Diagnosis of Diseases of the Urogenital System
History
Several historical
complaints may lead one to suspect that the patient has an abnormality of the
urinary or genital system. Non-leading questions should be asked to obtain
information if it is not volunteered by the owner.
Nonspecific historical
complaints of urinary or genital tract disease may include depression, anorexia,
weight loss, vomiting, or diarrhea. Polyuria (increased urine output) /
polydipsia (increased water intake) (PU/PD) may be owner complaints observed in
patients with acute renal failure (ARF), chronic renal failure (CRF), or
several nonrenal diseases.
Nocturia (urination at
night) may be observed and may
- reflect PU/PD
- be due to urinary
incontinence not related to PU/PD
- or may reflect
pollakiuria
Pollakiuria is increased
frequency of urination, usually with a small volume in each urination.
Pollakiuria signifies the presence of a disease of the lower
urinary tract (bladder and urethra) or the lower genital tract (vagina, penis).
A narrowing in the
diameter of the urine stream may be due to partial obstruction of the urethra by
strictures, calculi, or masses.
Stranguria (painful
urination) and dysuria (difficult urination), are often used inter changeably
and like pollakiuria, are indicative of the presence of lower urinary or genital tract disease.
Hematuria (blood in the
urine) may originate from any part of the urinary or genital tracts. Hematuria
may also occur in patients with bleeding disorders related to platelet function
or number, in the absence of disease of the urinary tract.
Physical examination
The physical examination
of patients with urogenital tract disorders may reveal a variety of problems or
the patient may appear normal upon examination. Weight loss and poor body
condition often accompany chronic renal failure whereas patients with acute
disease are more likely to be in good general physical condition. Dehydration
may be seen in patients with acute or chronic renal failure or dehydration may
be the cause of acute renal failure.
Subcutaneous edema,
ascites or pleural effusion may occur in animals with protein losing states
which result in hypoalbuminemia and reduced oncotic pressure. Although edema
formation (which may also be called "third space fluid accumulation") can occur
in any location, there tends to be species differences in the location of fluid
accumulation. Cats are more likely to develop pleural fluid and dogs are more
likely to develop ascites and subcutaneous fluid accumulation.
Fever is sometimes
observed in patients with acute pyelonephritis, prostatitis and pyometra
although all of these conditions can occur in normothermic patients as well,
especially if the disease is chronic.
Examination of the oral
cavity may reveal the following:
- Mucous membranes may
be pale in CRF patients which are often anemic. Pale mucous membranes may
indicate hypovolemic shock, which due to reduced renal perfusion can lead to
acute renal failure (ARF).
- Loose teeth may
indicate renal osteodystrophy and softening of the bones of the jaws.
Remember that most geriatric patients will have some degree of dental
disease so loose teeth may not be due to renal disease.
- Oral ulcers may be
present in uremic patients and are due to the catabolism of urea in saliva
to ammonia. Ulcers are often associated with a foul mouth odor.
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The kidneys may be
palpably enlarged and sometimes painful in patients with ARF, acute
pyelonephritis, renal cysts, amyloidosis or renal neoplasia. They may be
decreased in size and irregularly shaped in CRF. What appears to be renal pain
could also be pain referred from other abdominal organs or the spinal column or
the animal may just resent abdominal palpation and may not be experiencing pain.
Auscultation of the heart
and palpation of femoral pulses may indicate a cardiac arrhythmia or an abnormal
rate (fast or slow). Uremic myocarditis can cause an abnormal rhythm but occurs
uncommonly in dogs and cats. Hyperkalemia can result in bradycardia detectable
by auscultation or palpation of femoral pulses. ARF, bladder rupture or urethral
obstruction are the most common causes of hyperkalemia. Not all hyperkalemic
patients will be bradycardic. The presence or absence of bradycardia will
reflect the magnitude of hyperkalemia and the influence of factors which have an
opposite effect on heart rate. For example, if the animal is hypovolemic, the
physiologic response to hypovolemia is to increase heart rate and the
tachycardic response to hypovolemia may minimize the bradycardic effect of
hyperkalemia.
