Iatrogenic crystalluria

The presence of iatrogenic crystals is a rare event. Except for the Indinavir crystal, a light crystalluria due to a medication or from a contrast agent for X-ray imagery has no clinical significance. On the other hand, an abundant crystalluria associated with a hematuria, a marked cellularity, and oliguria could indicate an obstructive renal disease. The presence of casts with crystalline inclusions clearly indicates that the crystallization is intratubular.

The majority of these drugs crystallize in an acid media often around a pH of 5,0. Drugs of the sulfamides group (sulfamethoxazole, acetylsulfadiazine, sulfadiazine) are the most frequently observed.

A few drugs seen in the urinary sediment

Name	Characteristics	General aspect	Comments
Acetylsulfadiazine, sulfadiazine	Yellow brown crystals of variable shape Asymetric rosette Birefringent		Not to be confused with urates and uric acid. Rarely used today.
Sulfamethoxazole (Septra, Bactrim)	Brown spheres thin plates and rosette		Seen in overdosage
Ampicilline	Fine needles, uncolored		Rare, seen only at very high dose
Contrast agent Renografin Hypaque	Uncolored plates Strongly birefringent Mimics cholesterol		Seen in pale specimen with a density >1,040

Indinavir, a protease inhibitor (antiviral agent) widely used, to treat patients with HIV infection, has been associated with nephrolithiasis. Indinavir is insoluble at physiological pH so that, 20% of the person receiving Indinavir have characteristic crystal in their urine. The crystal are seen as plate-like rectangles exibiting rosette formation

The crystal are birefringent under polarized light with a color dispersion as seen with uric acid. Indinavir crystal, unlike uric acid, are seen at a neutral (6,5 7,5) while uric acid crystals are seen at a more acidic pH (5,0 - 5,5)