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 sample collection, and a quick result, making it much less painful than blood tests, which can only be collected through needles.
Urinalysis can provide essential 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 obvious signs or symptoms.
Just because urine looks 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 of white blood cells, red blood cells, or kidney cells.
They form in the ascending limb of the loop of Henle and the distal tubules due to acidity, peak solute concentration, secretion of Tamm-Horsfall mucoproteins, and slow urine flow. This region of the nephron.
The essential components of these casts are the Tamm-Horsfall mucoproteins. Therefore, a large cylindruria manifests as 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 regular. Cylinders are classified according to their composition.
Hyaline casts are exclusively made up of Tamm-Horsfall mucoproteins. They dissolve rapidly in dilute urine (<1.003) and at alkaline pH. They are transparent and can be seen in large amounts during proteinuria.
Proteins and 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 is 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 or dissolve quickly. Therefore, little or no gypsum in alkaline urine may not reflect the actual state.
Urinary cylinders can come in different shapes, colors, and sizes, depending on their composition. As a result, the amount of urinary plaster and 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).
They are protein casts of renal tubules with disintegrated or regenerated epithelial cells adhered to their surfaces, 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).
They are formed from hyaline and granular molds in the renal tubules. They are composed of a shapeless mass that resembles wax.
As a rule, waxy casts in the urine indicate 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, and kidney tumors.
White blood cell casts (WBC)
They are made of proteins and white blood cells (leukocytes). They are rare and more familiar 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. They are often 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 releases: indicate inflammation of the kidneys.
- Epithelial casts: indicate lesions of the tubules.
- Fatty or waxy casts: indicate proteinuria.