A Urinalysis is a Group of Manual And
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Transcript of A Urinalysis is a Group of Manual And
A urinalysis is a group of manual and/or automated qualitative and
semi-quantitative tests performed on a urine sample. A routine
urinalysis usually includes the following tests: color, transparency,
specific gravity, pH, protein, glucose, ketones, blood, bilirubin,
nitrite, urobilinogen, and leukocyte esterase. Some laboratories
include a microscopic examination of urinary sediment with all
routine urinalysis tests. If not, it is customary to perform the
microscopic exam, if transparency, glucose, protein, blood, nitrite,
or leukocyte esterase is abnormal.
Purpose
Routine urinalyses are performed for several reasons:
general health screening to detect renal and metabolic diseases
diagnosis of diseases or disorders of the kidneys or urinary
tract
monitoring of patients with diabetes
In addition, quantitative urinalysis tests may be performed to help
diagnose many specific disorders, such as endocrine diseases,
bladder cancer, osteoporosis, and porphyrias (a group of disorders
caused by chemical imbalance). Quantitative analysis often requires
the use of a timed urine sample. The urinary microalbumin test
measures the rate of albumin excretion in the urine using laboratory
tests. This test is used to monitor the kidney function of persons
with diabetes mellitus. In diabetics, the excretion of greater than
200 μg/mL albumin is predictive of impending kidney disease.
Precautions
Voided specimens
All patients should avoid intense athletic training or heavy physical
work before the test, as these activities may cause small amounts of
blood to appear in the urine. Many urinary constituents are labile,
and samples should be tested within one hour of collection or
refrigerated. Samples may be stored at 36–46°F (2–8°C) for up to
24 hours for chemical urinalysis tests; however, the microscopic
examination should be performed within four hours of collection, if
possible. To minimize sample contamination, women who require a
urinalysis during menstruation should insert a fresh tampon before
providing a urine sample.
Over two dozen drugs are known to interfere with various chemical
urinalysis tests. These include:
ascorbic acid
chlorpromazine
L-dopa
nitrofurantoin (Macrodantin, Furadantin)
penicillin
phenazopyridine (Pyridium)
rifampin (Rifadin)
tolbutamide
The preservatives that are used to prevent loss of glucose and cells
may affect biochemical test results. The use of preservatives should
be avoided whenever possible in urine tests.
Description
Routine urinalysis consists of three testing groups: physical
characteristics, biochemical tests, and microscopic evaluation.
Physical tests
The physical tests measure the color, transparency (clarity), and
specific gravity of a urine sample. In some cases, the volume (daily
output) may be measured. Color and transparency are determined
from visual observation of the sample.
COLOR. Normal urine is straw yellow to amber in color. Abnormal
colors include bright yellow, brown, black (gray), red, and green.
These pigments may result from medications, dietary sources, or
diseases. For example, red urine may be caused by blood or
hemoglobin, beets, medications, and some porphyrias. Black-gray
urine may result from melanin (melanoma) or homogentisic acid
(alkaptonuria, a result of a metabolic disorder). Bright yellow urine
may be caused by bilirubin (a bile pigment). Green urine may be
caused by biliverdin or certain medications. Orange urine may be
caused by some medications or excessive urobilinogen (chemical
relatives of urobilinogen). Brown urine may be caused by excessive
amounts of prophobilin or urobilin (a chemical produced in the
intestines).
TRANSPARENCY. Normal urine is transparent. Turbid (cloudy)
urine may be caused by either normal or abnormal processes.
Normal conditions giving rise to turbid urine include precipitation
of crystals, mucus, or vaginal discharge. Abnormal causes of
turbidity include the presence of blood cells, yeast, and bacteria.
SPECIFIC GRAVITY. The specific gravity of urine is a measure of the
concentration of dissolved solutes (substances in a solution), and it
reflects the ability of the kidneys to concentrate the urine (conserve
water). Specific gravity is usually measured by determining the
refractive index of a urine sample (refractometry) or by chemical
analysis. Specific gravity varies with fluid and solute intake. It will
be increased (above 1.035) in persons with diabetes mellitus and
persons taking large amounts of medication. It will also be increased
after radiologic studies of the kidney owing to the excretion of x ray
contrast dye. Consistently low specific gravity (1.003 or less) is seen
in persons with diabetes insipidus. In renal (kidney) failure, the
specific gravity remains equal to that of blood plasma (1.008–1.010)
regardless of changes in the patient's salt and water intake. Urine
volume below 400 mL per day is considered oliguria (low urine
production), and may occur in persons who are dehydrated and
those with some kidney diseases. A volume in excess of 2 liters
(slightly more than 2 quarts) per day is considered polyuria
(excessive urine production); it is common in persons with diabetes
mellitus and diabetes insipidus.
