things such as RBCs or WBCs can become trapped in the protein as the cast is formed. When this happens, the cast is identified by the substances inside it, for example, as a red blood cell cast or white blood cell cast. Different types of casts are associated with different kidney diseases, and the type of casts found in the urine may give clues as to which disorder is affecting the kidney. Some other examples of types of casts include granular casts, fatty casts, and waxy casts.
Normally, healthy people may have a few (0–5) hyaline casts per low power field (LPF). After strenuous exercise, more hyaline casts may be detected. Cellular casts, such as RBC and WBC casts, indicate a kidney disorder.
Urine contains many dissolved substances (solutes) – waste chemicals that the body needs to eliminate. These solutes can form crystals, solid forms of a particular substance, in the urine if:
- The urine pH is increasingly acidic or basic;
- The concentration of dissolved substances is increased; and
- The urine temperature promotes their formation.
Crystals are identified by their shape, color, and by the urine pH. They may be small, sand-like particles with no specific shape (amorphous) or have specific shapes, such as needle-like. Crystals are considered "normal" if they are from solutes that are typically found in the urine. Some examples of crystals that can be found in the urine of healthy individuals include:
- Amorphous urates
- Crystalline uric acid
- Calcium oxalates
- Amorphous phosphates
- Calcium carbonate
If the crystals are from solutes that are not normally in the urine, they are considered "abnormal." Abnormal crystals may indicate an abnormal metabolic process. Some of these include:
When crystals form as urine is being made in the kidney, they may group together to form kidney "stones" or calculi. These stones can become lodged in the kidney itself or in the ureters, tubes that pass the urine from kidney to the bladder, causing extreme pain.
Medications, drugs, and x-ray dye can also crystallize in urine. Therefore, the laboratorian must be familiar with and trained in the identification of urine crystals.