Calcium phosphate crystalluria

There are several different types of calcium phosphate crystals. They seem to be differently described as amorphous phosphate and calcium phosphate. Excepting brushite the calcium phosphate crystals tend to form themselves in alkaline urine.  Amorphous phosphates which are being observed through an optical microscope resembles to amorphous urates (fig. 18-21). Though amorphous phosphates are typically forming themselves in alkaline urine and are dissolving themselves in acetic acid. Urates on the other hand often have yellow grainy appearance and aren’t dissolving in acetic acid but in lyes at a temperature of 60°C.

Scanning electron microscope pictures from amorphous phosphates which have been found in human urine reveal that they usually appear spherical but may also take the form of a ring or mold. Only in dogs have we observed the spherical habit of calcium phosphate. Calcium phosphate may also form long thin colourless prisms sometimes with pointed ends. These crystals can agglomerate to rosettes or appear as needles. Calcium phosphate also may precipitate in acid urine as an elongated brushite crystal (fig. 22-23). It was considered that if calcium phosphate should precipitate from an aqueous high oversaturated solution with a pH value >7, amorphous crystals are appearing in the beginning. The amorphous precipitate is able to transform itself into a stable crystalline precipitate by dissolving, conversion and crystal growth. The pace of this transformation depends form the pH value because the stability of amorphous phosphates gets stronger in an environment with a high pH value.

Interpretation
The interpretation of amorphous crystals which are found with the optical microscope has to be made with care because they form themselves from a multitude of crystals including calcium phosphate, ammonium urate and xanthine. According to our own experiences a great amount of crystals consisting of probably calcium phosphate was observed in clinical unsuspicious dogs, dogs with constant alkaline urine, dogs with calcium phosphate urinary calculus and dogs with urinary calculus which had been a mixture from calcium phosphate and calcium oxalate. Small amounts of calcium phosphate crystals may occur in connection to infection related crystalluria.

Fig. 18)
Microphotographic picture from amorphous calcium phosphate and magnesium ammonium phosphate crystals in urine from a two-year-old castrated short hair male cat.

Fig. 19)

Microphotographic picture from amorphous calcium phosphate crystals in urine from a three-year-old male Lhasa-Apso. The dog had bladder calculus of calcium oxalates.

Fig. 20)

Scanning electron microscope picture from a calcium oxalate dihydrate crystal and several amorphous calcium phosphate crystals in the urine from the dog from frig. 19.

Fig. 21)

Scanning electron microscope picture from amorphous calcium phosphate crystals in the urine sediment from a five-year-old castrated male Shi-Tzu.

Fig. 22)

Microphotographic picture from calcium hydrogen – phosphate dihydrate – (brushite-) crystals in the urine sediment from a three-year-old male Dwarf Schnauzer with bladder calculus of calcium oxalates.

Fig. 23)
Microphotographic picture from a big calcium hydrogen phosphate dihydrate – (brushite-) crystal and characteristic calcium oxalate dihydrate crystal in the urine sediment from a horse.