URINARY SEDIMENT: TECHNIQUE, COMPOSITION, HISTOLOGY - BIOLOGY - 2024

The urinary sediment is the precipitate obtained on centrifuging a urine sample. It is made up of a series of formed elements, such as epithelial cells, bacteria, mucin, leukocytes, and red blood cells. These items are normal as long as they stay within the normal values.

On the other hand, the sediment may contain other components that may be transitory, but if they persist, they indicate the presence of some pathology. Example: presence of crystals.

Pathological urinary sediments. Source: Image A: J3D3 Image B: Bobjgalindo

Likewise, there are other components that should not appear under any circumstances and their mere presence indicates abnormality. Example: cereus cylinders, parasites, among others. Therefore, the characteristics of the sediment will vary according to the health status of the patient.

A normal urinary sediment contains a small amount of formed elements, which gives the urine a clear or slightly cloudy appearance.

While a pathological urinary sediment will contain exacerbated amounts of some or all of the usual formal elements and may even present additional elements that are clearly pathological. In this case the appearance of the urine will be cloudy.

The urine sediment analysis is part of the general urine test; This allows to know how the kidneys, bladder and urethra are functioning. According to what has been observed, it will be possible to know if the patient presents a normal sediment or, on the contrary, is altered.

Technique to obtain urinary sediment

Take the container of urine from the patient and mix gently. Transfer 10 ml to a centrifuge tube or a test tube. Centrifuge for 5-10 minutes at 3500 RPM.

Discard the supernatant and resuspend the urinary sediment by manual agitation. Take a drop of the resuspended pellet and place it on a clean slide, then place a coverslip on it and observe the microscope with a 40X objective immediately.

Urinary sediment can be analyzed conventionally or in an automated way.

Composition of urinary sediment

It is made up of different types of cells, mucin, casts, crystals, and microorganisms. Some elements are normal in certain amounts and others should not be present under physiological conditions.

Histology of urinary sediment

Histologically, a great variety of cells can be distinguished, which are described below.

-Red blood cells or red blood cells

The presence of red blood cells or red blood cells in the urinary sediment is normal as long as they do not exceed the number of 0-3 per field. The alteration in the amount of red blood cells in the urine is called hematuria and can vary in intensity according to the chronicity of the pathological process.

The morphology of the red blood cells is one of the most relevant data in a urinary sediment. Isomorphic and dysmorphic (postglomerular and glomerular) red blood cells can be seen respectively.

Isomorphic erythrocytes are those that retain their morphology similar to those found in the bloodstream.

Dysmorphic erythrocytes are those that have changed their normal shape, adopting distorted, deformed or fragmented morphologies, collectively known as acantocytes.

Among the types of dysmorphic erythrocytes that can be found are: multilobed, annular, empty, spiculated, among others. These can be observed in active lupus nephritis, nephrolithiasis, inflammation, glomerulonephritis, among other pathologies.

Alterations in the number of red blood cells

Microhematuria

It is called microhematuria when the amount of red blood cells observed is minimally above the normal value per field, therefore the number of red blood cells present is not enough to change the yellow color of the urine to red.

Macrohematuria

In this case, the presence of blood in the urine is macroscopically evident, that is, the urine changes its normal yellow color to a reddish color. Microscopically, abundant red blood cells per field (P / C) will be observed, which will be reported as uncountable if they exceed 30 red blood cells P / C.

Symptomatic macrohematuria can occur in cases of renal colic (lithiasis), upper or lower urinary tract infection, hemorrhagic cystitis, renal tuberculosis, interstitial nephritis, hydronephrosis, renal infarction, tumor necrosis, rupture of renal cysts, among others.

While in the asymptomatic it can occur in case of hypernephroma, neo urothelium, bladder cancer, staghorn lithiasis, treatment with anticoagulants, hydronephrosis, acute febrile processes, treatment with sulfa drugs, etc.

Red blood cells observed in the urinary sediment (hematuria). Source: Bobjgalindo

Urinary hemorrhage

It occurs when the urine is practically blood and in the urinary sediment it will be observed as if it were a blood smear.

-White blood cells or leukocytes

Leukocytes can be observed in the urinary sediment between 0-5 P / C. An alteration in the number of leukocytes may indicate infection or inflammation. Increased white blood cells in the urine is called leukocyturia.

The presence of pyocytes or scintillating leukocytes (white blood cells with granulations) is common in cases of pyolenephritis.

-Epithelial cells

The appearance of scaly epithelial cells is considered normal in a urinary sediment.

The shape of the cell indicates which anatomical site they came from. For example, small, round, polyhedral cells come from the renal tubules, while periphery, spindle, or transition cells come from the renal pelvis, ureter, or bladder.

It is normal to find scarce flat cells in men and in women it will depend on the menstrual cycle.