The urinary bladder
should be palpated for the presence of calculi or masses, and the wall thickness
and degree of distension and tone of the bladder muscle (detrusor) should be
assessed. Patient size, cooperation and the degree of bladder fullness will
determine whether the bladder and its contents can be palpated. When the bladder
is small, it retracts into the pelvic canal and cannot be palpated. The wall
thickness cannot be assessed when the bladder is full.
The external genitalia of
both sexes should be examined as genital tract disease may spread to the urinary
tract and vice versa. Check for the presence of discharges, masses, redness, or
pain. Because dogs and cats may compulsively groom themselves, discharge may not
be apparent on examination but often the owner will complain that the animal is
licking and grooming excessively or the genital region may be reddened
consistent with increased grooming.
Rectal palpation should
be performed in all male dogs to evaluate the prostate gland and pelvic urethra.
The pelvic urethra may also be evaluated by rectal palpation in female dogs. The
prostate should be evaluated for symmetry, size, shape, pain, and position. The
prostate is small or nonpalpable in normal, castrated dogs. It normally has a
bi-lobed shape with a longitudinal indentation on the dorsal surface. If the
prostate gland is small, it is located in the pelvic canal and can often be
palpated by rectal exam. As the gland enlarges it moves forward and falls over
the brim of the pelvis into the abdominal cavity. Push the caudal abdominal
contents in a caudal and upward direction to push the prostate back into the
pelvic canal which may allow you to feel it rectally with fingers of the
opposite hand.
Palpate all peripheral
lymph nodes (mandibular, prescapular, axillary and popliteal) and the perirectal
area, as lymphosarcoma and peri rectal tumors (and others) may produce
pseudohyperparathyroidism
with renal disease sometimes resulting from hypercalcemia.
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Laboratory
Evaluation
Hematology
WBC numbers will be
normal in most patients with urinary tract diseases but may be elevated in
patients with acute pyelonephritis, acute prostatitis or pyometra. Uremia
interferes with WBC function which may predispose renal failure patients to
infection which may result in leukocytosis.
A nonregenerative,
normochromic, normocytic anemia is often present in CRF and may also be present
in response to any chronic inflammatory or neoplastic process. A macrocytic,
hypochromic, regenerative anemia may be seen with blood loss; this progresses to
microcytic, hypochromic, nonregenerative anemia, if external blood loss is
chronic and leads to iron deficiency. Patients with CRF may have chronic
gastrointestinal bleeding from gastric ulcers. Patients experiencing acute
blood loss or hemolysis may not show signs of regeneration when they are first
evaluated. Acute blood loss can result in ARF mediated by
hypovolemia and ischemic renal injury. Hemolysis may result in ARF via
hemoglobin induced nephrotoxicity.
Platelet numbers are
normal in most patients with urinary tract disease but thrombocytopathia
characterized by decreased aggregation may lead to bleeding in renal failure
patients (acute or chronic). Platelet function can be evaluated by a buccal
mucosal bleeding time test and by clot retraction. Thrombocytopathia may
contribute to bleeding from gastric ulcers in uremic patients.
Total protein may be
increased due to dehydration (albumin) or due to chronic inflammation
(globulin). Total protein may be decreased in patients which are losing protein
in their urine (patients with glomerular disease). Total protein may also be
normal.
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Serum chemistries
Blood urea nitrogen (BUN)
is a product of protein catabolism and is increased in ARF, CRF, postrenal
azotemia, dehydration (prerenal azotemia), and after eating a high protein meal.
Gastrointestinal bleeding is comparable to ingesting a high protein meal and can
increase BUN.
Creatinine is produced
from muscle creatine at a constant rate and is not influenced by exogenous
factors such as diet. It is increased in ARF, CRF, dehydration (prerenal
azotemia), and post renal obstructions.
Phosphorus is increased
in ARF, CRF, and with skeletal growth (young animals) or bone destruction (osteolytic
states). Prerenal factors do not usually increase phosphorus.
