Cystine crystalluria

Cystine crystals are colourless and have a characteristic hexagonal form (benzene ring) with either equal or unequal length of sides (Fig. 25-26).

They may occur single but mostly agglomerate in layers. They are easier to detect at reduced light intensity for they’re thin. Cystine crystals are mostly forming themselves in concentrated acid urine. If strongly alkaline urine as a result of infection or contamination is produced by urase forming bacteria, it may lead to a dissolving of cystine crystals. The admixture of acetic acid with cooling and centrifugation afterwards may increase the detection rate of typical crystals in alkaline urine. Cystine crystals are insoluble in acetic acid, alcohol, acetone, ether and boiling water. They dissolve in ammonia and hydrochloric acid.

Interpretation
Cystine crystalluria is not a meaningless result. Stones of cystine may develop in dogs and cats which have the metabolism disorder cystinuria though not every patient with cystinuria develops bladder calculus of cystine (see also discussion of magnesium phosphate- and uric acid-crystalluria related to differentiation of cystine crystals from struvite or uric acid crystals).

Some of the medicaments that have been segregated in the urine may develop crystals. Maybe the most famous crystalluria in dogs and cats related to medicaments is the one by ingesting sulfonamide. Sulfonamides may precipitate in urine as characteristic bundles of transparent or brownish needles, usually eccentric bundled (Fig. 27-29). They may also appear as amorphous crystals or spheres with radial striation (Fig. 30). A positive lignin test confirms the sulfonamide crystalluria diagnose.

Leucine crystals in humans indicate a serious liver disease. The relevancy of leucine crystals in dogs is not extensively researched until now (see also: cystinuria in the Newfoundland dog)

Fig.25)
Microphotographic picture from cystine crystals in the urine sediment from a two-year-old male bulldog with bladder calculus of cystine.

Fig.26)
Scanning electron microscope picture from cystine crystals in the urine sediment from the dog from fig. 25.

Fig.27)
Microphotographic picture from sulfadiazine crystals in the urine sediment from a two-year-old castrated male Siamese cat who got Trimethoprim-Sulfadiazine per os.

Abb. 28)
Mikrophotographische Aufnahme eines fächerförmigen Sulfadiazinkristalls im Harn der Katze von Abb. 27.

Fig. 29)

Scanning electron microscope picture from the surface of a bladder calculus of calcium oxalate which has been removed from a ten-year-old castrated male Malteser. Look at the fan shaped sulfadiazine crystal.

Fig. 30)
Scanning electron microscope picture from a sulfadiazine crystal in the urine from the cat from fig. 27.