The presence of abundant round cells indicates kidney damage.

It should be noted that neoplastic cells can be distinguished in a urinary sediment and must be confirmed by staining the sediment with the Papanicolaou technique. Example: diagnosis of carcinoma in situ can be made.

Urine cytology, pap smear (group of slightly atypical urothelial cells). Source: myself (Alex_brollo)

-Sperm cells or sperm

In women they indicate that the urine is contaminated with semen. In men, if there has been no previous ejaculation, they may have clinical importance. It is associated with hypotonia of the ejaculatory ducts.

Presence of sperm in urinary sediment. Source: Bobjgalindo

Microorganisms in urinary sediment

The most frequent is the presence of bacteria but fungi and parasites could be found.

Bacteria

The urine should not contain bacteria, however, the observation of scarce bacteria is normal, due to the carry-over of the microorganisms found in the urethra or vagina.

Carry-over can be minimized by washing the genitals before taking the sample. Another recommendation is to take the urine sample in the middle of urination.

The number of bacteria can increase to moderate or abundant. This increase is called bacteriuria.

If there is bacteriuria without leukocyturia, it is usually due to poorly collected urine samples, that is, without proper hygiene of the genitals. The sample is said to be contaminated and is almost always accompanied by a large number of epithelial cells.

However, the presence of bacteriuria with leukocyturia indicates urinary infection. Urine culture is recommended to determine the microorganism causing the infection. It can also be accompanied by hematuria.

Parasites

Vaginal Trichomonas can be found in the urinary sediment. They are flagellated parasites that present a characteristic movement. When they are dying they can be mistaken for white blood cells.

The microfilariae and eggs of Schistosoma haematobium can appear in urine.

Eggs of Enterobius vermicularis, Ascaris lumbricoides, Giardia lamblia cysts, and Strongiloides stercoralis larvae can be found in urine contaminated with faeces.

Mushrooms

Sometimes there may be the presence of yeast in the urinary sediment, it is very common in diabetic patients. The most common is Candida albicans. Pseudohyphae can also be seen.

Mucin or mucus

Mucin occurs as thin, wavy, irregular filaments that vary in length. Its scarce or moderate presence is physiological. It can be increased in inflammatory processes or in infections. It is produced by the cells of the genitourinary tract.

Cylinders

They are elongated microscopic structures that take the shape of the renal tubule where they have formed (distal contouring or collectors), hence the name of cylinders. These when detached appear in the urine.

The casts are made of protein gels. They are a combination of mucopolysaccharides and Tamm-Horsfall protein secreted by the renal tubules that are condensed by acidity and increased dialysable elements.

The presence of casts in the urine is not normal, its appearance is due to some anomaly. Therefore, with the exception of hyaline casts that occasionally appear, all cast types are pathological.

There are thin and thick cylinders. The thin ones are due to the reduction of the width of the tubules due to inflammation of the tubular cells. Whereas, the wide or thick ones are due to the dilation of the Bellini ducts, at the entrance of the renal pelvis.

These casts can appear in renal failure and diffuse nephropathy. Depending on the composition of the cylinder, it can guide in relation to the intensity of the injury.

Hyaline cylinders

They originate from various causes. Among them are: increased permeability of glomerular membranes, due to decreased tubular resorption, alterations in protein composition and increased glomerular filtration.

Its clinical importance is similar to the presence of albuminuria. They are the most benign. They can appear occasionally in dehydrated patients or patients with physiological stress. Rarely is it due to severe kidney disorders. Its appearance is transparent.

Fatty or lipoid casts

Its presence indicates that there is an exaggerated permeability of the glomerulus. It is typical of lipoid nephritis, nephrotic syndrome, or hypothyroidism. They are basically hyaline casts with globular fat inclusions.

Granular or grainy cylinders

These are always pathological. Its presence is due to cellular degeneration in the renal tubules. These can be thin, thick or brown. They appear abundantly in glomerulonephritis and chronic nephrosis.

The increase of this type of casts in the urine in diabetics with ketosis is of a poor prognosis, since they precede coma.

Red blood cell or blood cell casts

They appear in cases of hematuria originating from the renal parenchyma and their presence rules out hematuria originating from the ureters. The cylinder contains red blood cells, the cylinders are orange red. They are generally due to the presence of pathology, however, they can appear physiologically in contact athletes.

Renal tubular epithelial casts

Composed of a mucoprotein matrix including tubular renal cells. Its presence is frequent in glomerulonephritis, in acute tubular injury (tubular necrosis) and nephrotic syndrome. Also in viral diseases such as cytomegalovirus, as well as in kidney transplant rejections.