Calcium is generally
normal or slightly decreased until renal failure becomes terminal, then serum
calcium may decrease. If calcium is increased, either it is the cause of the
renal failure (primary or pseudohyperparathyroidism) or the parathyroid glands
are functioning autonomously (tertiary
hyperparathyroidism). This occurs in some patients with chronic renal
failure and some young animals with congenital renal disease. Calcium is often
decreased (maybe markedly reduced) in patients with
ethylene glycol poisoning. Healthy young, growing dogs may have an elevated
calcium.
(link to hypercalcemic nephropathy)
Sodium serum levels are
generally normal, but may be increased or decreased reflecting the
type of dehydration (isotonic, hypotonic or hypertonic dehydration) or
previous fluid therapy.
Potassium will be
increased due to reduced elimination in oliguric ARF, post renal obstructions
and in patients with bladder rupture . Potassium may be normal or decreased
in CRF patients. Factors which will influence a patient's blood potassium
include urinary loss (greater loss in polyuric states), gi loss due to vomiting
or diarrhea and lack of intake in anorexic animals. Hypokalemic cats may
develop a myopathy characterized by painful muscles and increased CK. Cats
with hypokalemic myopathy are weak and may have difficulty holding up their head
(ventro flexion of the neck).
Serum albumin may be
decreased in proteinuric animals. Globulins are increased in animals
with chronic inflammation. Dehydration may increase albumin and can mask
hypoalbuminemia that may be observed when the animal is normally hydrated.
Bicarbonate is often
decreased in CRF and in ARF.
Blood pH may be reduced
in patients with ARF or CRF. Metabolic acidosis may develop in renal
failure due to impaired bicarbonate reabsorption, failure to excrete acid
breakdown products of metabolism, and reduced H+
secretion.
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Urinalysis
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The yellow liquid in that cup
IS worth its weight in gold!! A complete urinalysis can provide
information about the health of several organ systems including the urinary
tract. Attempt to collect a urine sample early in the course of evaluation
of your patients, before medications have been given. Several drugs (e.g.
glucocorticoids, fluids) or diagnostic agents (iodine-containing
radiographic contrast agents) can affect values in the urinalysis
complicating interpretation. |
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So, make it a routine practice to have receptionist staff inform clients
when they are making appointments, to not let their pet urinate for several
hours prior to the appointment as a urine sample may be collected. This
practice will also have a positive impact on the lawn and shrubs around the
practice:) |
The urinalysis should
always be interpreted in light of how the sample was collected. Collection
methods include free catch (midstream voided),
catheterization,
cystocentesis, or manual expression. The method by which you collect a urine
sample depends upon what information you intend to gain from the urine sample
and upon the degree of cooperation of the patient. If your goal is to assess the
animal's ability to concentrate urine, then any method of collection is
acceptable. If you are evaluating the patient for the presence of a urinary
tract infection, then cystocentesis is the preferred method of collection. If
the patient is straining to urinate and you wish to assess patency of the
urethra, then catheterization is the collection method of choice. Manual
expression can also be used to evaluate urethral patency and the diameter of the
animal's urine stream but is technically difficult in male dogs of any size and
large female dogs. Both manual expression and catheterization can cause gross or
microscopic hematuria.
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It will then become difficult to know if hematuria was caused by disease or
was iatrogenic. Cystocentesis will occasionally cause hematuria if a blood
vessel on the surface of the bladder was punctured by the needle. |
Catheterization is
technically difficult in female dogs and in awake cats of either sex.
Catherization is usually only performed in female dogs and in cats to assess
urethral patency or to instill contract agent into the bladder in the
performance of a contrast cystogram. Because it is technically difficult, even a
single catheterization of a female dog can lead to development of a urinary
tract infection.
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A urine sample can be collected off the floor or table top if the animal
voids before a more appropriate collection method can be performed. The
urine sample may contain unrecognizable debris from the collection surface.
