Chemical examination of urine
Apr 24, 2018
At present, chemical urine tests are carried out on automated analyzers using test strips that provide information on 8-12 parameters of urine.
pH.Normally, the pH of urine is usually weakly acidic, but may have a different reaction( 4.5-8).The main causes leading to a change in the pH of the urine are given in Table.
Table Diseases and conditions in which the pH of urine can vary
Table Diseases and conditions in which the pH of urine can vary
Protein. In healthy people, the protein in the urine is absent or its concentration is less than 0,002 g / l. The appearance of protein in the urine is called proteinuria. Methods for determining proteinuria by test strips and with sulfosalicylic acid give similar results, but they do not correlate well with the results of more accurate and complex analytical methods. Test strips are more sensitive to albumin, but do not catch the light chains Ig( Bens-Jones protein), so in patients with myeloma, this method can not be used. The method with sulfosalicylic acid determines all proteins, including paraproteins. In this regard, the detection of protein in the urine by the method with sulfosalicylic acid in combination with the negative result of the urine test strips with a high probability indicates the presence in the urine of light Ig chains. There are two main groups of proteinuria.
■ To the physiological proteinuria include cases of temporary appearance of protein in the urine, not related to disease. Such proteinuria is possible in healthy people after taking a large amount of food rich in proteins, after strong physical stress, emotional experiences, epileptic seizures. Functional is considered orthostatic, or juvenile, proteinuria, often observed in children and adolescents and passing with age. It should, however, be borne in mind that orthostatic albuminuria often occurs during recovery from acute glomerulonephritis. Functional proteinuria associated with hemodynamic stress is possible in children against a background of fever, emotional stress, congestive heart failure or hypertension, and also after cooling. This proteinuria is not related to the primary kidney damage and, by definition, disappears after eliminating the cause that caused it. It is generally believed that these types of transient proteinuria are benign and do not require in-depth examination. Nevertheless, with the help of modern research methods, some types of so-called physiological proteinuria managed to detect histological changes in the kidneys, which casts doubt on the functional nature of such disorders. A particularly serious prognosis is proteinuria, accompanied by hematuria and / or other symptoms of kidney damage.
■ Pathological proteinuria is divided into renal and extrarenal( prerenal and postrenal).
□ Extrinsic proteinuria is caused by an admixture of protein secreted by the urinary tract and genital organs;they are observed with cystitis, pyelitis, prostatitis, urethritis, vulvovaginitis. Such proteinuria rarely exceed 1 g / l( except in cases of pronounced pyuria).Detection in the urine of the cylinders indicates that the detected proteinuria, at least in part, has a renal origin.
□ In renal proteinuria, the protein enters the urine in the kidney parenchyma. Renal proteinuria in most cases is associated with increased permeability of the glomerulus. Renal proteinuria is most often associated with acute and chronic glomerulonephritis and pyelonephritis, nephropathy of pregnant women, feverish with
standing, severe chronic heart failure, amyloidosis of the kidneys, lipoid nephrosis, kidney tuberculosis, hemorrhagic fevers, hemorrhagic vasculitis, hypertensive disease.
False positive results with the use of test strips can be caused by pronounced hematuria, increased density( more than 1,025) and pH( above 8,0) urine, and by using aseptic to preserve it. The method with sulfosalicylic acid gives false-positive results when radiocontrast substances enter the urine, treatment with tolbutamide, penicillin, cephalosporins.
Glucose. Normally there is no glucose in the urine
Bilirubin. Normally, there is no bilirubin in the urine. Determination of bilirubin in urine is used as an express method for differential diagnosis of hemolytic jaundice and jaundice of another seizure( parenchymal and mechanical).Bilirubinuria is observed, mainly, in the defeat of the liver parenchyma( parenchymal jaundice) and violation of the outflow of bile( obstructive jaundice).For hemolytic jaundice, bilirubinuria is not characteristic, since indirect bilirubin does not pass through the renal filter.
Urolinogen. The upper limit of the reference value of urobilinogen in urine is 17 μmol / l( 10 mg / l).In clinical practice, the definition of urobilinuria is used:
■ to detect lesions of the liver parenchyma, especially in cases without jaundice;
■ for differential diagnosis of jaundice( with mechanical jaundice urobilinuria absent).
The causes of increased urobilinogen excretion in the urine are as follows.
■ Increased catabolism of Hb: hemolytic anemia, intravascular hemolysis( transfusion of incompatible blood, infection, sepsis), pernicious anemia, polycythemia, resorption of massive hematomas.
