Rare crystals

Cystine

The cystine is seen as colorless hexagonal plates. The solubility of the cystine is much larger in alkaline urine, with the result that the former is rarely found in alkaline urine. These colorless crystals can be difficult to distinguish from the hexagonal plate form of uric acid crystals. But, in this case, the examination of the crystals under polarized light will probably show birefringent crystals with a polarization color interference.
Cystine crystals is a clinically significant finding.
A confirmatory test is described elsewhere.

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Leucine et tyrosine

Crystals of the amino acids leucine and tyrosine are very rarely seen in a urinary sediment. These crystals can be observed in some hereditary diseases like tyrosinosis and the "Maple syrup disease", but these conditions are very rare. The majority of cases where one finds these crystals are in patients with a serious hepatic problem, often in a terminal stage. In these cases, a concurrent presence of leucine and tyrosine is observed.

Leucine The leucine crystals are seen as yellow spheres with concentric and radial strias. These crystals can sometimes be mistaken with cells, the central part simulating a nucleus. Under polarized light, the former presents a maltese cross interference pattern.

Tyrosine Tyrosine crystallizes as brown neddles, isolated or forming a dense rosette.

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Bilirubin

Bilirubine crystallizes in the urine as fine needles that regroup in a clump or as red brown spheres. The clinical meaning is the same as the bilirubin detected with the dipstick.

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Cholesterol

Cholesterol crystallizes as thin rectangular plates with one of the corners (sometimes two or more) having a square notch. These crystals are very slightly birefringent. The cause of the presence of crystallized cholesterol is obscure. These crystals are seen in degenerative kidney diseases and are thought to have an identical clinical meaning as oval fat bodies. The presence of these crystals is normally accompanied by a heavy proteinuria. These crystals are very rare.

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Hemosiderin

In a case of intravascular hemolysis, a part of the free hemoglobin passes through the glomerule. The former is then reabsorbed by the tubular cells. The hemoglobin is then concentrated and transformed slowly to a deep red brown pigmented granules, the hemosiderin. These hemosiderin granules can be seen free, inside tubular cells, and embedded in a cast. The free granules agglomerate forming amorphous red brown deposit. A staining procedure, based on the Roux reaction (Prussian blue), is possible for the urinary sediment.

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Ammonium biurates

The ammonium biurates, also called acid ammonium urates, crystallize as a sphere with strias that reminds a dried apple. Several crystals will show characteristic ox-horn projections. The crystals are strongly birefringent. Ammonium biurates are rarely seen in a fresh specimen. The former are found in old specimens that turned alkaline.

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Calcium phosphates

The calcium phosphate crystals are also named di-calcium phosphate or hydroxyl-apatite. Its mineral name is brushite. This substance crystallizes as a long prism with one sharped end. These crystals are slightly birefringent.
Calcium phosphate crystals are found with triple phosphates and their clinical meaning is identical.

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Calcium carbonates

The calcium carbonate crystallizes as very small spheres. These spheres can be found alone, in pair as dumbbell shape or in four units taking a cross shape. These are strongly birefringent. Calcium carbonate crystals are rare, probably because they are difficult to distinguish from amorphous phosphates. Some authors report as calcium carbonate what is recognized by others as amorphous phosphates. The reason is that this crystal is found mixed with amorphous phosphates thus forming a combined crystalluria of homogeneous appearance. The clinical meaning of the calcium carbonate is the same as amorphous phosphates.

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Calcium sulfates

Calcium sulfate crystallizes as thin plates with sharp ends. The plate can be isolated or forming a rosette. These crystals are of little clinical meaning.