If the floor or table top was cleaned with an antiseptic solution it is
possible to get false test results on some of the dipstip readings if the
urine sample is contaminated with the cleaning agent. Keep in mind these
limitations of an "off the floor" collection. |
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Analysis of a urine
sample. should be performed within 30 minutes of collection of urine. Delayed
analysis of the urine sample will allow any bacteria present in the sample to
proliferate (even a sample obtained by cystocentesis may contain a few bacteria
obtained from the skin surface). Bacterial numbers double every 45 minutes at
room temperature. As bacteria proliferate, the urine pH often
increases as the bacteria convert urea to ammonia. Formed elements in the urine
such as casts and cells may degrade in the "aged" sample and crystals may either
sediment out of solution or may dissolve providing a false representation of the
actual "in vivo" urine composition. Refrigeration at 5° C will preserve urine
for 2-3 hours by delaying bacterial growth. Refrigerated samples should be
warmed to room temperature before analyzing as some of the color pads on urine
dipsticks contain enzymes and the rate at which enzymatic reactions occur is
temperature dependent. Cold urine samples can lead to false negative readings.
False negative urine cultures may occur if urine is frozen or refrigerated for
12 to 24 hours or longer.
A complete urinalysis
should include color, turbidity, odor, specific gravity, pH, glucose, bilirubin,
occult blood, proteinuria, and sediment. The dipstick readings should be
obtained on either un centrifuged urine or supernatant, according to the
dipstick manufacturer's recommendations. The color pads on the dipsticks contain
enzymes. Enzymatic reactions are temperature dependent and enzymes are labile.
Bottles of dipsticks should be stored in a cool, dark location and expiration
dates on the bottles should be observed. Urine which has been refrigerated
should be warmed to room temperature before analyzing.
The sediment should be
prepared by centrifuging a standardized volume of urine, ~ 5-10 ml, at 2,000 RPM
for 5 minutes. The supernatant is decanted leaving about 1/2 ml in which the
sediment is resuspended. A drop of urine is placed on a microscope slide
and can be examined either stained or unstained. Casts and crystals are searched
for using low power (10x) and cells are observed with high power (40x). At least
10 fields should be examined using each magnification. The results are reported
as the range of formed elements observed in the fields counted. For example if 3
struvite crystals are observed in 2 fields, 1 crystal in each of 3 fields and
zero observed in the remaining fields, the result is reported as 0- 3 struvite
crystals per low power field (LPF).
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The color of normal urine is due to urochromes derived from hemoglobin
breakdown.
- Gold or orange
urine may indicate extreme concentration, increased amounts of bilirubin
or the elimination of sulfa drugs.
- Green
- Red urine is due
to red blood cells, free hemoglobin, myoglobin or dyes from drugs such
as adriamycin (a chemotherapeutic agent)
- Blue urine may be
seen in animals treated with methylene blue
- Clear urine
indicates extreme dilution
- White, cloudy
urine indicates an increase in a formed element such as WBC, bacteria or
yeast, RBC, sperm, crystals, and epithelial cells. The cause of
turbidity is best explained by sediment exam.
|
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The odor of normal urine is due to volatile fatty acids, not due to ammonia.
Freshly voided urine which has an ammonical smell is suggestive of the
presence of a urinary tract infection. If the urine sample is "aged" for
several hours, bacterial degradation of urea to ammonia in a "normal" urine
sample will result in the odor of ammonia. |
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The specific gravity or
osmolality is used to assess the ability of the renal tubules to concentrate or
dilute. The significance of other components of the urinalysis should be
interpreted in association with specific gravity or osmolality as they provide
information regarding the ratio of solute to water.
Osmolality is a
colligative property and is dependent on the number of particles per unit volume
of solvent (fluid). It is independent of the chemical nature, size and molecular
weight or charge of the solute (particles). Normal osmolalities range between
50 mOsm-2400 mOsm/Kg in the dog. Because practices do not usually have an
osmometer, urine osmolality is not often measured.
Specific gravity is the
ratio of the weight of urine to the weight of an equal volume of water. It
depends on the number of molecules plus molecular size and weight and therefore,
the relationship between osmolality and specific gravity is only approximate.
Specific gravity is measured with a refractometer.
A single urine specific
gravity value can fall anywhere in the normal range, including the isosthenuric
range and may still be normal for that animal. Specific gravity constantly in
the isosthenuric range (1.007-1.017) demonstrates no work is being done by the
tubules on the glomerular filtrate and suggests intrinsic renal disease. 2/3 of
the nephron mass of both kidneys must be destroyed before the kidney loses
its ability to concentrate and dilute urine resulting in a persistent
isosthenuric specific gravity. Azotemia and dehydration with an isosthenuric
specific gravity suggest intrinsic renal disease. There are many nonrenal
diseases that cause urine to be in the isosthenuric range.
