Crystals found in Urine

Crystals are divided into two categories depending on whether they are found in 

acid (<7) pH or alkaline (>7) pH.

Types of Crystals:

Normal Crystals in Acidic Urine

Uric Acid:

 It is seen in acidic urine and pH must be <5.8 to form uric acid crystals

 Typically coloured either yellow or reddish-brown, but may be colourless. 

 Often seen as a four-sided plate that may be thin or thick and laminate. Crystals

may cluster into rosettes.

 Other forms are rhombic plates or prisms, barrel-shaped, thick cubes, oval forms

with pointed lemon-shaped ends, and wedges. Occasionally, colourless six-sided

forms resembling cystine are seen.

 Strongly birefringent when viewed with polarized microscopy 

Calcium Oxalate:

 Seen in an acid environment, but may also be found in neutral or alkaline

urine

 Small and colourless. Large forms are uncommon.

 Dihydrate crystals are the most commonly seen. Appear as an envelope or square with a cross.

 Monohydrate crystals are less commonly seen. They are ovoid,

oval, or dumbbell shape and are usually small

 Strongly birefringent when viewed with polarized microscopy

Normal Crystals in Alkaline Urine

Triple Phosphate (Ammonium Magnesium Phosphate):

 Most commonly appear as colourless 3-6 sided prisms (coffin lids)

 Size can vary greatly from tiny to relatively huge

 It May be present in neutral urines as well

 Birefringent when viewed with polarized microscopy

 Little clinical significance

Ammonium Biurate: 

 Yellow-brown spheres with striations on the surface

 It May have irregular projections or spicules, giving a “thorn apple” appearance

 Rarely seen in freshly voided urine. Often present after prolonged refrigerator

storage.

Calcium Carbonate: 

 Small, colourless granular crystals

 Slightly larger than amorphous material

 Birefringent with polarized microscopy

 Usually in pairs, giving them a dumbbell shape. 

Calcium Phosphate: 

Dibasic forms:

 Colourless, thin, wedge-like prisms arranged in small groupings or in a rosette pattern

 Each prism has one tapered or pointed end and another end is squared off

 It May appears as thin, long needles arranged in bundles or shelves 

Monobasic forms:

 Irregular, granular sheets or flat plates

 Resemble large degenerating squamous epithelium

 Weakly birefringent under polarized microscope

 Can float on top of urine and resemble a type of “scum”

Amorphous crystals:

Do not have shape or form. Amorphous urates and phosphates appear as small, 

yellow-brown granules with a sand appearance.

Amorphous urates are found in acid urine with a pink-orange precipitate

Amorphous phosphates are found in alkaline urine with a white precipitate

Refrigeration enhances the deposition of both. Both are clinically insignificant.