CLINICAL LAB SCIENEC

CHAPTER 12: PROCEDURES FOR URINALYSIS AND BODY FLUIDS 289
of the symptoms and signs the patient exhibits. The complete urinalysis is one
of these basic tests that are performed at one time or another on almost all
patients. A urinalysis gives the physician or other medical practitioner, such as
a nurse practitioner or physician’s assistant, a screening test that may immediately
indicate a disease process. An abnormal positive finding on a random
urine specimen will necessitate further testing and evaluation to rule out a number
of diseases that cause changes in the various body systems that rid the body
of excess water and waste products. Sometimes, testing for metabolic end-point
products that indicate genetic disorders may be required, and while these tests
are usually sent to a reference laboratory, certain clues may be found in the
urinalysis to indicate a need for referring the sample to a specialized laboratory.
It would be advisable to review the urinary (renal) system from anatomy and
physiology course books to ensure a thorough understanding of the role the
kidneys play in health (Figure 12-1). Body fluids other than blood and urine
that are candidates for laboratory testing include cerebrospinal fluid (CSF), synovial
fluid from joints, gastric contents from the stomach, and fluids that may
accumulate in body compartments.
Urine samples are relatively easy to collect. Several basic tests using urine as
the sample will yield much important information regarding the anatomy and
physiology of the renal system. Although a large number of tests are possible,
only the most basic will be presented here. Specimens may be “random,” giving
a snapshot of the current condition of the patient. Because a more dilute sample
may give erroneous results, it is sometimes necessary to collect an early morning
sample that is concentrated. This would
give a more accurate picture of a medical
condition where there is normally a small
amount of certain components and these
levels would be increased in an unhealthy
patient. For some laboratory procedures and
certain quantitative tests, the entire volume
of urine excreted in a 24-hour period may
be required. For other laboratory examinations,
specimens may need to be collected at
timed intervals, such as at 2 hours following
the administration of food or medication.
Certain hormones control blood formation
and help to retain or excrete various ions
(chemical components), so damage to the
kidneys can affect the body in many ways.
Some specimens may require preservatives
(Table 12-1) to prevent growth of bacteria
or a change in the pH, which might destroy
some analytes (components being tested for).
All of these conditions would be discussed in
a course textbook that specifically covers urinalysis
and body fluids.
Bowman’s
capsule
Efferent
arteriole
Glomerulus
Interlobular
artery
Interlobular
vein
Afferent
arteriole
Juxtaglomerular
apparatus
Peritubular capillaries
Descending limb—loop
of Henle
Proximal convoluted tubule
Distal
convoluted
tubule
Collecting
tubule
Ascending limb—
loop of Henle
FIGURE 12-1 A nephron of the kidney involved with production of urine.
Source: Delmar/Cengage Learning.
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