MICROSCOPIC URINALYSIS A properly collected clean-catch, midstream urine after cleansing of the urethral meatus is adequate for complete urinalysis. In fact, these specimens generally suffice even for urine culture. A period of dehydration may precede urine collection if testing of renal concentration is desired, but any specific gravity > 1.022 measured in a randomly collected specimen denotes adequate renal concentration so long as there are no abnormal solutes in the urine. Another important factor is the interval of time which elapses from collection to examination in the laboratory. Changes which occur with time after collection include: 1) decreased clarity due to crystallization of solutes, 2) rising pH, 3) loss of ketone bodies, 4) loss of bilirubin, 5) dissolution of cells and casts, and 6) overgrowth of contaminating microorganisms. Generally, urinalysis may not reflect the findings of absolutely fresh urine if the sample is > 1 hour old. Therefore, get the urine to the laboratory as quickly as possible. -------------------------------------------------------------------------------- Examination The sediment is first examined under low power to identify most crystals, casts, squamous cells, and other large objects. The numbers of casts seen are usually reported as number of each type found per low power field (LPF). Example: 5-10 hyaline casts/L casts/LPF. Since the number of elements found in each field may vary considerably from one field to another, several fields are averaged. Next, examination is carried out at high power to identify crystals, cells, and bacteria. The various types of cells are usually described as the number of each type found per average high power field (HPF). Example: 1-5 WBC/HPF. -------------------------------------------------------------------------------- Red Blood Cells Hematuria is the presence of abnormal numbers of red cells in urine due to: glomerular damage, tumors which erode the urinary tract anywhere along its length, kidney trauma, urinary tract stones, renal infarcts, acute tubular necrosis, upper and lower urinary tract infections, nephrotoxins, and physical stress. Red cells may also contaminate the urine from the vagina in menstruating women or from trauma produced by bladder catheterization. Theoretically, no red cells should be found, but some find their way into the urine even in very healthy individuals. However, if one or more red cells can be found in every high power field, and if contamination can be ruled out, the specimen is probably abnormal. RBCs may appear normally shaped, swollen by dilute urine (in fact, only cell ghosts and free hemoglobin may remain), or crenated by concentrated urine. Both swollen, partly hemolyzed RBCs and crenated RBCs are sometimes difficult to distinguish from WBCs in the urine. In addition, red cell ghosts may simulate yeast. The presence of dysmorphic RBCs in urine suggests a glomerular disease such as a glomerulonephritis. Dysmorphic RBCs have odd shapes as a consequence of being distorted via passage through the abnormal glomerular structure. Red blood cells in urine Dysmorphic red blood cells in urine -------------------------------------------------------------------------------- White Blood Cells Pyuria refers to the presence of abnormal numbers of leukocytes that may appear with infection in either the upper or lower urinary tract or with acute glomerulonephritis. Usually, the WBCs are granulocytes. White cells from the vagina, especially in the presence of vaginal and cervical infections, or the external urethral meatus in men and women may contaminate the urine. If two or more leukocytes per each high power field appear in non-contaminated urine, the specimen is probably abnormal. Leukocytes have lobed nuclei and granular cytoplasm. White blood cells in urine -------------------------------------------------------------------------------- Epithelial Cells Renal tubular epithelial cells, usually larger than granulocytes, contain a large round or oval nucleus and normally slough into the urine in small numbers. However, with nephrotic syndrome and in conditions leading to tubular degeneration, the number sloughed is increased. When lipiduria occurs, these cells contain endogenous fats. When filled with numerous fat droplets, such cells are called oval fat bodies. Oval fat bodies exhibit a Maltese cross configuration by polarized light microscopy. Oval fat bodies in urine Oval fat bodies in urine, with polarized light Transitional epithelial cells from the renal pelvis, ureter, or bladder have more regular cell borders, larger nuclei, and smaller overall size than squamous epithelium. Renal tubular epithelial cells are smaller and rounder than transitional epithelium, and their nucleus occupies more of the total cell volume. Squamous epithelial cells from the skin surface or from the outer urethra can appear in urine. Their significance is that they represent possible contamination of the specimen with skin flora. Squamous epithelial cells in urine -------------------------------------------------------------------------------- Casts