Urine Analysis – part 8 – Urine Crystals (Crystalluria)
- Freshly voided urine is the best sample.
- Refrigerate or if you keep at room temperature that will increase the formation of the crystals.
- There may be well-defined crystals or amorphous material in the urine sediment.
- These appear as geometrical formed structure or amorphous material.
- The presence of crystals in the urine is called Crystalluria.
- When urine left at room temperature or refrigerated then urine becomes cloudy because of precipitation of crystals or amorphous material.
- Importance of the Crystals:
- These crystals are important in the case of kidney stones.
- Renal damage caused by the crystals.
- In liver diseases.
- Inborn error of metabolism.
- Some of the crystals indicate some metabolic disorders like cystinuria or a sulfa drug.
- The stone formation may be without crystals in the urine or crystalluria may be without stone formation.
- Crystals are seen mostly in the concentrated urine.
- Crystals are divided into :
- Normal or abnormal
- In alkaline or acidic urine.
- Crystals found due to medication.
- Crystals found in acidic urine has a pH of <6.5 and in alkaline urine pH is >7.0.
- Reporting of the crystalluria:
- Mechanism of the formation of crystals:
- Crystals formed by the crystalization of urine solutes.
- The solutes are:
- Inorganic salts.
- Organic compounds.
- Medications by drug use.
- Precipitation is dependent upon:
- Solute concentration.
- As the concentration of solutes increases, their ability to remain solution decreases and result in crystal formation.
- Solute precipitate more readily at low temperatures.
- So if you keep the urine at room temperature or refrigerate, then crystals are abundant.
- Organic and iatrogenic compounds crystalize more easily in the acid urine.
- Inorganic salts are less soluble in neutral or alkaline pH.
- The exception is calcium oxalate which precipitates in both acidic and alkaline medium.
- The Slower crystalization leads to larger crystal formation but the basic structure remains the same.
- Reversal of the pH will dissolve the crystals.
- Amorphous urates crystals formed in the refrigerated sample, if you warm the urine these will disappear.
- Amorphous phosphate crystals need acetic acid to dissolve. But practically this is not done because the acetic acid will distort the RBCs.
- Helping point in Reporting of the crystals:
- Always note the pH of the urine which will help to identify the crystals.
- All abnormal crystals are found in the acidic urine.
- Polarized microscopy also helps to identify the crystals.
- Characteristics of crystals:
- Most of the urate crystals are yellow to reddish-brown.
- Amorphous urates appear yellow-brown granules. these are in clumps and looks like the granular cast.
- If urine refrigerated then the amorphous urates crystals precipitate and give pink sediment.
- Amorphous urates crystals appear in the urine with low pH >5.5 and uric acid crystals appear when pH is lower.
Various types of crystals in acid urine:
- Uric acid:
- These are seen in a variety of shapes like four-sided flat plates, wedge-shaped, and rosettes.
- These are usually yellow-brown in color.
- But maybe colorless and six-sided shapes like cystine crystals.
- these are birefringent in polarized light.
- These are common in patients with leukemia getting chemotherapy.
- Sometimes these are seen in gout.
- Acid urates and sodium urates:
- These are like amorphous urates and seen in less acidic urine.
- These are seen along with amorphous urates and have little clinical significance.
- Sodium urates crystals are needle-shaped and are seen in the synovial fluid during the attack of gout and also appear in the urine.
- Amorphous urates:
- These are yellow-brown granules.
- These may appear in clumps resembling granular cast.
- These crystals are found in acidic urine with pH>5.5.
- Calcium oxalate:
- More common in acid urine, but may be seen in neutral or even in alkaline urine.
- Most common is dihydrate, are colorless, octahedral envelope shape or two pyramids joined together at their bases.
- Monohydrate crystals are oval or dumble shaped.
- In polarized light both are birefringent.
- The finding of clumps of calcium oxalate crystals indicates the renal stone formation.
- These are commonly seen when taking foods like tomato, asparagus, and ascorbic acid.
- Monohydrate crystals are seen in the ethylene glycol (antifreeze) poisoning.
Crystals in the acidic urine :
|Name of crystals||pH||Effect of heating (solubility)||Shape||Color|
|Sodium urate||acidic (<acidic)||soluble at 60 C||amorphous||Amorphous, or large granules|
|Uric acid||acidic <5.5||alkali-soluble||rhombic, four-sided flat plates||yellow-brown|
|Amorphous urates||acidic >5.5||alkali and heat||amorphous or sand-like||Microscopically yellow-brown and occurs in clumps|
|Calcium oxalate||acidic or alkaline||dilute HCL||enveloped shaped, dumbbell-shaped||The colorless octahedral envelope or two pyramids joined at the base.|
|Cystine||acidic||Dilute HCl acid||hexagonal||Colorless|
|Cholesterol||acidic||Chloroform||rectangular, notched plates||Colorless|
|Tyrosine||acid/neutral||Alkali or heat||needles shape form clumps or rosettes||Colorless to yellow, needles|
|Leucine||acidic /neutral||Hot alkali or alcohol||spheres with a concentric circle or radial striations||yellow-brown|
Acetic acid, HCL,
ether or chloroform
|clumped needles or granular||yellow color|
|Sulphonamide||acid/neutral||Acetone||Rosette form, needle,||colorless to yellow-brown|
|Ampicillin||acid/neutral||in needles form||colorless|
|Radiographic dye||acid||10% NaOH||like cholesterol||colorless|
Various types of crystal in alkaline urine:
- Amorphous phosphate:
- These are granular in shape like amorphous urates.
