Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_2617_Библиотеки_им_академика_М_И_Перельмана

eter from a clinical and laboratory point of view, with obvi­ous limitations in measuring it by dry chemistry. Urinary pH can vary from 4.5 to 7.5. The determination of pH is very important for the laboratory because it allows for better interpretation of the other chemical reactions (albumin­proteins) and correctly evaluating crystalluria and eventual bacteriuria. For the clinician, it provides important informa­tion for urinary infections and for the evaluation of tubular function. The urinary pH can inuence the conservation of the gured elements: for example, at alkaline pH, the lysis of the cells and the failure to form cylinders due to interaction with their protein matrix can occur.

Certain bacteria (mainly Enterobacteriaceae) can convert nitrates normally present in urine into nitrites. Nitrates are introduced into the body by a diet rich in fresh vegetables, and their reduction to nitrites by bacterial metabolism requires a variable amount of time depending on the amount and type of bacteria involved. Therefore, in case of lack of intake of nitrates with the diet, reduced permanence of urine in the bladder, infections by bacteria not able to reduce nitrates to nitrites, the test for nitrites in urine may be nega-

tive even during urinary tract infections (UTI). Although the test has low sensitivity, it is useful because it has a high posi­tive predictive value (PPV).

while no automated liquid chemistry kits are available.

Glycosuria occurs when the amount of ultraltrated glucose exceeds the tubular reabsorption capacity. This can occur because of a decrease in the proximal tubule’s ability to reab­sorb glucose or because of increased ultraltration due to hyperglycemia. In the subject with intact kidneys, usually, glycosuria appears when glycemia exceeds 180 mg/dL; moreover, glycosuria with normal blood glucose concentra­tion can occur in a congenital tubular pathology, known as normoglycemic glycosuria, and in nephrotic syndrome. It must be remembered that normoglycemic glycosuria can also be observed during therapy of diabetic disease with inhibitors of sodium-glucose cotransporters type 2, located in the proximal part of the convoluted tubule, which are responsible for about 90% of the reabsorption of ultral­trated glucose. Test strips can give false negatives in the pres­ence of ascorbate and in case of urinary tract infection, while false positives are observed in the presence of oxidizing sub­stances and acidic urine. The determination by liquid chem­istry using a specic enzymatic method is useful in nephrological pathologies such as congenital or acquired tubulopathies (Fanconi syndrome) and in tubulo-interstitial diseases of various etiologies. Urinary glucose testing can be included, together with ketones, in a prole dedicated to pediatric subjects in early childhood due to the more fre­quent use of urine testing as the rst test in clinical suspicion of diabetes.

Ketones are a family of three compounds—acetone, acetoac­etate, and β-hydroxybutyric acid—that derive from the metabolism (in glucose deciency) of fatty acids. The pres­ence of ketones in the urine is mostly related to fasting and is useful only in reference to specic patient populations and in specic clinical conditions (diabetes, hypothermia, fever, prolonged vomiting, fetal complications in the postterm) but

fraction of urine and the considerable related clinical impli­cations are exemplied in Table19.5. The methods of obser­vation of the urinary sediment under light microscopy, enunciated in the European guidelines of 2000, remain valid today in the general principles.

Hematuria is dened as the presence of blood cells in the urine. It is called macrohematuria if the amount of blood is

THP brils. In normal subjects, the nding of hyaline cylin­ders is not uncommon. Based on their constitution, it is pos­sible to distinguish the following types of cylinders: hyaline, granular (with small and large granules), leucocytic, erythro­cytic, epithelial (renal tubular cells), lipidic, waxy, pigmented (by hemoglobin, myoglobin, and bilirubin), with bacterial or fungal inclusions, with crystalline inclusions, or mixed.

The small granules are formed by conglutinates of ultral­trated proteins at the level of the glomerulus; the large gran­ules are formed by the degeneration of cellular elements. They are not usually found in the urine of normal subjects although, even in the absence of renal pathology, small gran­ule cylinders may be found after hyperpyrexia. Large gran­ule cylinders are often found in many types of nephropathies, such as glomerulonephritis and diabetic nephropathy. In patients with acute renal failure, granular cylinders are con­sidered a marker of organic tubular damage.

They are present in situations characterized by marked pro­teinuria, especially in nephrotic syndrome.

The presence of cylinders with bacterial inclusions suggests a renal infection; the nding is of considerable importance because it is indicative of the presence of a particularly severe infection.

cuboidal. The renal tubules are lined by the tubular epithe­lium. On a morphological basis, it is possible to distinguish the epithelium of distal and proximal tubules, monostratied with cubic or cylindrical cells, with a roundish central nucleus and short microvilli on the luminal side, from the epithelium of the collecting duct generally cubic, with an oval central nucleus and short microvilli. Epithelial cells may come from any portion of the genito-urinary tract and, therefore, are, by denition, extremely pleiomorphic.

From a morphological point of view, there are four catego­ries of lipids: droplets (isolated or in aggregates), fat oval bodies, lipid cylinders, and cholesterol crystals. The identi­cation of the rst three categories is facilitated using polar­ized light, which shows the typical “Maltese crosses”. These elements are associated with marked proteinuria.

The only automated analyzer of the corpuscular fraction of urine by cytouorimetry is the Sysmex UF analyzer, of which the model 1000i is the latest development. The Sysmex UF-1000i (Dasit) combines impedance technology with cyto­uorometry and uses a diode laser as the light source. The urine sample is aspirated and diluted with a buffer and then subjected to a staining process with two polymetin uoro­chromes, which can bind to nucleic acids. After a process of hydrodynamic focusing, the sample is passed through two ow cells, one dedicated to the analysis of microorganisms and the other dedicated to the analysis of all other corpuscular elements. The passage of the single particles is recognized by the impedance method, which allows their accurate quantica­tion and provides information about their size. In addition, the passage of particles suspended in the laminar ow deects the laser light beam and generates a diffraction signal which is read by both frontal (forward, 45°) and lateral (side, 90°) scat­ter detectors, as well as by a uorescence detector. The mea­sured parameters are converted into electrical signals that, analyzed through mathematical algorithms, allow the identi­cation of different elements present in the urine. The conduc­tivity of the solution is also measured and indicates the concentration of electrolytes in the urine. A new cytouori­metric system, UF-5000 Sysmex, which can be integrated with an image capture system, UD-10 Sysmex, is soon to be commercialized. The UF-5000 is the evolution of the UF-1000, while the UD-10 is a new system that, on the basis of grids selected by dedicated software, allows the evaluation of high­denition digital images to obtain a morphological picture to add to the cytouorimetric count, where necessary.

the traditional morphological examination in cases of a sim­ple denition, quantifying the corpusculate elements with precision and accuracy comparable to those of an experi­enced microscopist, using appropriate technology, method­ology and with reduced workload and allowing an effective selection of cases for which must be deepened by traditional microscopy or other analytical methods.