Urinalysis is a diagnostic tool used to examine kidney health by analyzing urine. It involves two stages: gross and microscopic analysis, which can detect abnormalities such as red and white blood cells, bacteria, casts, and crystals. Abnormalities can indicate kidney or urinary tract disease or infection.
Urinalysis is a diagnostic tool commonly used in diagnosing urinary tract disease and other disorders that can affect the kidneys. This is an effective way to examine kidney health because the kidneys filter urine before it is passed out. Examining the contents of your urine can help provide clues about the health of your kidneys. In microscopic urine analysis, a close-up examination of a urine sample is done using a microscope.
Urinalysis generally has two stages: gross urinalysis and microscopic urinalysis. In gross analysis, a urine sample is examined simply by looking at its color, opacity, and other factors such as sugar and protein content. Healthy urine is clear, pale yellow or light amber in color, and does not contain particulate matter. If gross examination shows that the urine is cloudy, of an abnormal color, or contains a high percentage of protein, this can help establish a diagnosis.
In microscopic urine analysis, a small sample of urine is centrifuged to remove fluid. The sediment is then examined under a microscope. In a typical microscopic analysis of urine, a sample is examined for the presence of red and white blood cells, kidney epithelial cells, bacteria, casts, and crystals.
A small number of kidney epithelial cells are usually present in a normal urine sample. These cells are naturally cleared from the tubules of the kidneys as new cells grow. If large numbers of these cells are present in a sample, this is usually an indication of some type of disease in the kidney or upper urinary tract.
The presence of red blood cells in a urine sample can be an indication of several disease processes. These include kidney or urinary tract damage, kidney or urinary tract stones, and urinary tract infection. A small amount of blood is normal in a sample from a menstruating woman or in a sample from a person who has recently had a bladder catheter inserted. In general, red blood cells are not present in urine, and the presence of these cells is almost always an indicator of an abnormal sample.
White blood cells can be present in both normal and abnormal urine samples, but the presence of these cells likely indicates an infection. Generally, white blood cells in a urine sample are an indication of a urinary tract infection or kidney infection. In some cases, a urine sample may be contaminated with white blood cells from the external genital area. When this happens, it is often an indication of an external genital infection.
It is common to find bacteria in a normal urine sample, particularly if the sample was given by a woman or girl. This is because a sample is likely to contain cells and bacteria from the external genital area. Microscopic bacterial analysis of urine therefore involves examining the types of bacteria present in a sample, rather than just the presence of bacteria. In most cases, this requires culturing a urine sample to determine which bacteria are present in sufficient numbers to cause infection.
Casts and crystals are lumps of substances, usually cells or molecules, that are passed in the urine. Casts are congregations of red or white blood cells that have stuck together. Generally, the presence of red blood cell casts indicates a kidney infection or kidney disease of some kind. If white blood cell casts are present, this is a clear indicator of acute kidney infection or inflammation. When crystals are found in a microscopic analysis of urine, this could indicate liver disease, but small numbers of casts are often seen in samples from healthy people.
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