(evaluation of patients with dilute urine)
Categories of
Urine Concentrating Abilities (approximate USG values)
| Hyposthenuria |
<1.007 |
| Isosthenuria |
1.007-1.017 |
| Minimally Concentrated |
1.018- 1.030 |
| Hyperstenuria |
>1.030 (dog) >1.035 (cat) |
Large amounts of protein
or glucose can lead to the impression of better concentrating ability than is
actually present, although the magnitude of impact on urine specific gravity is
usually not large. 0. 4g protein/100 ml and 0.27 g glucose/100 ml will raise
urine specific gravity 0.001 (a 1.018 specific gravity with 4+ glucosuria is
really 1.010).
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Measurement of urine pH
may provide a rough assessment of the patient's acid-base status and the ability
of the kidneys to regulate acid base balance. Urine pH should be interpreted in
light of other clinical findings. The normal range is variable but usually
5.5-7.5.
Causes of alkaline urine
include:
- diets rich in
vegetable products,
- postprandial gastric
secretion of HCL
- bacterial catabolism
of urea to ammonia (UTI or old urine)
- administration of
alkalinizing drugs (e.g. bicarbonate)
- metabolic alkalosis.
Cause of acid urine
include:
- diets rich in animal
origin products
- administration of
acidifying agents (e.g. methionine)
- metabolic acidosis
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Glucosuria occurs when
hyperglycemia exceeds the renal threshold (approximately 180 mg%) for
reabsorption of glucose.
- diabetes mellitus
- hyperadrenocorticism
(rare)
- acute pancreatitis
(hypoinsulinism)
- pheochromocytomas
- iatrogenic (parenteral
glucose therapy, steroid administration (rare), or epinephrine
administration)
Glucosuria without
hyperglycemia may occur
- in animals with
primary renal glucosuria (Fanconi syndrome)
- some congenital renal
diseases
- acute tubular
dysfunction in acute renal failure
- can be normal in pups
and kittens < 8 weeks old
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Bilirubin should be
interpreted in conjunction with urine specific gravity. 10-20% of normal dogs
have a small amount (trace to +1) of bilirubin in the urine. Male dogs have a
lower threshold for loss of bilirubin in the urine compared to female dogs.
Any amount of bilirubin in the urine of a cat is abnormal. Bilirubinuria is
indicative of:
- hemolysis
- hepatopathy
- biliary disease
A positive dipstick
reading for blood indicates the presence of intact RBC (hematuria), or the
presence of free hemoglobin (hemoglobinuria) or myoglobin (myoglobinuria).
Dipsticks from different manufacturers may have different degrees of sensitivity
to hemoglobin within cells versus free hemoglobin and some may have different
color pads for free hemoglobin versus hemoglobin within cells.
If due to intact RBC, the
supernatant will be clear following centrifugation as the RBC will pack into the
sediment. If due to free hemoglobin or myoglobin, the supernatant will remain
red after centrifugation. Hemoglobinuria is usually accompanied by red plasma
and a low PCV. Myoglobinuria may result in red plasma although myoglobin is not
bound to a plasma globulin as is hemoglobin so it is cleared from the plasma
faster than hemoglobin. Hemoglobinuria is usually due to intravascular hemolysis
and is much more common than myoglobinuria in dogs and cats.
If the urine contains
free hemoglobin but the plasma is clear and the PCV is normal, then the red
color is due to RBC that originated in the urinary tract and hemolysis occurred
either while the urine was in the bladder or after voiding. RBCs in urine with a
low urine specific gravity may lyse releasing free hemoglobin. You may see
fragments of RBCs called ghost cells in the urine sediment.
Proteinuria is presented in depth in another section of notes.
The significance of urine
sediment must be interpreted with knowledge of whether the sample was
catheterized, free catch, cystocentesis or expressed. Hematuria-indicates
hemorrhage, caused by inflammation, calculi, bleeding disorders (most likely
associated with low platelet numbers or abnormal platelet function), parasites,
estrus, prostatic disease, palpation or catheterization, necrosis, trauma, or
neoplasia anywhere along the urogenital tract. Hematuria may be grossly visible
or microscopic.