Biochemical tests
Biochemical testing of urine is performed using dry reagent strips,
often called dipsticks. A urine dipstick consists of a white plastic
strip with absorbent microfiber cellulose pads attached to it. Each
pad contains the dried reagents needed for a specific test. The
person performing the test dips the strip into the urine, lets it sit for
a specified amount of time, and compares the color change to a
standard chart.
Additional tests are available for measuring the levels of bilirubin,
protein, glucose, ketones, and urobilinogen in urine. In general,
these individual tests provide greater sensitivity; they therefore
permit detection of a lower concentration of the respective
substance. A brief description of the most commonly used dry
reagent strip tests follows.
pH: A combination of pH indicators (methyl red and bromthymol
blue) react with hydrogen ions (H + ) to produce a color change over
a pH range of 5.0 to 8.5. pH measurements are useful in
determining metabolic or respiratory disturbances in acid-base
balance. For example, kidney disease often results in retention of
H+ (reduced acid excretion). pH varies with a person's diet, tending
to be acidic in people who eat meat but more alkaline in vegetarians.
pH testing is also useful for the classification of urine crystals.
Protein: Based upon a phenomenon called the "protein error of
indicators," this test uses a pH indicator, such as tetrabromphenol
blue, that changes color (at constant pH) when albumin is present in
the urine. Albumin is important in determining the presence of
glomerular damage. The glomerulus is the network of capillaries in
the kidneys that filters low molecular weight solutes such as urea,
glucose, and salts, but normally prevents passage of protein or cells
from blood into filtrate. Albuminuria occurs when the glomerular
membrane is damaged, a condition called glomerulonephritis.
Glucose (sugar): The glucose test is used to monitor persons with
diabetes. When blood glucose levels rise above 160 mg/dL, the
glucose will be detected in urine. Consequently, glycosuria (glucose
in the urine) may be the first indicator that diabetes or another
hyperglycemic condition is present. The glucose test may be used to
screen newborns for galactosuria and other disorders of
carbohydrate metabolism that cause urinary excretion of a sugar
other than glucose.
Ketones: Ketones are compounds resulting from the breakdown of
fatty acids in the body. These ketones are produced in excess in
disorders of carbohydrate metabolism, especially Type 1 diabetes
mellitus. In diabetes, excess ketoacids in the blood may cause life-
threatening acidosis and coma. These ketoacids and their salts spill
into the urine, causing ketonuria. Ketones are also found in the
urine in several other conditions, including fever; pregnancy;
glycogen storage diseases; and weight loss produced by a
carbohydrate-restricted diet.
Blood: Red cells and hemoglobin may enter the urine from the
kidney or lower urinary tract. Testing for blood in the urine detects
abnormal levels of either red cells or hemoglobin, which may be
caused by excessive red cell destruction, glomerular disease, kidney
or urinary tract infection, malignancy, or urinary tract injury.
Bilirubin: Bilirubin is a breakdown product of hemoglobin. Most of
the bilirubin produced in humans is conjugated by the liver and
excreted into the bile, but a very small amount of conjugated
bilirubin is reabsorbed and reaches the general circulation to be
excreted in the urine. The normal level of urinary bilirubin is below
the detection limit of the test. Bilirubin in the urine is derived from
the liver, and a positive test indicates hepatic disease or
hepatobiliary obstruction.
Specific gravity: Specific gravity is a measure of the ability of the
kidneys to concentrate urine by conserving water.
Nitrite: Some disease bacteria, including the lactose-
positive Enterobactericeae, Staphylococcus, Proteus,
Salmonella, and Pseudomonas are able to reduce nitrate in urine to
nitrite. A positive test for nitrite indicates bacteruria, or the
presence of bacteria in the urine.
Urobilinogen: Urobilinogen is a substance formed in the
gastrointestinal tract by the bacterial reduction of conjugated
bilirubin. Increased urinary urobilinogen occurs in prehepatic
jaundice (hemolytic anemia), hepatitis, and other forms of hepatic
necrosis that impair the circulation of blood in the liver and
surrounding organs. The urobilinogen test is helpful in
differentiating these conditions from obstructive jaundice, which
results in decreased production of urobilinogen.
Leukocytes: The presence of white blood cells in the urine usually
signifies a urinary tract infection, such as cystitis, or renal disease,
such as pyelonephritis or glomerulonephritis.
Microscopic examination
A urine sample may contain cells that originated in the blood, the
kidney, or the lower urinary tract. Microscopic examination of
urinary sediment can provide valuable clues regarding many
diseases and disorders involving these systems.
The presence of bacteria or yeast and white blood cells helps to
distinguish between a urinary tract infection and a contaminated
urine sample. White blood cells are not seen if the sample has been
contaminated. The presence of cellular casts (casts containing RBCs,
WBCs, or epithelial cells) identifies the kidneys, rather than the
lower urinary tract, as the source of such cells. Cellular casts and
renal epithelial (kidney lining) cells are signs of kidney disease.
