Diagnosis of urinary tract infections

When examining children with suspected urinary tract infection, preference is given to minimally invasive methods with high sensitivity. The difficulty of diagnosing urinary tract infection is primarily noted in young children (newborns and the first 2 years of life) and there are several reasons for this.

• Signs of urinary tract infection in young children are nonspecific, urinary tract infection without fever may be missed or detected incidentally; in newborns, urinary tract infection may be associated with bacteremia, meningitis.
• Perfectly clean urine in newborns and young children can only be obtained by invasive methods: transurethral catheterization of the bladder or suprapubic puncture of the bladder followed by aspiration of a urine sample.

Diagnostic value of symptoms and examination methods

Fever

Numerous studies have shown that pneumonia, bacteremia, meningitis and urinary tract infection account for up to 20% of the causes of acute fever in children aged 3 years. Particular attention should be paid to children with fever up to 39 °C and above. R. Bachur and M.B. Harper (2001), examining 37,450 children of the first 2 years of life with fever, found bacteriuria in 30% of patients, while the frequency of false-positive results did not exceed 1:250. Fever is a clinical sign of involvement of the renal parenchyma, i.e. the development of pyelonephritis.

A urinary tract infection should be considered in any child with unexplained illness and the urine should be examined in all children with fever.

Bacteriuria

The diagnosis of urinary tract infection should be based on the isolation of a culture from specially collected urine. The ideal method is aspiration puncture of the bladder. Detection of bacterial growth from urine obtained by puncture confirms urinary tract infection in 100% of cases (this method has 100% sensitivity and specificity). However, aspiration puncture requires well-trained personnel, is quite unpleasant for the child and cannot be used repeatedly.

It has been proven that in order to isolate bacteria, urine should be collected by free urination in a clean container after thorough perineal hygiene. The absence of culture growth from urine obtained by free urination clearly excludes the diagnosis of urinary tract infection. Ramage et al. (1999) showed that with thorough cleaning of the child's perineum, the sensitivity of the study of urine samples obtained by free urination reaches 88.9%, specificity - 95%. The disadvantage of the free urination method is the high risk of contamination, especially in children in the first months of life. It is necessary to remember that typical contaminants are non-golden staphylococcus, viridans streptococcus, micrococci, corynebacteria and lactobacilli.

Diagnostic criteria for bacteriuria in pyelonephritis

Bacteriuria should be considered diagnostically significant:

• 100,000 or more microbial bodies/ml (colony forming units/ml) in urine collected in a sterile container during free urination;
• 10,000 or more microbial bodies/ml of urine collected using a catheter; Heldrich F. et al. (2001) consider at least 1000 colony-forming units/ml of urine obtained by catheterization of the bladder to be diagnostically significant;
• any number of colonies in 1 ml of urine obtained by suprapubic puncture of the bladder;
• For children in the first year of life who have not received antibiotics, when examining urine collected during free urination, bacteriuria is diagnostically significant: 50,000 microbial bodies/ml of urine E. coli 10,000 microbial bodies Proteus vulgaris, Pseudomonas aeruginosae.

Urine analysis

Diagnosis of bacterial inflammation in the genitourinary system in children can be carried out using screening tests (test strips) that determine leukocyte esterase and nitrite in urine. The absence of esterase and nitrite simultaneously allows us to exclude a bacterial infection of the genitourinary system.

Sensitivity and specificity of screening tests for urinary tract infections (Stephen M. Downs, 1999)

Screening test	Sensitivity	Specificity
Leukocyte esterase	+++ (up to 94%)	++ (63-92%)
Nitrite	+ (16-82%)	+++ (90-100%)
Definition of bacteriuria (dipslide)	++ (up to 87%)	+++ (up to 98%)
Proteinuria	+++	-
Hematuria	+++	-

Urine microscopy

Correct urine collection and careful microscopy (white blood cell count) can have a sensitivity of up to 100% and a specificity of up to 97%. The indicators depend on the qualifications of the personnel, the time of urine sample analysis. It has been established that a three-hour delay in urine analysis after its collection reduces the quality of the results by more than 35%. If it is impossible to analyze urine within the next hour, urine samples should be stored in the refrigerator!

Most pediatric nephrologists believe that a general urine test with a leukocyte count in the field of view is sufficient to detect leukocyturia.

Leukocyturia criteria: in a general urine analysis, there are at least 5 leukocytes in the field of vision. In doubtful cases, it is advisable to conduct a urine test according to Nechiporenko (normally, the number of leukocytes is 2000/ml of urine or 2x10 ⁶ /l of urine).

Instrumental diagnostic methods

Ultrasound examination of the urinary system

UZA is considered a non-invasive and safe method of instrumental examination in children with urinary tract infection. Ultrasound can be performed at any time convenient for the patient and the doctor. The use of color and pulsed Dopplerography has expanded the diagnostic significance of the ultrasound method of examination, which allows identifying hydronephrosis, dilation of the renal pelvis and distal ureters, hypertrophy of the bladder walls, urolithiasis, signs of acute renal inflammation and renal shrinkage.

Cystoureterography

Cystourethrography is indicated for all children under 2 years of age with urinary tract infection. The need for such a strict approach is due to the high incidence of vesicoureteral reflux (VUR), which is detected in 50% of children in the first year of life with urinary tract infection. Children with a high degree of reflux (IV and V) are 4-6 times more likely to have renal scarring than children with a low degree of VUR (I, II, III), and 8-10 times more likely than children without VUR. The earlier VUR is detected, the greater the likelihood of the correct choice of treatment and prevention of recurrent urinary tract infection. Cystography is optimally performed not only with tight filling of the bladder, but also during urination.

Scintigraphy (renoscintigraphy)

Static renal scintigraphy with Technetium-99m-dimercaptosuccinic acid (DMSA) allows to detect the degree and prevalence of disturbances in the renal parenchyma in pyelonephritis, the degree of renal scarring. Currently, renal scintigraphy is considered the most accurate method for detecting renal scarring in children.

Frequency of parenchymal changes in DMSA in children with urinary tract infection and reflux

Conditions of the study	Results of the study with DMSA, %
	Normal	Doubtful	Pathological
IMS (Ajdinovic B. et al., 2006)	51	11	38
IC (Clarke SE et al., 1996)	50	13.7	36.5
IMS without PMR (Ajdinovic B. et al., 2006)	72	13	15
IMS+PMR (Ajdinovic B. et al., 2006)	37	10	53

The sensitivity of renal scintigraphy reaches 84%, specificity - 92%. Particular attention should be paid to children under 4 years of age with manifest urinary tract infection, fever and symptoms of intoxication (vomiting, loss of appetite or anorexia). Among patients with renal shrinkage, over 50% have multiple areas of parenchymal damage.

Static renoscintigraphy is limited to determining parenchymal defects. Dynamic renoscintigraphy with technetium makes it possible to determine the nature of renal hemodynamics, disorders of the secretory and excretory functions of the kidneys, and to exclude obstruction of the urinary tract.

Excretory urography

For a long time, excretory (intravenous) urography was the only method for diagnosing urogenital anomalies. However, ultrasound has made it possible to detect many anomalies more safely and less invasively. As a result, the indications for excretory urography are limited. Currently, iogexol or iodixanol are used for excretory urography, which do not have a negative effect on kidney function.

Cystoscopy

Cystoscopy is considered a method of instrumental examination of children with urinary tract infection for the diagnosis of cystitis, urethritis, and abnormalities of the bladder and urethra.

[ 1 ], [ 2 ], [ 3 ], [ 4 ], [ 5 ], [ 6 ], [ 7 ], [ 8 ], [ 9 ], [ 10 ]