Diagnosis of urinary tract infections

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

• Symptoms of a urinary tract infection in young children are not specific, a urinary tract infection without fever can be missed or detected accidentally; In newborns, the infection of the urinary tract can be associated with bacteremia, meningitis.
• Ideally pure urine in newborns and young children can be obtained only by invasive methods: transurethral catheterization of the bladder or suprapubic urinary bladder puncture followed by aspiration of the urine sample.

Diagnostic value of symptoms and methods of examination

Fever

Numerous studies have shown that among the causes of acute fever in children from 3 years to 20% occupy pneumonia, bacteremia, meningitis and urinary tract infection. Particular attention should be paid to children with fever up to 39 ° C and above. R. Bachur and M.V. Harper (2001), examining 37 450 children of the first 2 years of life with fever, detected bacteriuria in 30% of patients, with a false-positive rate of 1: 250. Fever is a clinical sign of involvement of the kidney parenchyma, that is, the development of pyelonephritis.

It is necessary to assume the infection of the urinary tract in each child with an incomprehensible malaise and to examine urine in all children with fever.

Bacteriuria

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

It is proved that for isolation of bacteria urine should be collected by free urination into a clean container after a careful perineum toilet. The lack of culture growth from urine, obtained with free urination, unambiguously excludes the diagnosis of urinary tract infection. Ramage et al. (1999) showed that with a thorough cleansing of the baby's perineum, the sensitivity of the urine sample obtained with free urination reaches 88.9%, the specificity is 95%. The lack of the method of free urination is a high risk of contamination, especially in children of the first months of life. It is necessary to remember that typical contaminants are non-gold staphylococcus, green streptococcus, micrococci, corynebacteria and lactobacilli.

Diagnostic criteria for bacteriuria in pyelonephritis

Diagnostically significant should be considered bacteriuria:

• 100 000 or more microbial bodies / ml (colony forming units / ml) in urine collected in a sterile container with free urination;
• 10 000 or more microbial bodies / ml of urine collected by catheter; Heldrich F. Et al. (2001) consider not less than 1000 colony-forming units / ml of urine obtained by catheterization of the bladder to be diagnostic;
• any number of colonies in 1 ml of urine obtained from suprapubic urinary bladder puncture;
• for infants of the first year of life who did not receive antibiotics, a bacteriuria diagnostic is significant in the study of urine collected with free urination: 50,000 microbial bodies / ml of E. Coli urine 10,000 microbial bodies Proteus vulgaris, Pseudomonas aeruginosae.

Analysis of urine

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

The sensitivity and specificity of screening tests for infections of the urinary system (Stephen M. Downs, 1999)

Screen 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	+++	-

Microscopy of urine

Proper collection of urine and careful microscopy (counting of leukocytes) can have a sensitivity of up to 100% and specificity up to 97%. The indicators depend on the qualifications of the staff, the time of examination of the urine sample. It has been established that a three-hour delay in the study of urine after its collection reduces the quality of the results by more than 35%. If urine can not be examined within the next hour, urine samples should be stored in the refrigerator!

Most pediatricians-nephrologists believe that it is sufficient to conduct a general urinalysis to determine the leukocyturia with a count of the number of white blood cells in the field of vision.

Criteria of leukocyturia: in the general analysis of urine leukocytes no less than 5 in the field of view. In doubtful cases, it is advisable to study urine according to Nechiporenko (in norm the number of leukocytes is 2000 / ml of urine or 2x10 ⁶ / l of urine).

Instrumental diagnostic methods

Ultrasound examination of the organs of the urinary system

UGA is considered a non-invasive and safe method of instrumental examination in children with urinary tract infection. Conduction of ultrasound is possible at any time convenient for the patient and the doctor. The use of color and pulsed Doppler ultrasound has increased the diagnostic significance of the ultrasound investigation method, which allows to identify hydronephrosis, dilatation of pelvis and distal ureter, bladder hypertrophy, urolithiasis, signs of acute renal inflammation and shrinkage of the kidney.

Cystoureterography

Cystoureterography is indicated for all children under 2 years with a urinary tract infection. The need for such a rigid approach is due to the high incidence of vesicoureteral reflux (PMR), which is detected in 50% of children in the first year of life with a urinary tract infection. Children with a high degree of reflux (IV and V) are 4-6 times more likely to have a wrinkling of the kidney than children with a low degree of PMR (I, II, III) and 8-10 times more likely than children without PMR. The earlier the MTCT is identified, the greater the likelihood of a correct choice of treatment and prevention of recurrence of urinary tract infection. Optimal holding of cystography not only with tight filling of the bladder, but also during the exercise.

Scintigraphy (renoscintigraphy)

Static nephroscintigraphy with Technetium-99m-dimercaptosuccinic acid (DMSA) allows to detect the extent and extent of disorders in the renal parenchyma in pyelonephritis, the degree of shrinkage of the kidney. Currently, renoscintigraphy is considered the most accurate method of detecting the wrinkling of the kidney in children.

The frequency of changes in the parenchyma in DMSA in children with urinary tract infection and reflux

Research conditions	Results of the study with DMSA,%
	Normal	Questionable	Pathological
IMS (Ajdinovic B. Et al., 2006)	51	Eleven	38
IMS (Clarke SE et al., 1996)	50	13.7	36.5
IM without PMR (Ajdinovic B. Et al., 2006)	72	13	15
IMS + PMR (Ajdinovic B. Et al., 2006)	37	10	53

The sensitivity of renoscintigraphy reaches 84%, the specificity is 92%. Children under 4 years of age with a manifestation of urinary tract infection, fever and symptoms of intoxication (vomiting, decreased appetite, or anorexia) deserve special attention. Among patients with a wrinkling of the kidney, over 50% have multiple parenchyma lesions.

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

Excretory urography

For a long time, excretory (intravenous) urography was the only method for diagnosing anomalies in the genitourinary system. However, ultrasound revealed many anomalies more safely and less invasively. As a consequence, the indications for excretory urography are limited. Currently, excretory urography is used with yogexol or iodixanol, which do not have a negative effect on kidney function.

Cystoscopy

Cystoscopy refers to the methods of instrumental examination of children with urinary tract infection for the diagnosis of cystitis, urethritis, bladder anomalies and urethra.

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