- If refrigerated then these produce white precipitate which does not dissolve on warming.
- These are differentiated from the urates by color and the pH of the urine.
- Tripple phosphate (Ammonium magnesium phosphate):
- These are seen in alkaline urine.
- These are colorless, prism-shaped, resembling the coffin lid.
- Under polarized lights are birefringent.
- These have no clinical significance.
- Calcium phosphate:
- These are colorless, flat rectangular plates.
- Or thin prism and often in rosette forms.
- Rosette forms need to be differentiated from the sulphonamides crystals.
- These crystals dissolve in dilute acetic acid while sulphonamides crystals will not.
- These have no clinical significance.
- Calcium carbonate:
- These are small. colorless, with a dumbbell or spherical shapes.
- These may occur in clumps and resemble amorphous material.
- If you add acetic acid, then there is gas formation.
- In polarized light are birefringent and this differentiates from the bacteria.
- Thes crystal has no clinical significance.
- Ammonium biurates:
- These have characteristic yellow-brown color.
- These are usually described as thorny apples, because of the spicule-covered spheres.
- These dissolve at 60 °C.
- If you add glacial acetic acid, then these will change into uric acid.
Crystals in alkaline urine :
|Name of crystals||pH||Effect of heat||Color and shape|
|Amorphous phosphates||Alkaline||Remain insoluble||Granular|
|Triple phosphates||Alkaline||Colorless and prism-shaped like a coffin lid|
|Calcium phosphate||Alkaline||Remain insoluble||Colorless, flat rectangular plates or thin prisms often in rosettes|
|Calcium Carbonate||Alkaline||Small, colorless with a dumbbell or spherical shape, may occur in clumps and resemble amorphous material|
|Ammonium biurate||Alkaline||Dissolve at 60 °C||Yellow-brown color, thorny apples|
The solubility of crystals:
|Calcium oxalate||Colorless||Acid/neutral||Dilute HCl acid|
|Amorphous urates||Brick dust or yellow-brown||Acid||Alkali and when heated|
|Tripple phosphate||Colorless||Alkaline||Dilute acidic acid|
|Amorphous phosphate||White-colorless||Alkaline/neutral||Dilute acid acid|
|Calcium phosphate||Colorless||Alkaline/neutral||Dilute acidic acid|
|Calcium carbonate||Colorless||Alkaline||Acetic acid|
|Ammonium biurate||Yellow-brown||Alkaline||Acetic acid with heat|
- Metabolic origin:
- Drugs origin:
- Radiographic contrast media.
- Metabolic origin:
- These are seen in the inborn error metabolic disorder when the cystine is not absorbed by the renal tubules (cystinuria).
- There is a tendency to form renal calculi.
- These are colorless, hexagonal plates and may be thick or thin.
- In the presence of ammonia, there is the disintegration of these crystals.
- Cyanide-nitroprusside test needed to confirm the cystine crystals.
- These are not seen unless the urine is refrigerated.
- These have a characteristic appearance resembling the rectangular plates with a notch in one or more corners.
- These are seen disorder producing lipiduria in nephrotic syndrome, along with fatty acids and oval fat bodies.
- In polarized light, these are birefringent.
- There are a variety of crystals shapes and colors.
- Shapes variable like needles, whetstone, rhombic, wheat, and rosette with color ranging colorless to yellow-brown,
- The history of the patient will help you to diagnose these crystals.
- Diazo reaction can confirm these crystals.
- These are fine colorless to yellow needles like structure which form clumps or rosettes.
- These may be seen in inherited disorders of amino acid metabolism.
- These are seen because of the defect in amino acid, leucine.
- These are yellow-brown spheres that will show concentric circles and radial striations.
- These are also called wagon wheels.
- These are soluble in hot alcohol and alkali.
- These are less frequent than the tyrosine crystals.
- These are accompanied by tyrosine crystals.
- Bilirubin crystals are present in liver diseases where there is an increased amount of the bilirubin excreted in the urine.
- These crystals are clumped needles or granules with the characteristic color of the bilirubin as yellow.
Chemicals reaction for the bilirubin is positive.
Significance of crystals:
- Calcium oxalate crystals in clumps indicate renal stone formation.
- Calcium oxalate crystals are abundant in the food with high oxalic acid like tomatoes, asparagus, and ascorbic acid.
Monohydrate oxalate crystals are seen in ethylene glycol poisoning (antifreeze material).
Contamination and artifacts:
There are few contaminants that interfere with the microscopy of the sediments like:
- Fibers including diaper fibers.
- Oil droplets.
- Air bubbles.
- Pollin grains.
- Fecal contamination.
- Glass fragments.