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Tests on urine can provide clues
to many diseases and information about a person's overall health. A routine
urine screening test may be done to help find the cause for many
types of symptoms.
The
kidneys serve to remove waste material, minerals, fluids, and other substances
from the blood for elimination in the urine. Therefore, urine can contain
hundreds of different bodily waste products. Many factors (such as diet, fluid
intake, exercise, and kidney function) affect what is in urine.
Over 100 different tests can be done
on urine. However, a routine urinalysis usually involves the following tests.
Color. Many factors
affect urine color, including fluid balance, diet, medications, or disease. The intensity of the color generally indicates the
concentration of the urine; pale or colorless urine indicates that the urine is dilute, and deep
yellow urine indicates that it is concentrated. Vitamin B supplements can turn urine
bright yellow. Reddish brown urine may be caused by taking certain medications,
eating blackberries or beets, or by the presence of blood in the urine.
Clarity. This test
(also called opacity or turbidity) determines the cloudiness
of the urine. Urine is normally clear. Bacteria, blood,
sperm, crystals, or mucus can make urine appear cloudy.
Odor. Some diseases can cause a change
in the normal odor of urine.
For example, an infection with E. coli
bacteria can cause a foul odor while diabetes or starvation can cause a sweet, fruity odor.
Specific gravity. This measures the amount of substances dissolved in the urine.
It also indicates how well the kidneys are able to adjust the amount of water
in urine. The higher the specific gravity, the more solid material is dissolved
in the urine. When a person drinks a lot of liquid, the
kidneys should produce greater than normal
amounts of dilute urine. When a person drinks very little liquid, the kidneys
should make only small amounts of concentrated urine.
pH. The pH is a measure of how acidic
or alkaline (basic) the urine is. A
urine pH of 4 is strongly acidic, 7 is neutral (neither acidic nor alkaline),
and 9 is strongly alkaline. Sometimes the pH of the urine may be adjusted
by certain types of treatment. For example, efforts may be made to keep urine
either acidic or alkaline to prevent formation of certain types of kidney
stones.
Protein. Normally there is no protein in the urine. Sometimes a small
amount of protein is released into the urine when a person stands up (this
condition is called postural proteinuria). Fever, strenuous exercise, normal
pregnancy, and some diseases (especially kidney disease) may also cause protein
in the urine.
Glucose. Glucose is the type of sugar usually found in blood. Normally
there is very little or no glucose in urine. However, when the blood sugar
level is very high, as in uncontrolled diabetes, it spills over into the urine. Glucose can
also be present in urine when the kidneys are damaged or diseased.
Ketones. When fat is broken
down for energy, the body produces by-products
called ketones (or ketone bodies) and releases them into the urine. Large
amounts of ketones in the urine may signal a dangerous condition known as
diabetic ketoacidosis. A diet low in sugars and starches (carbohydrates),
starvation, or prolonged vomiting may also cause ketones in the urine.
Microscopic analysis.
In this test, urine is spun in a centrifuge
so the solid materials (sediment) settle out. The sediment is spread on a
slide and examined under a microscope. Types of materials that may be found
include:
Red
or white blood cells. Normally blood cells are not found in urine.
Inflammation, disease, or injury to the kidneys, ureters, bladder or urethra
can cause blood in urine. Strenuous exercise (such as running a marathon)
can also cause blood in urine. White blood cells are often a sign of infection,
cancer, or kidney disease.
Casts. Some types of kidney disease can cause plugs of material (called casts)
to form in tiny tubes in the kidneys. The casts can then get flushed out into
the urine. Casts can be made of different types of material, such as red or
white blood cells, waxy or fatty substances, or protein. The type of cast
can provide clues about the type of kidney disease that may be present.
Crystals. Healthy people
often have only a few crystals in their urine. However,
a large number of crystals, or the presence of certain types of crystals,
may indicate kidney stones or a problem with how the body is using food (metabolism).
Bacteria,
yeast cells, or parasites. Normally there are no bacteria, yeast cells,
or parasites in urine. Their presence can indicate an infection.
This test is done on a sample of
urine.
Urine Test Results
Normal results may vary from lab
to lab.
Color
Normal:
Pale
to dark yellow
Abnormal:
Many foods and medications can affect
the color of the urine. Colorless urine may be caused by conditions such as
long-term kidney disease or uncontrolled diabetes. Dark yellow urine can be caused by conditions
such as dehydration. Reddish urine can be caused by blood in the urine.
