2. Urine formation
In an adult, urine output volume ranges from 400 to
2,000 mL/day.
Overview.
◻ Approximately 1,200 mL of blood per minute (i.e.,
20%–25% of blood volume) is supplied to the kidneys
through the renal artery, which branches into the
afferent arterioles and efferent arterioles.
3. Constituents of urine
◻ Urine is continuously formed by the kidneys. Depending on dietary
intake, physical activity, metabolism and endocrine function,
concentrations of urine constituents vary.
◻ The largest component of urine is water.
◻ Urea accounts for half of the total dissolved solids in urine (6–18
g/24 h). It is
a metabolic waste product from the breakdown of protein and
amino acids in the liver.
◻ Other organic compounds in urine are creatinine (0.3–0.8 g/24 h)
and uric acid
(0.08–0.2 g/24 h). A fluid can be identified as urine if it contains a
high concentration of urea and creatinine.
◻ Chloride (100–250 mEq/24 h) is the major inorganic solid dissolved
in urine, followed by sodium (100–200 mEq/24 h) and potassium
(50–70 mEq/24 h).
◻ In urinary sediment, a few squamous, transitional, and renal
epithelial cells per high power field (40X) as well as one to two red
blood cells (RBCs) or one to five white blood cells (WBCs) are
4. THE URINE SPECIMEN
◻ Routine urinalysis testing describes the results of a series of screening
tests capable of detecting (in a semi-quantitative manner) renal,
urinary tract, metabolic and systemic diseases. Urine is readily
available and easy to collect.
1. When there is disease of the kidney or bladder, kidney function may be
impaired. Substances that are normally retained by the kidney may be
excreted, and substances that are normally excreted may be retained.
The routine urinalysis is a good screening test for the detection of
changes in renal system.
2. Metabolic or systemic diseases may lead to the excretion of
substances such as abnormal amounts of metabolic end products or
substances specific for a particular disease that can be detected in
urine. The amount of sodium or water that is excreted is also indicative
of systemic or metabolic disease.
3. All body fluid specimens should be considered infectious and collected,
transported, and handled according to safety protocols.
4. Urine specimens should be analyzed within 1 hour of collection, or they
must be stored in a dark refrigerator between 4◦C and 7◦C to preserve
chemical and cellular constituents.
5. Random Specimen
◻ This is the most commonly received specimen
because of its ease of collection and
convenience for the patient.
◻ The random specimen may be collected at
any time, but the actual time of voiding should
be recorded on the container.
◻ The random specimen is useful for routine
screening tests to detect obvious
abnormalities
6. First Morning Specimen
◻ The first morning specimen, or 8-hour
specimen, is a concentrated specimen,
thereby assuring detection of chemicals and
formed elements that may not be present in a
dilute random specimen.
◻ The patient should be instructed to collect the
specimen immediately on arising and to
deliver it to the laboratory within 2 hours.
◻ It is also essential for preventing false-negative
pregnancy tests and for evaluating orthostatic
proteinuria.
7. 24-Hour (Timed) Specimen
Collection
Procedure
◻ Provide patient with written instructions, and explain
collection procedure.
◻ Issue proper collection container and preservative.
◻ Day 1: 7 a.m.: patient voids and discards specimen; collects
all urine for the next 24 hours.
◻ Day 2: 7 a.m.: patient voids and adds this urine to previously
collected urine.
◻ On arrival at laboratory, the entire 24-hour specimen is
thoroughly mixed, and the volume is measured and
recorded.
◻ An aliquot is saved for testing and additional or repeat
testing; discard remaining urine.
8. ◻ Measuring the exact amount of a urine
chemical is often necessary instead of just
reporting its presence or absence.
◻ A carefully timed specimen must be used to
produce accurate quantitative results.
◻ A 24-hour specimen must be thoroughly mixed
and the volume accurately measured and
recorded.
9. Urine Preservatives
Preservatives Advantages Disadvantages Additional Information
Refrigeration Does not interfere with
chemical tests
Raises specific gravity
by hydrometer
Precipitates amorphous
phosphates and urates
Prevents bacterial
growth
24 h
Thymol Preserves glucose and
sediments well
Interferes with acid
precipitation tests for
protein
Boric acid Does not interfere with
routine analyses other
than pH.
Preserves protein and
formed elements well
May precipitate crystals
when used in large
amounts
Keeps pH at about 6.0. Is
bacteriostatic (not
bactericidal) at 18 g/L;
can use for culture
transport Interferes with
drug and hormone
analyses
Formalin
(formaldehyde
Excellent sediment
preservative
Acts as a reducing
agent, interfering with
chemical tests for
glucose, blood,
leukocyte esterase, and
copper reduction
Rinse specimen
container
with formalin to preserve
cells and casts
Toluene Does not interfere with
routine tests
Floats on surface of
specimens and clings to
10. Chemical Examination of Urine
◻ pH
◻ Specific Gravity
◻ Protein
◻ Glucose
◻ Ketone
◻ Bilirubin
◻ Urobilinogen
11. pH
◻ To differentiate pH units double-indicator system
of methyl red and bromthymol blue.
