Sometimes, the study of urine includes knowing its microscopic characteristics (employing the urine sediment to see the presence of cells, crystals, cylinders and bacteria) and its culture (urine culture to identify germs).
Characteristics of urine
Under normal conditions, urine is light yellow and depending on its concentration (water content), it can take on a light yellow colour (if it is diluted) or dark yellow (if it is concentrated). Normal urine does not usually contain chemicals or abnormal elements (cells, crystals) or only traces. Thus, urine may have a cloudy appearance if there are cells (leukocytes, red blood cells) or crystals. Alternatively, also if certain medications are being taken since the urine could be stained by them.
Various chemical parameters are included in the dipstick urinalysis. Two of them are esterase (or leukocyte esterase) and nitrites. Esterase is a protein found in white blood cells or leukocytes, and if these are in the urine, we can detect the presence of esterase with the test strip. The presence of nitrites indicates the presence of bacteria in the urine and, consequently, a probable urinary tract infection. Introducing a reactive strip in the urine sample causes it to change to a violet colour in the presence of esterase and nitrites, putting us on the trail of a urinary infection.
The presence of nitrites and esterase in the test strip will indicate the need to study the urinary sediment and, sometimes, a urine culture. The urinary sediment is investigated for the presence of cells (including white blood cells and red blood cells), crystals, casts, and bacteria. The crystals are due to the crystallization of some substances dissolved in the urine, mainly salts. Casts are like imprints of the renal tubules created when urinary cells, proteins, or both precipitate in the renal tubules and are eliminated in the urine. The presence of crystals and cylinders can guide us to kidney or urinary tract diseases.
It consists of incubating the urine in specific bacterial growth media to identify the possible cause of the infection.
Urine culture (uroculture)
The results of all these studies (dipstick, sediment and urine culture) are usually ready in a few minutes (the dipstick) or a few hours (the sediment) or a few days (the urine culture). However, some types of bacteria reproduce slowly, which may take several days or weeks.
How should urine collection be?
It is essential to obtain a urine sample in the best possible conditions. Depending on the study we will carry out, we will need one type of urine sample or another. In the case at hand, and for a simple test strip, it could be a random sample, a urine sample taken randomly at any time. However, collecting the urine several hours after the last urination would be preferable. In the case of taking a sample to make sediment and culture, it is preferable to take extreme measures to collect urine.
Before collecting the urine, it is essential to wash the external genitalia with warm soapy water and then rinse with plenty of water and dry well. The urine must be collected in a clean or sterile container (usually, this container is wrapped in a small plastic bag that maintains cleanliness) and with an airtight seal. The container should not be uncovered until it is ready and urine collection is to begin. It is better to ignore the first stream and collect the middle portion of the urine stream "on the fly" without stopping urination. If there will be some time between collection and delivery to the laboratory, it is best to keep it in a cool place (for example, the refrigerator); you do not have to freeze it. Then it will have to be transported to the laboratory, trying to alter it as little as possible (basically that the container is in a vertical position, well covered and without being subjected to high temperatures), and quickly bring the sample to the laboratory. It is also essential that the container where the urine sample is collected is well labelled with our name and some other information that allows correct identification.
hand with a blue glove holding a urine tube and urine bottle next to it
What do we mean by leukocytes in urine?
The presence in the urine sediment of an excessive number of erythrocytes (or erythrocytes or red blood cells) is called “hematuria.” Moreover, an excessive number of leukocytes (or white blood cells) is called “leukocyturia.”
Yes, in the urine. In addition to leukocytes, erythrocytes are detected, and both are in the same or similar proportion as in the blood; we cannot speak of leukocyturia but simple hematuria.
What number of leukocytes is average?
A few white blood cells (up to 5 leukocytes per high-resolution field, 400x field) may be expected when the urine is examined under a light microscope. We speak of leukocyturia when the values are equal to or greater than five leukocytes.
The laboratory result can also be expressed in other units: thus, the presence of up to 10 leukocytes per microliter (mcL) or 10,000 cells per millilitre (mL) is considered normal.
Significance of the presence of leukocytes
The presence of high leukocytes in the urine does not mean, from the outset, that we should be alarmed. Moreover, most cases, the cause will be a minor health problem. The urinalysis results must always be correlated with the person’s health status (current symptoms, previous history of any disease, taking medication for another reason, etc.).
Why can leukocytes appear?
The possible causes of the presence of leukocytes in the urine are many, but from the outset, you should always think of a urine infection as the first option.
It is the most common cause, especially in women. It can correspond to cystitis (the usual) or pyelonephritis and is caused by bacteria. Symptoms of cystitis include burning or itching when urinating, painful urination, frequent urination, cloudy colour and harmful smell of urine, and sometimes weakness, tiredness, and fever.
The symptoms are of sudden appearance and with variable intensity. Pyelonephritis (kidney infection) is a more severe infection and manifests with pain and frequent urination accompanied by high fever, chills, rapid heartbeat, and vomiting. There is a higher chance of developing a kidney infection if a person is immunosuppressed (weak immune system) or has been using a urinary catheter for some time. In the urine analysis, we will find the presence of bacteria and nitrites in addition to numerous leukocytes.
Urine infection without bacteria:
It is possible to have leukocytes in the urine and with symptoms of bacterial infection, but without evidence of such an infection (there are no bacteria in the sediment or the culture). It is called sterile leukocyturia. This occurs in a urinary tract infection that has been “decapitated” by antibiotic treatment or not finished or with partial resistance of the germ to the antibiotic used. Some sexually transmitted diseases, viral or fungal infections or even tuberculosis can cause this. In these cases (except in the case of viruses, which we can study better in blood tests), a unique culture must be done to demonstrate these germs.
Bacteria in urine without symptoms:
It is the presence of bacteria in the urinalysis (confirmed in the sediment and the urine culture) but without symptoms. It is called asymptomatic bacteriuria. Since there are no symptoms, the urinalysis may have been done for another reason. This entity is not usually treated with antibiotics; this treatment is only reserved when the person has an increased risk if a urinary tract infection is produced by not treating it.
Acute and chronic prostatitis:
This entity only occurs in men. The acute form is characterized by pain when urinating, difficulty urinating, frequent urination, especially at night, fever and chills. There may also be a pain in the abdomen, pelvis, or lower back. Chronic prostatitis is rare and usually occurs with repeated episodes as if it were an acute infection (increased frequency, urgency and burning when urinating). Between episodes, there may be no symptoms, or you may present a sustained clinic of pain in the lower abdomen or pelvis.
Lithiasis (stones) or grit in the kidney or urinary tract:
Typical symptoms are lower back pain, difficulty urinating, decreased amount of urine, nausea, vomiting, chills, and fever. We find leukocytes, erythrocytes and crystals in the urinalysis, but there should be no bacteria.