Introductions of Common Urinary Casts

Urinary or urine casts in urine routine examination are completed in the following steps- First request the patient to bring a urine specimen. After the arrival of the specimen in the clinical laboratory, take nearly 5 ml of urine and centrifuge it. Put a drop of the mixed sediment part on a clean and grease-free glass slide and place a coverslip over it. Examine the entire 22- by 22-mm coverslip systematically with the low power objective (10X ) and low light intensity. If any suspicious objects are encountered, examine them with the high dry objective (40X). The common urinary casts faced during urine microscopy are hyaline casts, granular casts, fatty casts, waxy casts, white blood cell casts/WBC casts, bacterial casts, and crystal casts.

Identification Features, and Clinical Significance of Urine Casts-

Hyaline casts

The hyaline cast is a type of urinary cast that is simple and most commonly found, which is a cluster of urinary particles, such as cells, fat bodies, or microorganisms, held together by a protein matrix and found in the urine. It can be seen in both healthy and pathological conditions.

Identification Features

Appear as clear, tiny tubule-shaped particles

Clinical Significance

Not a dangerous finding, Strenuous exercise, diuretic medications, severe vomiting, or fever. But large amounts of hyaline casts may indicate kidney damage due to decreased blood flow to the kidneys.

Granular Cast

The granular cast is a cast that contains either proteins, tubular cells, or leukocytes that have broken down.

Clinical Significance

Exercise or dehydration, acute tubular necrosis.

Fatty Cast

It is formed by the breakdown of lipid-rich epithelial cells, these are hyaline casts free globules of fat or oval fat bodies inclusions, yellowish-tan in color.

Identification Features

There is the presence of refractile lipid droplets within the protein matrix of the cast.

Clinical Significance

Fatty cast in urinary sediment is faced in various clinical conditions like high urinary protein nephrotic syndrome, diabetic or lupus nephropathy or toxic renal poisoning, or larger-scale necrosis or epithelial cell death.
Stain: Fatty cast has globules of fat, either as triglyceride or neutral fat, that stains with fat stain, or as cholesterol, which will unify as a Maltese cross.

Waxy Cast

It is a form of urinary cast consisting of homogeneous proteinaceous material that has a high refractive index, in contrast to the low refractive index of hyaline casts; waxy casts probably represent an advanced stage of the disintegrative process that results in coarsely and finely granular casts and are usually indicative of advanced renal disease.

Identification Features

Broken off or blunt ends, notched and sharp margins, lateral cracks, high refractive index, and a surface whose appearance is reminiscent of that of melted wax.

Clinical Significance

Amyloidosis, post-infectious glomerulonephritis, and frequent association in increased levels of serum creatinine

White blood cells (WBC) Cast

White blood cell casts or WBC casts in routine urinalysis refer to a hyaline matrix cast bearing neutrophil inclusions.

Identification Features

WBCs in a cast

Clinical Significance

Tubular disease, especially infection and acute pyelonephritis

Crystal Casts

Crystal Casts are crystallized urinary solutes, such as oxalates, urates, sulphonamides, etc., that may become enmeshed within a ketanaline cast during its formation.

Identification Features

Crystals in a cast

Clinical Significance

They show little clinical significance.

RBC Cast

RBC casts in routine urinalysis refer to a hyaline matrix cast bearing erythrocyte inclusions.

Identification Features

RBCs in a cast

Clinical Significance

RBC casts are seen in glomerular disease, acute glomerulitis, renal infarction, severe pyelonephritis, and subacute bacterial endocarditis.

Epithelial Casts

Composed of renal epithelial cells

Identification Features

Renal epithelial cells in a cast

Clinical Significance

They are involved in acute tubular necrosis, viral diseases such as infection with cytomegalovirus, and exposure to nephrotoxic substances such as mercury, ethylene glycol, and drugs.

Keynotes on Urine Casts

• WBC cast is stained with Naphtyl AS-D chloro-acetate esterase.
  A cellular cast may be composed of any of the cells found in the urine sediment, such as WBC, RBC, or renal tubular epithelial cells.
• Myoglobin casts are clinically significant because they occur with myoglobinuria as a result of acute muscle damage, which may result in acute renal failure.
• RBC/erythrocyte casts are most associated with glomerular disease, whereas WBC casts are indicative of tubular disease, particularly infection and acute pyelonephritis.
• Casts encountered in the urine sediment are hyaline casts, granular casts, fatty casts, waxy casts, cellular casts (WBC, RBC, Epithelial casts), bacterial casts, and crystal casts.