Urinary Deposits in Health and Disease

The water and salt balance of our body is taken care by our kidneys through excretion of water and salts under the strict regulatory control of various hormones. The chemical and microscopic examination of urine for the evaluation of health status is a routine procedure at health centers. The abnormal excretion of biochemical substances on physical and chemical analysis of urine and presence of chemical crystals, various cell types and casts in the urine is the first alarming point about many diseases. The microscopic examination of urinary deposits would yield a valuable information about a positive or negative character. The components of the urinary deposit can be classified into three groups: 1) Chemicals as crystals or amorphous deposits, 2) Cells from the blood or urinary tract, and 3) Casts

1. Chemical substances as crystals or amorphous deposits: Some of the inorganic and organic chemical substances could be appreciated in the urine of normal people of all age groups, but some other chemicals are always associated with pathological conditions. The presence of crystals of chemical substances in the urinary deposits is influenced by acidic or alkaline reaction of the urine. Phosphates (ammonium magnesium phosphate, Calcium hydrogen phosphate and magnesium phosphate), Calcium oxalate, uric acid and urates (of Ammonium, Sodium, Potassium, Calcium and Magnesium) are most commonly detected in the urinary deposits. Other chemical substances viewed in the urinary deposits may be Calcium carbonate, Calcium sulphate, amino acids (cystine, tyrosine and leucine), hippuric acid, cholesterol, xanthine, Sulphonamide drugs and pigments like bilirubin. Phosphates are deposited in alkaline urine and get dissolved in dilute acetic acid. Calcium oxalate crystals are soluble in hydrochloric acid but uric acid crystals are not soluble in acetic acid or hydrochloric acid. Presence of red blood cells(RBCs) in the urine may give color to the deposits. The crystals of chemical substance have very typical shapes. Microscopic examination of urinary deposits by an experienced medical technologist or pathologist is needed for an accurate assessment of chemicals, cells or casts excreted in the urine. Calcium oxalate is present in some fruits and vegetables and notable among them are strawberries, rhubarb and spinach. The crystals of Tyrosine appear like tufts of needles and those of Leucine are in spherical shape. Crystals of tyrosine and leucine are seen very rarely in the cases of severe liver disease and cirrhosis. Crystals of cholesterol appear as rectangular or rhomboid plates with notched corners and occur the urine form the patients affected by some kidney disease. Sulphonamide crystals could be found in urinary deposits during treatment with such drugs. These are formed from acetyl derivatives in the urinary tract.
2. Cells: Red blood cells (RBCs) could be detected in the urinary deposits during macrohematuria (>1000 RBCs/ml of urine) as well as microhematuria (<1000 RBCs/ml of urine). Pus cells: Less than 10 leucocytes or pus cells per microlitre (µl) of urine may occur in normal urine. An increase in the number of pus cells is called pyuria and is indicative of some inflammatory disease in the urinary tract. Urine culture may help to establish the causative agent of urinary tract infection. The cells present during the acute inflammation are mainly polymorphonuclear cells. Microscopic examination of the urinary deposit is the only satisfactory test to establish the presence of pus cells. Epithelial Cells: Epithelial cells may be detected normally in urine from female patients but an increased number could be due to pathological reasons. Epithelial cells in the urine of males are normally very few in number. Epithelial cells could be from the squamous epithelium, transitional epithelium (from the bladder, prostate, ureters and pelvis of kidneys), and basal or parabasal cells. Abnormal cells such as tumor cells may also be detected in the urinary deposits. Sometimes spermatozoa may also be present in the normal urine of males.
3. Casts: Casts are formed in renal tubules whose shape these take. Subsequently the casts are pushed by the fluid along the tubules and appear in the urine. These are seen on microscopic examination of urinary deposits. The casts could be classified on the basis of their appearance under the microscope as: 1) Hyaline casts: are simplest, pale transparent and homogenous structures with cylindrical shape and do not contain cells or granules. 2) Epithelial casts: When there is tubular damage, cells from the tubular epithelium could be trapped into casts and give rise to epithelial casts. 3) Granular casts: Casts containing closely packed granules of various size and shape are generally formed due to degeneration of tubular epithelial cells and are indicative of renal disease. 4) Fatty casts: are derived from epithelial cells when fat granules are present along with granular material. Such casts are found in tubulopathy and are indicative of degeneration of tubular epithelium.

Important Points:

• Collection of urine from each kidney by ureteric catheterization and from urinary bladder may be used to locate the site of pus formation.
• Cytological examination of the first morning urine for three consecutive days should be performed to rule out any malignancy in doubtful case.
• If large number of pus cells are detected in the urine, a urine culture is advisable to rule out the infectious organism.

Albumin & Casts in Urine and Associated Renal Lesions

Urine analysis is the cheapest and routine investigation which could be of great help to the clinician to reach at a diagnosis of a complex renal disorder. Albuminuria (excretion of albumin in urine) detected on heat test of the urine and the casts detected on microscopic examination of first morning specimen of urine reveal a lot about the associated renal lesions (pathological changes in kidney). Albuminuria we know definitely to be glomerular origin, although the tubules may also play their part in its production. It seems probable that this is mainly due to the glomerular basement membrane (GBM) which separates the epithelium of the tuft from the endothelium lining the capillaries, with increase of its permeability.

Casts are the microscopic accumulations of cells or coagulated proteins or lipids. Casts if present could be detected on microscopic examination of deposit obtained after centrifugation of urine. The casts must also be traced to the glomerulus, at least the essential hyaline matrix of the cast composed of coagulated albumin. Again the tubules add their contribution in the shape of epithelial cells and fatty and granular detritus which give to the casts their characteristic appearance. Careful examination casts is as informative as blood biochemistry investigations in cases of kidney disease. The cast gives a picture of the degenerative changes in the tubules. A hyaline cast indicates slight glomerular leakage without active tubular degeneration. Cellular casts denote marked activity of the morbid process. Granular casts denote moderate activity. The admixture of red blood cells (RBCs) is a sign of glomerular hemorrhage. We find that the study of casts is of remarkable importance in assessing the prognosis of a renal disorder. As long as there is considerable activity there is a scope for improvement. For such a study to be of value, the urine should be fresh. If the urine is alkaline or has been allowed to stand for long time, the casts may largely disappear. The absence of casts in an alkaline urine has not the same significance as when the urine is acidic. The acidity of the urine assists in the formation of casts. Deposition of casts in the tubules may lead to oliguria (low output of urine) leading to edema.