Pyuria (large numbers of
WBC in urine) indicates infection or inflammation anywhere along the urogenital
tract. Greater than 3 to 5 WBC/HPF in a cystocentesis sample or greater than 5
to 10 WBC/HPF in a voided or catheterized sample is considered significant
pyuria.
Leukocyte
esterase tests for WBC and nitrate tests for bacteria are not reliable
in dogs and cats.
Applicability of leukocyte esterase test strip in detection of
canine pyuria.
"A
commercially available leukocyte esterase assay was evaluated for
application in analyzing canine urine for the detection of pyuria.
In 229 urine samples, the leukocyte esterase activity was compared
with leukocyte concentrations, as assessed by microscopic sediment
analysis and chamber cell counts. The leukocyte esterase assay was
specific (93.2%) for canine pyuria, but was poorly sensitive (46.0%)
and did not appear to be applicable to analysis of canine urine
samples."
Casts
can be composed of Tamm-Horsfall mucoproteins and some plasma protein and their
shape is molded by tubular lumen.
Casts contain material in
their matrix that was present in the tubule when the cast was formed. Hyaline is
pink and homogenous. Epithelial cells are usually desquamated tubular epithelial
cells. RBC from hemorrhage into renal tubule. WBC from inflammation of renal
tubules. Any cast can be pigmented with large amounts of bilirubin in the urine.
Large numbers of casts indicate active disease. A few casts may not be
significant, especially if not found on repeated sediment exams.
Spermatozoa are normally
found in male urine even if the sample is collected by cystocentesis. They can
also be found in female urine post breeding.
Urethra has bacterial
flora so voided bacteriuria may not be significant. Bacteria in urine analyzed a
long time after collection may not be significant. Bacteria in a sample obtained
by cystocentesis are always significant.
Lipiduria may be due to
contaminants such as catheter lubricants. It may occur as a result of
degenerative changes in tubular epithelium. This may be the cause of lipiduria
in dogs with nephrotic syndrome. It may be normal in cats as renal epithelial
cells contain a lot of lipid.
Crystal type depends on
urine pH, solubility, and concentration. Crystals seen in alkaline urine include
triple phosphate, amorphous phosphates, calcium carbonate, and ammonium urate.
Crystals seen in acid urine include uric acid, cystine, calcium oxalate, and
hippuric acid. Crystals of diagnostic value include cystine crystals in
cystinuria and oxalate crystals in ethylene glycol poisoning.
Urinalysis
by Dr. Joe Spano at Auburn
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Renal function tests help determine the location and
extent of renal functional impairment. Function tests may be abnormal earlier in
the disease process than individual laboratory values like BUN, creatinine, or
phosphorus. Renal function tests do not indicate specific cause, acuteness or
chronicity, or degree of reversibility or irreversibility. Renal function tests
should be re-evaluated at intervals to establish the trend of abnormal renal
function and to prognosticate and evaluate response to therapy.
Urine specific gravity
(USG of water is 1.000) is the relative amount of solute and solvent in a
solution. Most normal dogs will have a USG >1.030 and cats >1.035 in the
cat, although any USG can be "normal" in an individual animal. When >2/3 of the nephrons have been destroyed there is impaired ability to
dilute and concentrate. Isosthenuria (1.007-1.017) in the face of dehydration or
azotemia is indicative of renal damage.
Osmolality
measures number of osmotically active molecules in solution. A urine/plasma
osmolality >1 indicates ability to concentrate. The ratio is 7 or > in normal
dogs.
A
water deprivation test
is performed by with holding water to stimulate
the release of endogenous ADH from the posterior pituitary gland. ADH enhances
water reabsorption in the distal convoluted tubules and collecting ducts by
increasing the permeability of the tubules. Failure to concentrate urine
following water deprivation implies the presence of renal disease (tubules
handling an increased solute load with obligatory polyuria), diabetes insipidus
(failure to release ADH), nephrogenic diabetes insipidus (tubules not responsive
to ADH), and/or medullary washout. Contraindications for water deprivation
include azotemia and/or uremia and clinical dehydration.
