Urine is the result of the body’s metabolism and is excreted through the urinary system and urinary tract. The production of urine depends on the filtration of the glomerulus and the reabsorption and secretion of the renal tubules and collecting ducts. Urine abnormalities can indicate the health status of the body. As one of the three routine tests, urine routine is an adjunctive test for many diseases.
General urine tests include urine color, clarity, specific gravity, urine pH, urine leukocytes, nitrites, protein, glucose, urine ketone bodies, urine bilirubin, urine red blood cells, etc.
Color
The color of urine in normal people is pale yellow and can also change slightly with changes in water intake, activity, and diet. Common abnormal urine colors include the following.
Dark tea-colored urine: bilirubin positive, mostly seen in hepatocellular jaundice, obstructive jaundice, etc.
Red urine: hematuria, which can be seen in urinary stones, tumors, infections (including tuberculosis), glomerulonephritis, etc.
Of course, some drugs can also cause red urine, such as aminopyrine, phenytoin sodium, rifampin, etc. Therefore, when hematuria is found, we must first exclude the influence of these “destructive molecules” and combine them with the patient’s clinical symptoms to find the cause one by one.
Beer-like to soy sauce-colored urine: hemoglobinuria, seen in serum disease, etc.
Milky white urine, celiac disease, pus urine: common in filariasis, or urine containing large amounts of inorganic salt crystals.
Transparency
Normal fresh urine is mostly clear and transparent, except for urine that has been left for a long time and urine contaminated by female secretions which can be slightly cloudy. Cloudy urine is mostly seen in urate crystals, celiac disease, pus urine, and hematuria.
pH value
The normal range is 4.6-8.0. The pH of urine depends largely on the type of diet, medications taken and the type of disease.
Low values are seen in diabetic ketoacidosis, starvation, severe diarrhea, whistling acidosis, fever, etc.
High is seen in severe vomiting, persistent hyperventilation, urinary tract infections, etc.
Specific Gravity
The normal range is 1.005-1.030. The specific gravity of urine is influenced by age, water intake and sweating, and is low in infants and children. The specific gravity of urine depends mainly on the concentration function of the kidney, so it can be used as one of the kidney function tests.
Increased specific gravity: seen in acute nephritis, hyperthermia, cardiac insufficiency when urine is low; seen in diabetes when urine is increased.
Decrease in specific gravity: seen in chronic glomerulonephritis, renal insufficiency, uremia, and heavy water consumption.
Leukocytes
Normal urine microscopy will not have more than 5 white blood cells, if a large number appear then the possibility of urinary tract infection should be considered. However, it should be noted that there are many factors that affect urine leukocytes: crystals, small round epithelial cells, yeast, trichomonas and other components can lead to an increase in leukocytes and cause false positives. And jaundiced urine and urine left for too long can lead to lower leukocytes, resulting in false negatives. Therefore, urinary tract infections cannot be judged solely from positive urine leukocytes, but need to be combined with the nitrite results described below.
Nitrite
Under normal circumstances, urine is negative for nitrite. Positive urine nitrite results are commonly seen in: pyelonephritis caused by Escherichia coli (about two-thirds of cases), as well as urinary tract infections, cystitis, and bacteriuria.
The specificity of urinary nitrite can reach 80%, and it has a high value to assist in the diagnosis of urinary tract infections, and a positive nitrite can basically be a preliminary judgment of urinary tract infections. If the urinary tract infection bacteria (such as positive bacteria) cannot reduce nitrate to nitrite, or if the urine remains in the bladder for a short period of time, or if there is a lack of nitrate in the urine, it will also produce a negative result and needs to be noted.
Erythrocytes
Normal urine will occasionally show red blood cells, but no more than 3. If more red blood cells appear, they may be excreted from the kidneys or urinary tract bleeding, and should also be considered to be caused by impaired blood circulation. Sometimes there may be positive urine occult blood and negative urine red blood cells. This is due to the fact that the red blood cells in the urine are affected by the osmotic pressure in the urine and other factors and finally break down. It is not possible to tell where the lesion is occurring simply from hematuria or urine red blood cells. If a patient develops hematuria, urine red blood cell morphology testing is of great significance in determining the source of the hematuria. At the same time, the combination of the patient’s clinical manifestations, urine protein condition and imaging findings can help comprehensive analysis and judgment.
Urine protein
Normal people occasionally have small amounts of protein in their urine, including albumin, globulin and some other small molecular weight proteins secreted by the renal tubules. A normal routine urine examination is negative for urine protein, and the total amount of protein in the urine in 24 hours is less than 150 mg, of which albumin does not exceed 30 mg. There are many causes of proteinuria, and to diagnose pathological proteinuria, the following factors need to be excluded.
Functional proteinuria: mental stress of the body, strenuous exercise, low temperature stimulation, mostly seen in adolescents.
Postural proteinuria: negative when lying down, positive when standing for too long, mostly seen in adolescents.
Incidental proteinuria: False positive for urine protein can occur when genital excretion is mixed in the urine. The opposite is true when the patient has had a large injection of penicillin, which can lead to a false negative for urine protein. Urine protein test is also an important indication for patients with kidney disease. If a patient is determined to have clinical diagnostic value with positive urine protein, further 24-hour urine protein quantification may be done.
Urine ketone body
A normal person has a negative urine ketone body qualitative test. In starvation, impaired glucose metabolism due to various reasons, increased lipolysis and diabetic ketoacidosis, ketonemia can occur due to the rate of ketone body production being greater than the rate of tissue utilization, followed by ketonuria. Positive urinary ketone bodies are often associated with diabetes, pregnancy, malnutrition, and chronic diseases, such as diabetic ketoacidosis. It may also result from severe diarrhea, vomiting, starvation, chloroform, after ether anesthesia, phosphorus poisoning; taking biguanide hypoglycemic agents, etc.
Urine bilirubin, etc.
Urinary bilirubin, urobilinogen, and urobilin are mainly used as the differential diagnosis of jaundice, and their results need to be integrated together to guide clinical diagnosis and treatment. This item, together with urobilinogen and urobilin, is used as a differential diagnosis for jaundice.
Tubular urine
There is no tubular pattern in normal urine, or a few clear tubular patterns are occasionally seen. The presence of tubular patterns in urine, especially granular and cellular tubular patterns, is a sign of substantial renal lesions and is important for diagnosis.
Clear tubular pattern: seen in the urine when the kidney has mild or temporary functional changes, such as strenuous exercise, high fever and cardiac insufficiency, a small amount of clear tubular pattern can be seen; when the kidney has substantial lesions, a large amount of clear tubular pattern can be seen.
Erythrocyte tubular pattern: seen in acute glomerulonephritis, acute tubular necrosis, renal hemorrhage and acute rejection of renal transplantation.
Leukocytic tubular pattern: seen in purulent inflammation of the kidney, such as acute pyelonephritis, interstitial nephritis, etc.
Granular tubular pattern: seen in organic lesions of the kidney, such as chronic nephritis, drug poisoning-induced tubular injury.
Waxy tubular type: seen in severe glomerulonephritis, advanced chronic nephritis, its appearance suggests long-term and serious lesions in the kidney.
Fatty tubular pattern: the product of fatty degeneration of renal epithelial cells, seen in chronic nephritis and lipid-like nephropathy, etc.
To sum up, urine routine is such a simple and easy test, but it provides so much information that it is worth learning to make good use of.