Clarity
Normal:
Clear
Abnormal:
Cloudy urine can be caused by pus (white blood cells), blood
(red blood cells), sperm, bacteria, yeast, crystals, mucus, or a parasite infection
(such as trichomoniasis).
Odor
Normal:
Slightly
"nutty" (aromatic) odor
Abnormal:
Some foods (such
as asparagus), vitamins, and antibiotics (such as penicillin) can cause urine
to develop an unusual odor. A sweet, fruity odor may be caused by uncontrolled diabetes.
A urinary tract infection (UTI) can cause a foul odor. Urine that smells like
maple syrup can indicate maple syrup urine disease, a condition caused by the body's inability
to break down certain amino acids.
Specific
gravity
Normal:
1.005–1.035
Abnormal:
Abnormally high specific gravity indicates
very concentrated urine, which may be caused by not drinking enough liquid,
loss of too much liquid (excessive vomiting, sweating, or diarrhea), or substances
(such as sugar or protein) in the urine. Abnormally low specific gravity indicates
dilute urine, which may be caused by drinking excessive amounts of liquid,
severe kidney disease, or the use of diuretics.
pH
Normal:
4.5–8.0
Abnormal:
Some foods (such as citrus fruit and
dairy products) and medications (such as antacids) can affect urine pH. A high
(alkaline) pH can be caused by prolonged vomiting, a kidney disease, some
urinary tract infections, and asthma. A low (acidic) pH may be a sign of severe
lung disease (emphysema), uncontrolled diabetes, aspirin overdose, prolonged diarrhea, dehydration,
starvation, drinking an excessive amount of alcohol, or drinking antifreeze
(ethylene glycol).
Protein
Normal:
None
Abnormal:
Protein in the urine usually indicates kidney damage or disease
that can be caused by conditions such as an infection, cancer, high blood
pressure, diabetes, or systemic
lupus erythematosus (SLE). Protein in the urine can also be caused
by heart
failure, leukemia, multiple
myeloma, poison (lead or mercury poisoning), and a condition during
pregnancy resulting in high blood pressure (preeclampsia).
Glucose
Normal:
None
Abnormal:
Some medications can cause glucose in the urine. Excess glucose
in the urine is often caused by uncontrolled diabetes. Other conditions that may cause glucose
in urine include an adrenal
gland problem, liver damage, brain injury, certain types of poisoning,
and certain kidney diseases that decrease their ability to reabsorb glucose
from the urine.
Ketones
Normal:
None
Abnormal:
Ketones in the urine can indicate poorly controlled diabetes,
a very low-carbohydrate diet, starvation (including disorders that result
in poor nutrition such as anorexia nervosa or bulimia), alcoholism, or poisoning from drinking rubbing
alcohol (isopropanol). Ketones are often found in the urine if a person avoids
eating (fasts) for 18 hours or longer. This may occur when a person is sick
and does not eat or vomits for an extended period of time.
Low levels of ketones are sometimes found in the urine of a healthy pregnant
woman.
Microscopic
analysis
Normal:
Very
few or no red or white blood cells or casts. No bacteria, yeast cells, or parasites.
A few crystals are usually normal.
Abnormal:
Red
blood cells in the urine may be caused by kidney or bladder injury, kidney
stones, urinary tract infection, inflammation of the kidneys (glomerulonephritis),
a kidney or bladder tumor, or systemic lupus erythematosus (SLE). White blood cells
(pus) in the urine indicate a urinary tract infection, bladder tumor, glomerulonephritis,
or systemic
lupus erythematosus (SLE).
Depending on the type, casts can indicate inflammation or damage
to the tiny tubes in the kidneys, poor blood supply to the kidneys, metal
poisoning (such as lead or mercury), heart failure, or a bacterial infection.
Excessive amounts of crystals, or the
presence of certain types of crystals, can indicate kidney stones, damaged
kidneys, or problems with metabolism. Some medications
and certain types of urinary tract infections can also increase the number
of crystals in urine.
Bacteria
in the urine indicate a urinary tract infection (UTI). Yeast cells or parasites
(such as the parasite that causes trichomoniasis) can indicate an infection of the urinary
tract.
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