Urinalysis is one of the most commonly performed laboratory tests. The following article presents the basic principles for performing and interpreting a urinalysis and urine culture. The most common symptoms of urinary tract diseases are also presented, highlighting the distinctions between different age groups.
Table of contents:
- Introduction
- Clinical manifestations of urinary tract diseases
- General urinalysis
- Interpretation of laboratory results
- Urine culture
- Interpretation of urine culture results
Introduction
Urinary tract diseases in children, especially in the youngest children, are sometimes difficult for parents to recognise, as they do not follow the same pattern as in adults. In the neonatal and early infant period, in addition to urinary tract infections, we still need to consider the presence of congenital abnormalities of the urinary tract. These congenital abnormalities may include:
- thefunction of the urinary tract, which is the excretion of unnecessary products of the "work" of the cells and tissues of the body, the maintenance of normal concentrations of sodium, potassium and other essential components, and the production of several hormones such as erythropoietin (responsible for the normal production of erythrocytes in the bone marrow), renin (allowing the maintenance of normal blood pressure) or vitamin D3 (necessary for the normal structure of the child's bones)
- theanatomy of the urinary system (malformation of the urethral orifice in boys, vesicoureteral reflux).
In an older child without a urinary tract defect, the most common disease is a urinary tract infection.
Clinical manifestations of urinary tract diseases
- In the newborn and infant, the parent or paediatrician usually finds:
- poorer weight gain,
- reluctance to eat,
- restlessness,
- prolonged jaundice,
- sub-fever or fever,
- gastrointestinal symptoms such as colic, urination, vomiting, abnormal stools.
Urinary tract diseases, photo: panthermedia
As can easily be seen, these symptoms can be present in a whole group of illnesses not related to the urinary tract or even be a phenomenon normally occurring in this period of the baby's life, for example, volvulence or colic. For this reason, the paediatrician, even in the case of symptoms apparently unrelated to the urinary tract, will order a general urine examination and culture to rule out urinary tract infection as the cause of these disorders.
- In children aged a few years or more, urinary tract infections may present as abdominal pain, flatulence, diarrhoea and, in chronic conditions, underweight, sub-febrile states or fever.
- Symptoms of lower abdominal pain and burning of the urethra typical of adults are reported by older children - usually over 6 years of age.
General urine examination
Is the easiest to perform and least invasive examination of the urinary system. In newborns and infants and young children who are not yet able to pee in the potty to collect urine, we stick a bag (different for boys, different for girls - available at the pharmacy without a prescription).
Before sticking the pouch on, it is necessary to wash the baby thoroughly with soap and water - for girls, wash from the pubic symphysis towards the anus so as not to contaminate the area around the urethral orifice with bacteria naturally found in faeces; for boys, gently remove the foreskin and wash the area around the urethral orifice.
It is best to stick the bag in the morning so that the so-called morning urine can be collected for examination, which allows a more precise assessment. When the child urinates, pour the urine into a plastic container and take it to the laboratory. If this cannot be done immediately, the container should be placed in the lower drawer of the refrigerator door to inhibit excessive bacterial growth, which could interfere with the test result. With an older child, the urine is collected for testing from the potty after washing it thoroughly.
However, it should be remembered that none of the above methods guarantees that the collection is completely sterile and clean. For this reason, the best material for testing is morning urine from the middle stream (the first portion of urine should be bypassed, then a cup should be substituted, filled with a small amount and moved away before the end of urination). This method of urine collection gives the most reliable result for a general examination and, for urine culture testing, is even the only recommended method for obtaining urine for testing.
Interpretation of laboratory results
- pH - this is the reaction of the urine; it can be acidic, neutral or alkaline. Normal urine is slightly acidic. Alkaline urine may indicate the presence of bacteria that alter the reaction.
- transparency of urine - freshly passed urine is transparent, slight turbidity may be related to the presence of excreted phosphorus ions, abnormally turbid urine occurs in urinary tract infections
- colouring of the urine - normally it is straw yellow, with drinking a lot of liquids the urine can be almost colourless, with dehydration even orange-brown. The colouring of the urine can change depending on the pigments ingested - for example, pink after eating beetroot. In small infants, the urine may stain the nappies red due to the presence of normal amorphous urate. In disease states, the following changes in urine colour can be observed: intensely orange in jaundice associated with the breakdown of erythrocytes and the release of pigment from them, red in urinary tract bleeding, the colour of meat washings in acute glomerulonephritis.
