Cylinders in Urine: What are they? Where are they formed? Composition, Types and Clinical Significance

The urine test has been used as a complementary diagnostic method since the 2nd century.

The casts in the urine are detected through a urine test.

It’s a painless exam, a simple collection, and a quick result, making it much less painful than blood tests, which can only be collected through needles.

Urinalysis can provide important clues about diseases, especially kidney and urinary problems.

The presence of blood, pus, protein, glucose, and various other substances in the urine is often important advice for conditions that do not yet have very clear signs or symptoms.

Just because urine looks completely normal doesn’t mean it can’t contain changes. Even the presence of blood may only be microscopic, and it cannot be identified by any means other than laboratory examination of urine.

Definition of urinary casts and where they form

Urinary casts are small tube-shaped particles made up of white blood cells, red blood cells, or kidney cells.

They form in the ascending limb of the loop of Henle and in the distal tubules due to acidity, peak solute concentration, secretion of Tamm-Horsfall mucoproteins, and slow urine flow. This region of the nephron.

The basic components of these casts are the Tamm-Horsfall mucoproteins. Therefore, a large cylindruria is a manifestation of a kidney problem (often acute).

The number of cylinders does not indicate the reversibility or irreversibility of the condition. The presence of some hyaline and granular casts may be normal. Cylinders are classified according to their composition.

Hyaline casts are exclusively made up of Tamm-Horsfall mucoproteins. They dissolve rapidly in very dilute urine (<1.003) and at alkaline pH. They are transparent and can be seen in large amounts during proteinuria.

Proteins, as well as epithelial cells, white blood cells (leukocytes), red blood cells (erythrocytes), and fat particles, can accumulate in the kidney tubules in kidney disorders. They cover the renal tubules from the inside, as if they were fused or forming casts.

Urinary casts appear in the urine only if they contain protein, because protein acts as an adhesive substance. The presence of gypsum in the urine is defined as cylindruria.

Urinary casts do not dissolve if the urine is acidic. If it is alkaline, they do not form at all or dissolve quickly. Therefore, little or no gypsum in alkaline urine may not reflect the true state of affairs.

Urinary cylinders can come in different shapes, colors, and sizes, depending on their composition. As a result, not only the amount of urinary plaster but also its type is indicated in the urinalysis.

Composition and types of cylinders

Hyaline casts are composed only of proteins. They can be detected in the urine in proteinuria (amount of protein in the urine), even if there is no damage to the kidneys (physiological proteinuria), as well as in all kidney diseases associated with elevated levels of protein in the urine (glomerulonephritis, pyelonephritis , interstitial nephritis).

Granular cylinders

They are protein casts of renal tubules with disintegrated or regenerated epithelial cells of renal tubules, adhered to their surfaces and thus giving the molds their granular shape.

Granular casts can be found in diseases associated with damage to the renal tubules and proteins in the urine (acute and chronic glomerulonephritis, diabetic nephropathy, renal amyloidosis, pyelonephritis, viral infection with fever).

Waxy cylinders

They are formed from hyaline and granular molds that remain in the renal tubules. They are composed of an unstructured mass that resembles wax.

As a rule, waxy casts in the urine are indicative of severe kidney damage or advanced chronic kidney disease. Waxy casts are considered a negative prognostic indicator.

Red blood cell casts (RBC)

They are made from proteins and red blood cells (erythrocytes). They are often not detected in the urine due to their fragility.

Red blood cell casts indicate the renal origin of hematuria (red blood cells in urine). Found in acute glomerulonephritis, renal infarction, renal vein thrombosis, diabetic nephropathy, renal tuberculosis, kidney tumors.

White blood cell casts (WBC)

They are made of proteins and white blood cells (leukocytes). They are quite rare and are more common with acute kidney infections (pyelonephritis).

Epithelial cell casts

They are made up of exfoliated renal tubular epithelial cells. Its presence in the urine indicates pathological processes in the kidneys. Most often, they are detected in the urine in nephrosis and acute nephritis.

Epithelial cell casts found in the urine a few days after surgery indicate kidney transplant rejection.

What do the cylinders indicate in the urine?

The cylinders that can indicate a problem are:

  • Hematologic (blood) casts : indicate glomerulonephritis .
  • White blood cell casts : indicate inflammation of the kidneys.
  • Epithelial casts : indicate lesions of the tubules.
  • Fatty or waxy casts : indicate proteinuria .

Hyaline casts do not indicate disease, but may be a sign of dehydration.