Under The Microscope
Urine analysis is the term
used to refer to the test used to evaluate a urine sample. Typically, this test
is used for the purposes of assessing a wide range of disorders, which may
include kidney disease, urinary tract infection (UTI) dehydration as well as diabetes.
The test will involve an examination of the appearance, concentration as well
as content of the urine sample.
In microscopy, a sample of urine is centrifuged to obtain some sediment, which can then used to examine the presence of crystals, casts, white and/or red blood cells or bacteria/yeast infection.
While the appearance or coloration can give some indication of the problem, microscopy allows for a deeper urine analysis, which would prove useful for diagnosis and prognosis.
Urine Analysis and Sample Collection
For the purposes of
microscopic urine analysis, the first morning specimen is the recommended specimen of
choice. This due to the fact that it is generally more concentrated because of
the amount of time it remained in the bladder.
As such, the sample would
contain relatively higher amounts of such analytes as proteins or other
cellular elements if at all they are present. To prevent any form of contamination,
a midstream clean catch specimen is recommended.
Here, the patient/participant
will be required to start by cleansing the urethral area using a castile soap towelette
(or simply cleansed and rinsed well) A small amount of urine should then be
voided in to the toilet in order to reduce the changes of contaminants from
entering in to the collecting container before collecting the rest midstream in
to the clean container.
Once the sample of urine
has been properly collected:
- Pour 10 to 15 ml of the well-mixed urine in to a test tube and
place it in the centrifuge (the test tube should always be balanced with a
second test tube filled with water/another urine sample) of equal volume
- Centrifuge the sample at low speeds of between 2,000 to 3,000
rounds per minute for about 7 minutes,
- Decant the supernate (to retain about 0.2- 0.5 ml inside the tube)
- Shake the tube to mix the sediment and supernate retained in the
- Using a pipette, collect and place a drop of the re-suspended
sediment on to a microscopic slide and place a cover slip over the drop for
Note** If the urine sample
is not analyzed within 2 hours after collection, it should be stored for not
more than 24 hours (refrigeration).
On the other hand, such
chemicals as boric acid and tartaric acid may be used for preservation
purposes. This allows for the urine to be kept at room temperature, and still
provide similar results as refrigerated urine.
Preservation is important in
that it allows for a stable environment for the specimen while reducing the
risks of bacterial overgrowth or decomposition.
Multiple white cells present in the urine of person with a urinary tract infection using microscopy By Bobjgalindo - Own work, GFDL, https://commons.wikimedia.org/w/index.php?curid=5652287
For urine analysis, the sediment should first
be observed under low power when observing for crystals, casts, squamous cells
or other larger objects. When making a report, the number of casts seen under
the microscope is usually reported as the number of each type per low power
field. Moreover, low power allows for a wider view, which allows for clear
observation of the number of casts seen.
To observe and identify
cells, crystals and bacteria, high power is used. In this case, the types of
cells will also be described as the number of each type found per the high
Note** - When observing the
slide under low power, low light source should be used. This is because of the
fact that too much light would make it more difficult to see he cellular and crystalline
Typically, early morning
sample before the ingestion of a liquid is preferred since it reflects the ability
of the kidney to concentrate urine during dehydration, over a period of about 8
hours (during sleep).
On the other hand, random collection may be taken at a given
time of the day without precaution with regards to contamination. Such samples
may be isotonic, dilute, containing white cells or even bacteria among others.
During collection, voiding
first half of the urine is recommended in order to flush out any possible
contaminants (cells or microbes) which may still be present on the outer of the
urethra. It therefore makes the urine analysis easier by eliminating any
contaminants that may lead poor diagnosis and prognosis.
In this case,
therefore, the technician only gets to observe and analyze the contents of the
Depending on the urine as
well as how it was collected, the microscopic examination of the sediment may
detect the presence of the following:
- Red blood cells - Except in certain situations like during menstruation
among women, no red blood cells should be present in a urine sample.
- White blood cells - The presence of white blood cells in urine is
indicative of an infection.
- Epithelial cells - These cells normally slough in to the urine and
can be seen in a urine sample. They include transitional and squamous epithelial
- Casts - Cylindrical structures produced in the kidney. They are
present in urine in certain disease states.
- Bacteria - Bacteria are common in urine. However, the significant
numbers may be indicative of an infection.
- Yeast - Yeast may either be contaminants or representative of true
- Crystals - Crystals can be seen even in urine from a healthy
person. They include triple phosphate crystals, calcium oxalate and amorphous
Urine is a bio-fluid, which
means that it is a fluid that originates from inside the body. As such; it
should be handled with care. While care should be taken while collecting a
urine sample to avoid contaminating it, it should also be handled with care
while examining. This is a safety precaution that should involve the use of
Moreover, all the remaining fluids should be discarded safely.
Although urine samples are not considered biohazard under the OSHA
regulations/standards, it should be safely discarded in the laboratory sink and
washed away with water.
While this experiment is easy with a lot to show,
inexperienced students should be supervised to get the best results possible.
Related: Hematuria - Micrscopy of Urine and Observations
More on Leukocytes here
Of Interest: Sputum Microscopy, Blood Microscopy
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