- urinedensity - in adults it ranges from 1016 to 1022. In newborns, whose urine thickening function is just developing, the density is 1005-1010. Older children have intermediate values. Urine density increases in states of dehydration and decreases with excessive fluid supply or diuretic administration.
- thepresence of protein in the urine - normally, protein is not present in the urinalysis. In some special cases such as exertion, prolonged standing, overheating, cold, stress, a slight proteinuria may occur, which is not a symptom of the disease. However, due to the association of proteinuria with abnormalities in the urinary system, whenever protein is found in the urine, the diagnosis should be expanded (repeat the general examination and, in addition, urine culture and evaluation of the so-called renal tests in the blood).
- thepresence of sugar in the urine - also similar to protein in a normal test result is not present. In children, sugaruria may occur during the administration of, for example, an intravenous infusion of a glucose drip, which is normal, or pathologically with high serum sugar concentrations in diabetes.
- thepresence of urobilinogen in the urine - it is normally present. Urobilinogen is a product of bilirubin metabolism, so its concentration increases - we then speak of increased urinary urobilinogen - in liver disorders (inflammation, cirrhosis) or with excessive release of bilirubin from damaged erythrocytes (haemolytic anaemias).
Urinary tract diseases in children, photo: panthermedia
- ketone compounds - commonly referred to as "acetone in the urine" - does not normally occur. Its presence is most frequently found in children during vomiting, especially when accompanied by fever (we then speak of acetonemic vomiting), in diabetes mellitus when too little insulin is administered at high blood sugar levels, during starvation or on a low-fat or low-sugar diet.
- urinesediment - epithelium lining the urinary tract, single leucocytes (up to 5-6 in boys and up to 10-12 in girls) and erythrocytes (up to 5 in the field of view), uric acid, urate and calcium oxalate crystals may be present.
- an increase in the number of leukocytes in the urine - so-called leukocyturia occurs most frequently in urinary tract infections
- an increase in the numberof erythrocytes in the urine - so-called erythrocyturia also occurs in urinary tract infections, in glomerulonephritis, after trauma, in urolithiasis, after excessive physical exertion, in blood diseases - haemorrhagic diathesis, or when urine was passed for examination during menstruation.
- presence of bacteria in the urine sed iment - this is most often from external contamination (in girls from vaginal secretions, in boys from under the foreskin). If bacteria are found in the sediment, a urine culture is necessary.
Urine culture
The procedure for taking urine for culture by the pouch method is identical to that for a general urine test with one difference. The container for the urine culture test is packaged sterile in a plastic bag (available from the pharmacy without a prescription). When collecting the urine for the test, remember not to touch the inside surface of the cap or the inside of the container with your finger, as bacteria on our skin can falsify the result of the child's test.
After pouring a small amount of urine from the bag, the container should be labelled and brought to the laboratory as soon as possible. If this is not possible, the material collected in this way should be stored in the doorway in a refrigerator. However, the longer the time between collection and culture, the more unreliable the result, due to the multiplication of bacteria already outside the child's body.
In an older child, midstream ur ine is the most suitable method for testing (method described above in the section on general urine testing). Midstream urine collection can be used even with the smallest children - babies often urinate spontaneously in certain situations, e.g. in the morning after undressing.
Urine examination, photo: panthermedia
Interpretation of urine culture results
- if bacteria are visible in the mid-stream sediment and the bacteriological result is negative, this suggests that the bacteria in the sediment were not alive
- the number of bacteria in the urine of healthy people, usually due to external contamination, should not exceed 10,000 (104) - 100,000 (105) per ml
- a bacterial count of 10,000 bacteria per ml in boys and 100,000 and above in girls, or 10,000 bacteria per ml in girls, but with accompanying clinical symptoms, suggests a urinary tract infection - this is known as significant bacteriuria
- the finding of Pseudomonas aeruginosa in a urine culture, regardless of the amount of bacteria, requires treatment.
If it is difficult to obtain a reliable test result when a urinary tract infection is suspected in a hospital setting, urine can be collected for examination by suprapubic puncture. This is performed with a needle through the abdominal layers. Urine collected in this way is interpreted as follows: any number of Gram-negative bacteria and more than 1000 Gram-positive bacteria per millilitre require treatment.
Another method is bladder catheterisation, but this method is not often used due to the possibility of introducing bacteria via the ascending bladder route. If there are more than 10 000 bacteria per ml in the urine collected by this method, this suggests a urinary tract infection and requires treatment.