Specific Gravity (SG)
o
SG
measures the density and # of particles
o
SG
can be used to determine the concentrating & diluting
ability of the kidney (this allows the kidneys to
maintain fluid homeostasis)
o
Normal SG = 1.005 – 1.030 (vs. the SG of H2O is 1, and
increases with the addition of glucose & protein)
o
If
there is glucose, protein, or contrast material in the
urine sample, you would want to use osmolality as a
better measurement
(osmolality is a colligative property, meaning it
reflects only the # of particles present in a sample)
Normal osmolality = 50-1200 mOsm/kg H20
(this wide range is the protective mechanism of the
kidney to make urine either very dilute or very
concentrated, depending on the conditions)
pH
o
Reflects the degree of urinary acidification
o
Normal pH = 4.5 – 6.5
o
If a
patient has kidney disease, they may retain hydrogen
ions thus alkalating the urine and causing metabolic
acidosis. Other conditions will cause excess excretion
of hydrogen ions, thus acidifying the urine.(more
acid-base stuff in later lectures!)
This is clinically useful to diagnose renal tubular
acidosis (RTA)
Glucose
o
Not
normally detectable amts
in urine (b/c it's normally reabsorbed in the proximal
tubule)
o
Used
to detect uncontrolled diabetes mellitus
o
Also
used to detect Fanconi syndrome, which is a
proximal tubular defect that is common in pediatric
population, not adults
And remember that pregnancy will cause glucose to
show in the urine NORMALLY due to increased GFR &
glucose filtration!
Protein
o
Reagent strips (dipsticks) detect only albumin
o
Normal protein excretion <150 mg/day
o
To
detect other types of protein, use SSA (sulfosalicyclic
acid)
*Negative
dipstick but positive SSA indicates the presence of
proteins in the urine other than albumin - used as
diagnostic test of multiple myeloma & other plasma cell
dyscrasias)
Ketones
o
3
types of ketones that may be found in urine using
dipstick are acetone, acetoacetic acid (AcAc), and
3-beta hydroxybutyric acid (BHB)
Conditions with these ketones include diabetic
ketoacidosis, starvation ketosis, alcoholic ketosis,
and recovery from ketosis
Blood**
o
Detects hemoglobin & myoglobin hematuria
o
Positive dipstick urine, but no RBCs in sediment
suggests myoglobinuria or hemoglobinuria this can be
diagnostic for rhabdomyolysis
Urinary Sediment
o
This
involves spinning down urine @ 3000rpm for 5 minutes
then removing supernatant.
o
In
this we can find cells, casts, crystals, bacteria,
yeast & miscellaneous.
o
Cell
types
include:
-
squamous epithelial (flat) cells from the urethra
- non pathognomonic, just a contaminated sample
-
transitional (spindle, pear-shaped) cells from the
bladder - may indicate cystitis
-
renal tubular cells from the renal tubules - this may
indicate renal tubule necrosis
-
RBC
and WBC
o
Casts are basically protein made in the Thick Ascending
Loop,
called Tamm-Horsfall protein…they
come in a variety of flavors:
–
Hyaline, granular, RTC, RBC, WBC, Waxy, Broad, Fatty
(Holly’s notes for the next hour include pictures of
these! No worries)
o
Crystals
that we are responsible for knowing are:
-
calcium oxalate (envelope-like appearance) -
nonpathognomic
-
triple phosphate (PO4) (coffin-lid appearance) -
suggests infection
-
uric
acid (football shaped) - nonpathognomonic
-
cystine (benzene ring shaped) - suggests
cystinuria
Back to the Excretory System Index
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