Examination of a urine specimen (urinalysis) is the easiest way to determine whether the kidneys are inflamed or damaged. When damaged, the kidneys can leak red or white blood cells or protein. A typical urinalysis report will describe the specific gravity, which reflects how well the kidney is concentrating the urine. This must be evaluated with reference to whether someone has been drinking a lot or is dehydrated. If a person is dehydrated, the urine should be concentrated and have a high specific gravity. If he or she has too much fluid in the body, the urine should be dilute.
Sugar in the urine is called glycosuria. Normal people do not lose any sugar in the urine, but diabetics do. Children being treated with high doses of corti-costeroids sometimes begin to lose sugar in their urine. If they do, it is an indication that they are moving toward diabetes and efforts should be made to reduce the corticosteroids. Another substance that may be found in the urine is ketones. Normally, there are no ketones in the urine. They are an indication that the body is metabolizing fat instead of carbohydrates. In someone who is sick or has not eaten well for a significant period, this is a normal finding. However, in a diabetic it may be a sign of significant trouble. Anyone with both ketones and glucose needs to be evaluated by a physician immediately.
Protein in the urine needs to be monitored carefully. Some people have orthostatic proteinuria, which means that their kidneys leak protein when they are standing for a prolonged period. This is a common and unimportant condition. This can be determined by checking a morning specimen. After lying down all night, they should not have protein in their urine. Other people have protein in their urine after a lot of physical activity, especially running. This is not significant either. However, people with nephrotic syndrome, a type of kidney damage, may constantly lose a lot of protein. This is determined by measuring the excretion of protein over a twenty-four-hour period or by comparing the ratio of protein to creatine in a urine specimen. Children with lupus may develop nephrotic syndrome. Children with amyloidosis, a rare complication of juvenile arthritis, often have protein in their urine and also may develop nephrotic syndrome.
Mild amounts of protein in the urine may be an indication that drugs or other chemicals are irritating the kidney. If protein appears in the urine after a new drug has been started, the situation needs careful monitoring. One problem is that certain NSAIDs are excreted in the urine and cause a false positive test for protein on a dipstick (quick) test. This can be determined by having the laboratory perform a more sophisticated test for protein in the urine.
Urobilinogen indicates the presence of bilirubin in the urine. This occurs only in the setting of liver damage or disease that results in an elevated bilirubin level in the blood. This may occur in children with hemolytic anemia because all the broken-down blood cells are metabolized into bilirubin. Another cause of a positive test for urobilinogen is the NSAID etodolac. When etodolac is excreted in the urine, it will react with the test strip and give a false positive test for urobilinogen.
Occult blood in the urine is hemoglobin from broken red blood cells. It suggests that there is bleeding somewhere in the urinary tract. This bleeding may be occurring in the kidney or further down the urinary tract. Most often this is associated with the presence of red blood cells. However, mild bleeding in which all of the cells are broken before leaving the body may show up only as occult blood. Another cause of a positive test for occult blood is myoglobin, a muscle breakdown product that is detected by the dipstick test for occult blood. Myoglobin can show up in the urine after muscle damage from crush injuries or even vigorous tackle football games. It may also be seen in newborn babies who had a difficult delivery. It is rarely present in children with dermatomyositis.
Small amounts of red blood cells in the urine may come from the kidney, the bladder, or anywhere else in the urinary tract. They may be present in the urine after vigorous exercise but should go away quickly. Investigation is necessary if a low level of cells is consistently present. Red blood cells can also appear in the urine if a child is struck hard in the stomach or on the back.
Some children with juvenile arthritis occasionally have blood in their urine without an obvious cause. Blood may also show up in the urine of girls during the time of menstruation. Sometimes a specimen is contaminated with blood just before a girl realizes her period has started. This is not a cause for concern. The specimen simply needs to be repeated after menstruation is over.
Most often a few white blood cells in the urine result from a specimen collected without proper cleansing beforehand. However, large numbers of white blood cells or clumps should be considered an indication of infection, and a urine culture should be performed. White blood cells in the urine may also result from irritation of the kidney.
Casts refer to clumps of red or white blood cells in the urine. They are called "casts" because the clumps take the shape of the urine tubules. If red or white blood cell casts are present, it is considered an indication of ongoing significant kidney damage. This is most often seen in SLE but can occur in other diseases that damage the kidneys. Hyaline casts are another type of cast but are not significant.
Bacteria in the urine suggest that either the specimen was not collected in a clean manner or that there is a urinary tract infection. If there is a urinary tract infection, it is usually due to a single type of bacteria, while a poorly collected specimen may contain many different types of bacteria. A leukocyte esterase test may help in detecting a urine infection, as the level of leukocyte esterase goes up when the white cells (leukocytes) are trying to fight an infection. However, this is not always a reliable finding.
Some compounds that are excreted into the urine by the body may condense into crystals. Uric acid crystals and calcium appetite crystals are very common. If there are a lot of these crystals, one must consider the possibility of kidney stones. These types of crystals are not normally associated with any of the rheumatic diseases.
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