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The kidneys’ main function is to eliminate metabolic waste products and to maintain balance of sodium,potassium, chloride, water and many other vital elements in the body. Blood flows into the kidneys where over one million small “filters” serve to remove these waste products and form urine. The kidneys are also important in the maintenance of blood pressure and in the production of a hormone that stimulates production of red blood cells. About half the time, doctors can fix the problems that cause kidney failure in a few days or weeks. These people’s kidneys will work well enough for them to live normal lives.But other people may have permanent kidney damage that leads to chronic kidney disease.
Renal failure or kidney failure is a situation in which the kidneys fail to function adequately. It is divided in acute and chronic forms; either form may be due to a large number of other medical problems. Biochemically, it is typically detected by an elevated serum creatinine. In the science of physiology, renal failure is described as a decrease in the glomerular filtration rate.
Urea Nitrogen is a waste product derived from the natural breakdown of protein in the liver. Urea is excreted in the urine after blood is filtered through the kidneys. The urea nitrogen level reflects both the metabolism of protein and the effectiveness of the kidneys in filtering blood.
Sodium, Chloride and Potassium, collectively known as electrolytes, are important for salt and water balance. Imbalances may be due to problems with diet, fluid intake, medication, kidney disease, or lung disorders. These tests are interpreted together. A high sodium or chloride level may be caused by an excessive intake of salt or by not drinking enough water.
Potassium measurements are useful in monitoring electrolyte balance in the diagnosis and treatment of disease conditions characterized by low or high potassium levels.
Sodium, Chloride and Potassium, collectively known as electrolytes, are important for salt and water balance. Imbalances may be due to problems with diet, fluid intake, medication, kidney disease, or lung disorders. These tests are interpreted together.
Creatinine is the most common test to assess kidney function. Creatinine levels are converted to reflect kidney function by factoring in age and gender to produce the eGFR (estimated Glomerular Filtration Rate). As the kidney function diminishes, the creatinine level increases; the eGFR will decrease.
Chronic kidney disease may be present in 10% of the adult population, most often secondary to high blood pressure or diabetes. Chronic kidney disease is defined by the presence of glomerular filtration rate (GFR) <60 mL/min/1.73m2 for a minimum of three months and/or evidence of kidney damage (e.g., structural abnormalities visualized on biopsy, imaging studies, and proteinuria) for at least three months. Thus, detection and monitoring of chronic kidney disease should include the calculated eGFR based on the creatinine test, age, and gender. Other important tests of kidney function include microalbuminuria and the urinalysis, especially looking for the presence of red and white blood cells in the urine.
The BUN/creatinine ratio is a calculated value derived by dividing the urea nitrogen result by the creatinine result. This ratio can be helpful in determining whether an elevated urea nitrogen is due to impaired kidney function or to other factors such as dehydration, urinary blockage, or excessive blood loss.
Anions are negatively charged molecules (such as Carbon Dioxide) and cations are positively charged molecules (such as Sodium and Potassium). These are always in balance. The anion gap is a calculation that reflect the balance or “gap” between the measured anions and cations.
Colour of urine is a basic and potentially informative test. Normal colour is light yellow due to natural pigments. Certain foods, medications, and vitamins may affect the colour. Medications that affect urine’s colour include chloroquine, iron supplements, and riboflavin. Blood should not be found in the urine. It will change the colour to pink to red. Infections and diseases of the liver and other systems will alter the colour as well.
Turbidity or cloudiness of urine may be caused by excessive cellular material or protein in the urine or may develop from crystallization or precipitation of salts upon standing at room temperature or in the refrigerator.
pH is a measure of how acid (acidity) or basic is the urine reflecting the acid-base balance in the body. The pH may be evidence of a certain type of bacteria known as ureasplitting bacteria that may infect the urinary tract. Also, pH is useful in the identification of crystals that may be found in the urine.
Specific gravity measures urine density, or the ability of the kidney to concentrate or dilute the urine over that of plasma (the liquid part of blood). Specific gravity serves to rate how well the kidneys can concentrate the urine. Measurements below the reference range indicate hydration and any measurement above it indicates relative dehydration. A high specific gravity may be due to dehydration. Alternatively, a urine specimen with a high specific gravity is either contaminated, contains very high levels of glucose, or the individual may have recently received high-density radiopaque dyes intravenously for radiographic studies.
Typically, only a small amount of glucose (a sugar) is found in the urine. In people with diabetes, the blood level of glucose is high and some of the excess is found in the urine. In addition to being evidence of uncontrolled diabetes, urinary glucose may be due to certain drugs that impair kidney function or to a congenital abnormality.
Bilirubin is produced by the liver and concentrated in the gallbladder. An increased level of urinary bilirubin suggests an abnormality in the function of liver (including hepatitis and cirrhosis – scarring of the liver) or gallbladder (including gallstones).
Ketones (acetone, acetacetic acid, beta-hydroxybutyric acid) resulting from either diabetic ketosis or some other form of calorie deprivation (starvation), are easily detected using either dipsticks or test tablets containing sodium nitroprusside. People who adopt the Dr. Atkins diet may have transient urinary ketones present.
