Crystals found in Urine

Crystals are microscopic solids that are composed of different substances. Their formation depends on the concentration of the substances, the urine pH, and temperature. Crystals are normally not present in urine. Typically, urine crystals show limited signs and symptoms unless large enough urinary stones develop.

Types of crystals:

  • Uric acid
  • Calcium oxalate
  • Ammonium magnesium phosphate (triple phosphates or struvites)
  • Calcium phosphate
  • Ammonium urate

Urine with an acidic pH may contain uric acid and calcium oxalate crystals. For example, patients with diabetes mellitus can have acidic urine, and these crystals may be present. Uric acid crystals may also be present in patients with gout, fever, and kidney problems. Calcium oxalate crystals can be present if the patient has consumed ethylene glycol in antifreeze or has a kidney problem.

Ammonium magnesium phosphate crystals, calcium phosphate crystals, and ammonium urate crystals may appear in the patient's urine if they have a bacterial urinary tract infection caused by a urea-splitting bacteria such as Proteus. Urea-splitting bacteria do not cause all urinary tract infections. For example, E-coli does not split urea but can cause urinary tract infections, so these crystals will not always be present.

Microscope images of crystals. The uric acid crystals have a rounded diamond shape. The calcium oxalate monohydrate crystals have an hourglass shape. The calcium oxalate dihydrate crystals have a rectangular shape.

Figure 1: Different types of crystals under the microscope. A) Uric acid crystals. B) Calcium oxalate monohydrate. C) Calcium oxalate dihydrate.