystals or cholesterol clefts within arterioles. This is due to the fact that the convex-shaped crystals within the small arterioles of the kidney dissolve during the fixation process leaving the ghosts.

Reference:

Warren BA, Vales O. The ultrastructure of the stages of atheroembolic occlusion of renal arteries. Br J Exp Pathol 1973; 54:469.