Waxy or waxy cylinders

Its appearance is of poor prognosis, it indicates urinary stasis, since they are the result of advanced degenerative processes in the renal tubules (atrophic tubules). They appear in advanced chronic nephritis, dermatomyositis, amyloidosis, lupus, and coma. They are refractive in appearance and have irregular or fractured edges.

White or leukocyte cell casts

These types of casts are abundant in pyelonephritis (acute infections) and in interstitial nephritis.

Hemoglobin cylinders

They are typical of post-transfusion hemoglobinuria. They generally present together with granular and hematic casts.

Mixed cylinders

These cylinders are a combination of others. For example, they are composed of a protein matrix and can contain various mixed elements, such as leukocytes, red blood cells, and tubular cells. It is common in proliferative glomerulonephritis.

Pigmented cylinders

They are casts of tubular or granular cells that contain a particular coloration due to certain pathologies that release substances that are normally within muscle cells, such as myoglobin and creatine phosphokinase (rhabdomyolysis).

On the other hand, they can be presented by jaundice processes due to the increase in bilirubin. Some drugs can also cause pigmented casts, such as phenazopyridine.

Crystal cylinders

These are urinary crystals that have become embedded or entangled with hyaline casts. They are of no clinical significance.

Bacterial cylinders

They are not common to observe, since the action of leukocytes prevents their formation. They can be confused with fine grained cylinders. They usually appear in the urine accompanied by bacteriuria, leukocyturia, and leukocyte casts.

Pseudocylinders

They are cellular or mineral structures that, when going through the centrifugation process, unite and simulate the shape of a cylinder. They are artifacts that have no clinical significance.

Cylindroids

They are tubular elements similar to hyaline cylinders but differ in that one of their ends ends in a point. Its composition is also different. It is made up of mucopolysaccharides from the transitional epithelium.

Crystals

They are precipitations of substances that are produced in the urine. They can appear in healthy patients sparingly and occasionally, or in patients abundantly and persistently.

The study of the same should be carried out in newly emitted urine. The observation of crystals in urine with several hours of emission is worthless.

There are several classes; those observed in acidic urine and those in alkaline urine. They may be related to nephrolithiasis and their appearance can predict the composition of the stone, however, there are cases of lithiasis without crystalluria.

The appearance of crystals can be transitory due to the consumption of certain foods, if the harmful diet persists it can cause a lithiasis.

-Crystals of acidic urine

Amorphous urate crystals

They are made up of sodium, potassium, calcium and magnesium salts. These precipitate in acidic pH.

It is typical in concentrated urine, has a granular appearance and can be pink or reddish yellow (brick dust). They increase in fevers and in patients with gout. They are of no clinical significance.

Calcium oxalate crystals

They appear in oxalic diathesis or can be of exogenous origin (diets rich in oxalic acid).

Patients with idiopathic nephrolithiasis, in addition to having oxalate crystals with sizes between 0-10 µ, have much larger ones between 20-40 µ, called calcium oxalate dihydrate (weddellite) and monohydrate (whewellite) crystals.

It is related to diabetes mellitus, liver disease, chronic kidney disease, and diseases of the nervous system. They can also appear in neutral or slightly alkaline urine.

The observation of aggregates of calcium oxalate crystals may indicate an increased risk of kidney stone formation.

Uric acid crystals

They have a variety of forms, they increase in gout disease, in patients with leukemia or with uratic diathesis. Physiologically, it increases in diets rich in meat and in dehydration. Its persistence indicates a high risk of presenting renal lithiasis. They are yellow.

Uric acid crystals in urinary sediment. Source: Wikitorre92

Hippuric Acid Crystals

They are not clinically important but are increased in liver disease. They can also appear in alkaline or neutral urine.

Cystine, Leucine, and Tyrosine Crystals

They occur in severe liver failure and in genetic disorders of amino acid metabolism.

-Alkaline urine crystals

Amorphous phosphate crystals

They appear as very fine and colorless granulations, they are not important. They are typical of neutral or alkaline urine. In large quantities they form a white precipitate.

Calcium carbonate crystals

They are colorless crystals of very small size and if they are grouped they form large masses.

Calcium phosphate crystals

These are shaped like a needle with a sharp point, sometimes crisscrossing and simulating a star. They are colorless.

Triple phosphate crystals

Made up of calcium, ammonium and magnesium phosphate. It is common in patients with prostatic adenoma, bladder infections, and urethral stricture. They have a characteristic coffin shape.

-Other types of crystals of clinical importance

Crystals of cholesterol, bilirubin and sulfonamides. The first two indicate pathology and the third appears due to treatment with this type of drug.

Final thoughts

Transient pathological sediments can be obtained if the patient collects the urine sample after a day of intense exercise or if the patient has been subjected to severe cold. In this case, the sampling must be repeated.

Normal values ​​of the elements of the urinary sediment. Source: Valdivieso A. Hematuria. Nephrology Department. 2008.

References

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