The microscopic examination also identifies both normal and
abnormal crystals in the sediment. Abnormal crystals are those
formed as a result of an abnormal metabolic process and are always
clinically significant. Normal crystals are formed from normal
metabolic processes; however, they may lead to the formation of
renal calculi, or kidney stones.
Preparation
A urine sample is collected in an unused disposable plastic cup with
a tight-fitting lid. A randomly voided sample is suitable for routine
urinalysis, although the urine that is first voided in the morning is
preferable because it is the most concentrated. The best sample for
analysis is collected in a sterile container after the external genitalia
have been cleansed using the midstream void (clean-catch) method.
This sample may be cultured if the laboratory findings indicate
bacteruria.
To collect a sample using the clean-catch method:
Females should use a clean cotton ball moistened with
lukewarm water (or antiseptic wipes provided with collection
kits) to cleanse the external genital area before collecting a
urine sample. To prevent contamination with menstrual blood,
vaginal discharge, or germs from the external genitalia, they
should release some urine before beginning to collect the
sample.
Males should use a piece of clean cotton moistened with
lukewarm water or antiseptic wipes to cleanse the head of the
penis and the urethral meatus (opening). Uncircumcised males
should draw back the foreskin. After the area has been
thoroughly cleansed, they should use the midstream void
method to collect the sample.
For infants, a parent or health care worker should cleanse the
baby's outer genitalia and surrounding skin. A sterile collection
bag should be attached to the child's genital area and left in
place until he or she has urinated. It is important to not touch
the inside of the bag, and to remove it as soon as a specimen
has been obtained.
Urine samples can also be obtained via bladder catheterization, a
procedure used to collect uncontaminated urine when the patient
cannot void. A catheter is a thin flexible tube that a health care
professional inserts through the urethra into the bladder to allow
urine to flow out. To minimize the risk of infecting the patient's
bladder with bacteria, many clinicians use a Robinson catheter,
which is a plain rubber or latex tube that is removed as soon as the
specimen is collected. If urine for culture is to be collected from an
indwelling catheter, it should be aspirated (removed by suction)
from the line using a syringe and not removed from the bag in order
to avoid contamination.
Suprapubic bladder aspiration is a collection technique sometimes
used to obtain urine from infants younger than six months or urine
directly from the bladder for culture. The doctor withdraws urine
from the bladder into a syringe through a needle inserted through
the skin.
Aftercare
The patient may return to normal activities after collecting the
sample and may start taking any medications that were
discontinued before the test.
Risks
There are no risks associated with voided specimens. The risk of
bladder infection from catheterization with a Robinson catheter is
about 3%.
Normal results
Normal urine is a clear straw-colored liquid, but may also be slightly
hazy. It has a slight odor, and some laboratories will note strong or
atypical odors on the urinalysis report. A normal urine specimen
may contain some normal crystals as well as squamous or
transitional epithelial cells from the bladder, lower urinary tract, or
vagina. Urine may contain transparent (hyaline) casts, especially if
it was collected after vigorous exercise . The presence of hyaline
casts may be a sign of kidney disease, however, when the cause
cannot be attributed to exercise, running, or medications. Normal
urine contains a small amount of urobilinogen, and may contain a
few RBCs and WBCs. Normal urine does not contain detectable
amounts of glucose or other sugars, protein, ketones, bilirubin,
bacteria, yeast cells, or trichomonads. Normal values used in many
laboratories are given below:
Glucose: negative (quantitative less than 130 mg/day or 30
mg/dL).
Bilirubin: negative (quantitative less than 0.02 mg/dL).
Ketones: negative (quantitative 0.5–3.0 mg/dL).
pH: 5.0–8.0.
Protein: negative (quantitative 15–150 mg/day, less than 10
mg/dL).
Blood: negative.
Nitrite: negative.
Specific gravity: 1.015–1.025.
Urobilinogen: 0–2 Ehrlich units (quantitative 0.3–1.0 Ehrlich
units).
Leukocyte esterase: negative.
Red blood cells: 0–2 per high power field.
White blood cells: 0–5 per high power field (0–10 per high
power field for some standardized systems).
Resources
BOOKS
Chernecky, Cynthia C, and Barbara J. Berger. Laboratory Tests and
Diagnostic Procedures , 3rd ed. Philadelphia, PA: W. B. Saunders
Company, 2001.
Henry, J.B. Clinical Diagnosis and Management by Laboratory
Methods , 20th ed. Philadelphia, PA: W.B. Saunders Company,
2001.
Kee, Joyce LeFever. Handbook of Laboratory and
Diagnostic Tests , 4th ed. Upper Saddle River, NJ: Prentice Hall,
2001.
Wallach, Jacques. Interpretation of Diagnostic Tests , 7th ed.
Philadelphia, PA: Lippincott Williams & Wilkens, 2000.
Read more: http://www.surgeryencyclopedia.com/St-
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