Urinary casts are formed only in the distal convoluted tubule (DCT) or the collecting duct (distal nephron). The proximal convoluted tubule (PCT) and loop of Henle are not locations for cast formation. Hyaline casts are composed primarily of a mucoprotein (Tamm-Horsfall protein) secreted by tubule cells. The Tamm-Horsfall protein secretion (green dots) is illustrated in the diagram below, forming a hyaline cast in the collecting duct: Even with glomerular injury causing increased glomerular permeability to plasma proteins with resulting proteinuria, most matrix or glue that cements urinary casts together is Tamm-Horsfall mucoprotein, although albumin and some globulins are also incorporated. An example of glomerular inflammation with leakage of RBCs to produce a red blood cell cast is shown in the diagram below: The factors which favor protein cast formation are low flow rate, high salt concentration, and low pH, all of which favor protein denaturation and precipitation, particularly that of the Tamm-Horsfall protein. Protein casts with long, thin tails formed at the junction of Henles loop and the distal convoluted tubule are called cylindroids. Hyaline casts can be seen even in healthy patients. Red blood cells may stick together and form red blood cell casts. Such casts are indicative of glomerulonephritis, with leakage of RBCs from glomeruli, or severe tubular damage. White blood cell casts are most typical for acute pyelonephritis, but they may also be present with glomerulonephritis. Their presence indicates inflammation of the kidney, because such casts will not form except in the kidney. When cellular casts remain in the nephron for some time before they are flushed into the bladder urine, the cells may degenerate to become a coarsely granular cast, later a finely granular cast, and ultimately, a waxy cast. Granular and waxy casts are be believed to derive from renal tubular cell casts. Broad casts are believed to emanate from damaged and dilated tubules and are therefore seen in end-stage chronic renal disease. The so-called telescoped urinary sediment is one in which red cells, white cells, oval fat bodies, and all types of casts are found in more or less equal profusion. The conditions which may lead to a telescoped sediment are: 1) lupus nephritis 2) malignant hypertension 3) diabetic glomerulosclerosis, and 4) rapidly progressive glomerulonephritis. In end-stage kidney disease of any cause, the urinary sediment often becomes very scant because few remaining nephrons produce dilute urine. Hyaline casts in urine Red blood cell casts forming in tubules Red blood cell cast in urine White blood cell cast in urine Renal tubular cell cast in urine Granular casts in urine Granular cast in urine Waxy cast in urine Bile stained hyaline casts in renal tubules -------------------------------------------------------------------------------- Bacteria Bacteria are common in urine specimens because of the abundant normal microbial flora of the vagina or external urethral meatus and because of their ability to rapidly multiply in urine standing at room temperature. Therefore, microbial organisms found in all but the most scrupulously collected urines should be interpreted in view of clinical symptoms. Diagnosis of bacteriuria in a case of suspected urinary tract infection requires culture. A colony count may also be done to see if significant numbers of bacteria are present. Generally, more than 100,000/ml of one organism reflects significant bacteriuria. Multiple organisms reflect contamination. However, the presence of any organism in catheterized or suprapubic tap specimens should be considered significant. -------------------------------------------------------------------------------- Yeast Yeast cells may be contaminants or represent a true yeast infection. They are often difficult to distinguish from red cells and amorphous crystals but are distinguished by their tendency to bud. Most often they are Candida, which may colonize bladder, urethra, or vagina. -------------------------------------------------------------------------------- Crystals Common crystals seen even in healthy patients include calcium oxalate, triple phosphate crystals and amorphous phosphates. Very uncommon crystals include: cystine crystals in urine of neonates with congenital cystinuria or severe liver disease, tyrosine crystals with congenital tyrosinosis or marked liver impairment, or leucine crystals in patients with severe liver disease or with maple syrup urine disease. Oxalate crystals in urine Triple phosphate crystals in urine Cystine crystals in urine -------------------------------------------------------------------------------- Miscellaneous General crud or unidentifiable objects may find their way into a specimen, particularly those that patients bring from home. Spermatozoa can sometimes be seen. Rarely, pinworm ova may contaminate the urine. In Egypt, ova from bladder infestations with schistosomiasis may be seen.
Posted on: Tue, 12 Aug 2014 17:07:44 +0000
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