■ Increased urobilinogen formation in the gastrointestinal tract( GIT): enterocolitis, ileitis.
■ Increase the formation and reabsorption of urobilinogen in infections of the biliary system( cholangitis).
■ Violations of liver function: viral hepatitis( excluding severe forms), chronic hepatitis and cirrhosis of the liver, toxic liver damage( alcohol, organic compounds, toxins in infections and sepsis), secondary hepatic failure( after MI, cardiac and circulatory insufficiency, liver tumors).
■ Shunting of the liver: cirrhosis of the liver with portal hypertension, thrombosis, obstruction of the renal vein.
Ketone bodies. Normally, there are no ketone bodies in the urine. The most common cause of ketonuria is pronounced decompensation of type I diabetes mellitus, as well as long-term type II diabetes with depletion of P-cell pancreatic cells and development of absolute insulin-Isolation of urobilinogen and bilirubin with urine in viral hepatitis A
Fig. Isolation of urobilinogen and bilirubin with urine in viral hepatitis A
sufficiency. Expressed ketonuria is noted in hyperketonemic diabetic coma.
In patients with diabetes mellitus, monitoring of ketonuria is used to control the correctness of the selection of the food regime: if the amount of introduced fat does not correspond to the amount of digestible carbohydrates, then ketonuria increases. With a decrease in the introduction of carbohydrates( treatment without insulin) and the usual amount of fats, acetone begins to be released;in the treatment of insulin, a decrease in glucosuria is achieved by better assimilation of carbohydrates and is not accompanied by ketonuria.
In addition to diabetes mellitus, ketonuria can be detected with precomatous conditions, cerebral coma, prolonged starvation, severe fever, alcohol intoxication, hyperinsulinism, hypercatecholism, in the postoperative period.
Nitrite. Normally, nitrites are absent in the urine. Escherichia coli, Proteus, Klebsiella, Citrobacter, Salmonella, some enterococci, staphylococci and other pathogenic bacteria restore the nitrates present in urine to nitrites. Therefore, the detection of nitrite in the urine indicates the infection of the urinary tract. The test may be false-negative if the bacteria( Staphylococcus, Enterococcus and Pseudomonas spp.) Do not produce the enzyme nitrate reductase.
The incidence of infection by the results of a sample for nitrite is 3-8% among women, 0.5-2% among men. The high risk of asymptomatic infections of the urinary tract and chronic pyelonephritis occurs among the following population categories: girls and women, elderly people( over 70 years), patients with prostatic adenoma, diabetes, gout, urological operations or instrumental procedures on the urinary tract.
Leukocytes. Normally, in the urine, when tested with test strips, there are no leukocytes. The test for leukocyte esterase is positive if
the white blood cell count in urine exceeds 10-20 cells / μl. Leukocyturia is a sign of inflammation of the kidneys and / or the lower parts of the urinary tract. Leukocyturia is the most characteristic sign of acute and chronic pyelonephritis, cystitis, urethritis, stones in the ureter.
Erythrocytes. Physiological microhematuria when tested with test strips is up to 3 erythrocytes / μl of urine( 1-3 erythrocytes in the field of view with microscopy).Hematuria - the content of erythrocytes over 5 in 1 μl of urine - is considered a pathological sign. The main causes of hematuria are renal or urological diseases( urolithiasis, tumors, glomerulonephritis, pyelonephritis, urinary tract infections, kidney trauma, kidney damage in systemic diseases, etc.) and hemorrhagic diathesis. False positive results of urine testing for blood with test strips can occur with the use of beets, food dyes, large amounts of vitamin C, taking drugs( ibuprofen, sulfamethoxazole, nitrofurantoin, rifampicin, quinine, etc.), the presence of bile pigments, myoglobin,porphyrin-new, in case of blood during menstruation.
According to the "Recommendations of the European Association of Urologists for the treatment of urinary tract infections and reproductive system infections in men," the definition of leukocyturia( leukocyte esterase), erythrocyturia( Hb) and bacteriuria( nitrate reductase) using test strips is a diagnostic and therapeutic approach acceptable for clinical practiceacute cystitis and pyelonephritis.
Hb. When tested, test strips are not normally present. Hemoglobinuria and myoglobinuria can occur with severe hemolytic anemia, severe poisoning, sepsis, burns, myocardial infarction, muscle damage( prolonged crush syndrome), and severe physical exertion.