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ATLAS OF URINE SEDIMENT - Crystals

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ATLAS OF URINE SEDIMENT - Crystals

ATLAS - Crystals

CD Chapter Outline:

Crystals are frequently found in the urine, however, usually they are not present in fresh urine. The presence of crystals in fresh urine is considered to be an artifact. Crystals are formed by concentration and saturation of the urine chemical constituents, or by their reduced solubility, which is observed if the urine is stored at a temperature lower than body temperature.
On urinary sediment examination, it is important to identify the type of crystals, i.e. whether they are normal, diagnostically irrelevant crystals, or crystals indicative of a disease. The following crystals without clinical significance are mostly found in the urine:

 at acidic pH: uric acid, amorphous urates, calcium oxalates
 
at alkaline pH: amorphous phosphate, triple phosphate, calcium oxalate,
  alcium carbonate, ammonium urate
 
crystals found in urinary sediment due to pathologic processes: cystine, tyrosine, and leucine.

 
 Calcium oxalate crystals
Two forms of calcium oxalate crystals can be found in urinary sediment. Calcium oxalate dihydrate is more commonly present. The mineralogical term for calcium oxalate 2(H2O) is weddelites. The other form of calcium oxalate is a monohydrate, its mineralogical term being whewellites. The two forms of calcium oxalate have different crystallographic characteristics. Calcium oxalate crystals mainly occur in acidic urine, however, they may also be found in slightly alkaline urine.
 Uric acid crystals
Uric acid crystals are of a varying size and shape. They may be rhomboids, quadrangles, hexahedral prisms, or shaped like a spindle, rosette, barrel, or rarely like a needle or spear. They are yellowish to yellow-brown in color. Uric acid crystals usually are of a characteristic yellow color.
Color intensity depends on crystal thickness, so that thin plates are colorless, while massive crystals are brownish. Uric acid crystals are clinically relevant only if found in fresh urine. These crystals are found in a highly concentrated urine, in elevated body temperature, gout, diseases characterized by increased degradation of cellular nuclei, e.g., leukoses, or in patients receiving cytostatic therapy for malignant diseases, and occasionally in renal tubular diseases. Uric acid crystals may occur due to metabolic or pathologic events.
 Triple phosphate (ammoniomagnesium phosphate - struvite)
Urinary concentration of ammonium is the major factor in the formation of triple phosphate crystals. Alkalization of a urine specimen with ammonium leads to the formation of triple phosphate, as differentiated from alkalization of urine with sodium hydroxide where it does not occur. Normal fresh urine contains little free ammonium, which is formed by bacterial decomposition of urea.
Sarcophagus-shaped crystals of a varying size. The formation of triple phosphate crystals usually is associated with a bacterial increase. The presence of triple phosphate in first morning urine specimen points to urinary tract infection. In cystitis, triple phosphate crystals generally occur along with ammonium biurate crystals.
 Bilirubin
Brown or brown-red needle-like crystals accumulated in bundles or stellate formations. Occasionally they appear as dark rhomboid plates, cubes or amorphous pellets.

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