◻ Methyl red produces a color change from red to
yellow in the pH range 4 to 6, and bromthymol blue
turns from yellow to blue in the range of 6 to 9.
◻ Therefore, in the pH range 5 to 9 measured by the
reagent strips, one sees colors progressing from
orange at pH 5 through yellow and green to a final
deep blue at pH 9.
Methyl red H+ → Bromthymol blue H+
(Red-Orange → Yellow) (Green → Blue)
15. Odur Causes
of Urine
Odor Cause
Aromatic Normal
Foul , ammonia-like Bacterial decomposition urinary tract
infection
Fruity, sweet Ketones (diabetes mellitus,
starvation, vomiting
Maple syrup Maple syrup urine disease
Mousy Phenylketonuria
Rancid Tyrosinemia
Cabbage Methionine malabsorption
16. Clinical Significance of Urine pH
1. Respiratory or metabolic acidosis/ketosis
2. Respiratory or metabolic alkalosis
3. Defects in renal tubular secretion and
reabsorption of acids and bases—renal
tubular acidosis
4. Renal calculi formation
5.Treatment of urinary tract infections
6. Precipitation/identification of crystals
7. Determination of unsatisfactory specimens
17. Specific Gravity
◻ Reaction is based on the change in pka (dissociation
constant) of a polyelectrolyte in an alkaline medium.
◻ The polyelectrolyte ionizes, releasing hydrogen ions in
proportion to the number of ions in the solution.
◻ The higher the concentration of urine, the more
hydrogen ions are released, thereby lowering the pH.
Incorporation of the indicator bromthymol blue on the
reagent pad measures the change in pH.
◻ As the specific gravity increases, the indicator
changes from blue (1.000 [alkaline]), through shades of
green, to yellow (1.030 [acid]).
◻ Readings can be made in 0.005 intervals by careful
comparison with the color chart.
18. Clinical Significance of Urine Specific
Gravity
1. Monitoring patient hydration and dehydration
2. Loss of renal tubular concentrating ability
3. Diabetes insipidus
4. Determination of unsatisfactory specimens
due to low concentration
19. Protein
◻ The general belief that indicators produce specific colors
in response to particular pH levels, certain indicators
change color in the presence of protein even though the pH
of the medium remains constant.
◻ This is because protein (primarily albumin) accepts
hydrogen ions from the indicator.
◻ The test is more sensitive to albumin because albumin
contains more amino groups to accept the hydrogen ions
than other proteins
◻ Tetrabromphenol blue and an acid buffer to maintain the pH
at a constant level.
◻ At a pH level of 3, both indicators appear yellow in the
absence of protein; however, as the protein concentration
increases, the color progresses through various shades of
green and finally to blue.
◻ Readings are reported in terms of negative, trace, 1, 2, 3,
and 4
21. Glucose
Glucose Oxidase Reactions
◻ In the first step, glucose oxidase catalyzes a reaction
between glucose and room air to produce gluconic acid
and peroxide.
◻ In the second step, peroxidase catalyzes the reaction
between peroxide and chromogen to form an oxidized
colored compound that represents the presence of
glucose.
23. Ketones
The sodium nitroprusside (nitroferricyanide) reaction
◻ In this reaction, acetoacetic acid in an alkaline medium reacts with
sodium nitroprusside to produce a purple color.
◻ The test does not measure beta-hydroxybutyric acid and is only
slightly sensitive to acetone when glycine is also present; however,
inasmuch as these compounds are derived from acetoacetic acid,
their presence can be assumed, and it is not necessary to perform
individual tests.
◻ Results are reported qualitatively as
negative, trace, small (1), moderate (2), or large (3), .
alkaline acetoacetate + sodium nitroprusside + (glycine) → purple
color
(and acetone)
25. Bilirubin
◻ THE DIAZO REACTION
◻ Bilirubin combines with 2,4-dichloroaniline diazonium
salt or 2,6-dichlorobenzene-diazonium-
tetrafluoroborate in an acid medium to produce an
azodye, with colors ranging from increasing degrees of
tan or pink to violet, respectively.
◻ Qualitative results are reported as
negative, small, moderate, or large, or as negative, 1+,
2+, or3+.
bilirubin glucuronide + diazonium salt azodye
aci
d
26. Clinical Significance of Urine
Bilirubin
1. Hepatitis
2. Cirrhosis
3. Other liver disorders
4. Biliary obstruction (gallstones, carcinoma)
27. Urobilinogen
◻ Ehrlich’s aldehyde reaction
◻ In which urobilinogen reacts with p-dimethylaminobenzaldehyde
(Ehrlich reagent) to produce colors ranging from light to dark pink.
urobilinogen + p-dimethylaminobenzaldehyde → red color
(Ehrlich reagent (Ehrlich reagent)
reactive
substances)
Clinical Significance of Urine Urobilinogen
1. Early detection of liver disease
2. Liver disorders, hepatitis, cirrhosis, carcinoma
3. Hemolytic disorders