Blood in the urine may be due to diseases along the urinary tract (kidneys, bladder, or urethra. Occasionally, excess bleeding or inflammation associated with appendicitis, diverticulitis, or an abdominal tumor may lead to blood in the urine. The test for blood is based on detection of hemoglobin, the predominant protein in red blood cells. This test is often more sensitive than detection of intact red blood cells because red blood cells can burst and be difficult to detect on a urinalysis examination.
The protein test is one of the most important tests in the urinalysis. A slight excess of protein may be due to strenuous exercise. Excess protein may suggest diseases of the kidneys.
A positive nitrite test indicates that bacteria may be present in significant numbers in urine. Certain types of bacteria that are common causes or urinary tract infection, such as E. coli, are more likely to give a positive test than other causes of infection. When nitrites, leukocyte esterase, and WBCs are detected, the likelihood of a urinary tract infection is high.
A positive leukocyte esterase test results from the presence of white blood cells either as whole cells or as broken cells.
The presence of more than five white blood cells (WBCs) in a microscopic field in urine is often evidence of a urinary tract infection. The higher the white blood cell count, the more likely an acute infection is present. A urinary tract infection is best diagnosed by performing a urine culture.
Red blood cells should not be found in the urine. Their presence may indicate trauma to the kidneys, disease of the kidneys, kidney stones, tumor in the bladder, or infection of the prostate (men only).
Squamous epithelial cells are found in the end of the urethra (closest to the skin) and vagina and vulva (in women). The presence of squamous epithelial cells is not unusual and has little clinical meaning by itself.
Transitional epithelial cells line much of the urinary tract including the bladder, ureters (the tubes that connect the kidneys to the bladder), and the urethra. Occasional transitional epithelial cells can be found in urine. When the number is high, there may be something irritating the cell lining such as kidney stones, trauma, inflammation, or tumor.
Renal tubular epithelial cells normally slough into the urine in small numbers. However, with certain kidney conditions that lead to kidney tubular degeneration, the number of renal tubular epithelial cells sloughed is increased.
Bacteria in the urine can be a contaminant from improper specimen collection or evidence of a urinary tract infection. Infection is supported by finding white blood cells and is best confirmed by a urine culture in which bacteria are identified and antibiotics are tested to find one that are effective in treating the bacterial infection.
Calcium oxalate crystals are often found because of diets with certain foods including spinach, tomatoes, rhubarb, garlic, oranges, asparagus, and tea. High does of vitamin C can induce calcium oxalate crystal formation. These crystals can also be found in people with high levels of calcium and increased activity of the parathyroid glands.
Triple-phosphate crystals typically have no clinical significance. They can form when there are bacteria that produce ammonium carbonate.
Uric acid crystals typically have no clinical significance. They are most likely to be identified when there is excessive uric acid as may be present with gout or high cell turnover, as with psoriasis (a skin condition) or following cancer treatments.
Amorphic cells have no particular shape and lack definite form and hence also called amorphous. Along with cell edema (cell swelling), appearance of amorphous dense deposits in the mitochondria of the cells indicate the ultrastructural change that are organ specific in response to disease.
Many different types of crystals may be found in the urine. For example, tyrosine and leucine crystals may be observed in people with severe liver disease and some genetic disorders. Other crystals are associated with formation risk or presence of kidney stones. Many crystals have no clinical significance.
The kidneys are formed by two million units called nephrons that filter the blood and lead to the formation of urine. Urinary casts are formed in the distal portion of the nephrons. Factors contributing to cast formation include low flow rates, high salt concentration, and low pH. Hyaline casts can be seen in people who exercise vigorously or who are on high carbohydrate diets. If persistent, hyaline casts suggest injury to the kidneys including kidney disease.
Granular casts are consistent with kidney disease.
Although hyaline casts can sometimes be observed in healthy people (in selected circumstances), most casts suggest injury to the kidneys including kidney disease.
Yeasts may infect the urinary tract or may be present as a contaminant from the skin. A yeast infection is usually accompanied by an increase in WBCs.
Microalbumin is a bit of a misnomer. The test detects albumin, the most abundant protein in the blood, in urine specimens. Normally no or only small amounts of albumin are found in the urine. But with early impairment of kidney function, the microalbulim level increases. For many individuals, an elevated microalbumin level, confirmed on repeat testing, is the first evidence of kidney damage. The test is especially recommended annually for individuals with diabetes and/or high blood pressure and for those with a family history of chronic kidney disease. When detected early, kidney disease may be treated and the progression to kidney failure slowed or halted.
Measurement of creatinine levels in urine is useful in the management of patients suffering from diabetes mellitus to assist in avoiding or delaying the onset of diabetic renal disease.
The Microalbumin/creatinine ratio is a calculated value derived by dividing the microalbumin result by the creatinine result. This ratio can be helpful in determining whether an elevated microalbumin is due to impaired kidney function or to other factors such as dehydration, urinary blockage, or excessive blood loss.