Excretory urography
(EU, IVP) provides a crude qualitative evaluation of renal function. Poor renal
concentrating ability may produce a poor contrast density.
Determination of glomerular filtration rate (GFR) (clearance tests): Clearance denotes the
amount of plasma that is completely cleared of a substance per unit time. The
amount of a substance excreted in the urine is equal to the amount filtered by
the glomeruli plus the net transfer of that substance by tubular reabsorption or
tubular secretion. Amount excreted = amount filtered + amount secreted - amount
reabsorbed. If a substance is freely filtered but neither secreted or
reabsorbed, the amount excreted per unit time is equal to the amount filtered
per unit time. A polysaccharide inulin meets the criteria of being freely
filtered and not secreted or reabsorbed by the tubules. The clearance of inulin
is equal to GFR. As inulin is not a substance endogenous to the body it must be
infused to maintain a constant plasma level which is not practical to perform
except in research labs. Creatinine is an endogenous substance formed at a
fairly constant rate from muscle creatine. Creatinine clearance overestimates
GFR in male dogs due to some proximal tubular secretion.
Another substance
used to calculate clearance is iohexol, an iodinated radiographic
contrast agent, can be used to estimate GFR but is only available at
some referral centers.
Relationship between plasma iohexol clearance and urinary exogenous
creatinine clearance in dogs
Likewise methods
that use radioisotopes to measure clearance are available at some
referral centers.
The procedure to
perform creatinine clearance:
Empty the bladder,
discard urine, and note the time. Collect and save all urine produced
for the next 12-24 hours or longer, including the final urine sample.
Urine can be collected by catheterization, free catch of all voided
urine, or collected in a metabolic cage.
The actual time is
not critical as long as the times the test begins and terminates are
recorded. The longer the time of collection period the more accurate the
results.
At the midpoint of
collection period, collect a serum sample for creatinine determination. In
actual practice, a sample at the beginning or end of urine collection period
is acceptable. Measure total urine volume and determine urine creatinine
concentration
Compute clearance:
U = urine creatinine
V = urine volume/time of collection
S = serum creatinine
Example:
calculation of creatinine clearance
10 kg (20 lb) male
beagle produces 1,400 ml urine in 24 hours
Serum creatinine 1
mg/dl (S)
Urine creatinine 10 mg/dl (U)
1440/24 hours = 1 ml/min (V)
| U x V = |
10 x 1 = |
10 ml/min |
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10 ml/min |
= 1.0 ml/min/kg |
|
S |
1 |
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10 kg |
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Normal is 2-4
ml/min/Kg.
The creatinine
clearance can be decreased by prerenal or renal causes. If no prerenal
causes can be identified, the creatinine clearance can be crudely
interpreted as the percent renal function remaining. i.e. If normal is 2-4,
a patient with a clearance of 0.3 ml/min/Kg has approximately 10% renal
function (0.3/3).
If the patient is
proteinuric, can quantitate actual protein loss with same 24 hour collection
of urine.
Exogenous
creatinine clearance (see AAHA, vol 18, 1982, p 804) is comparable to
inulin clearance. A subcutaneous administration of creatinine shows up in a
20 minute urine collection period.
Radioisotope
clearance studies (requires special facilities to handle to isotope) does
not require urine collection and happens over a short time period.
Measurement of PTH values should be obtained from a lab with validated
assays for the dog and cat. Elevated PTH values occur in CRF and primary
hyperparathyroidism.
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Radiography of the urinary tract
Reference:
Uro-radiology by Dr. Jeryl C. Jones, Virginia-Maryland Regional
College of Veterinary Medicine.
Survey radiographs can
illustrate kidney size and contour
Cat 2.4 - 3.0 times the
length of L2
Dog 2.5 - 3.5 times the length of L2
Radiopaque calculi can be
visualized on survey radiographs. Calculi may be located in the renal pelvis,
bladder or urethra. If the bladder contains urine, its size, shape and position
can be determined on survey radiographs.
Contrast studies can be
performed to examine the kidneys, ureters, bladder or urethra.
- the contrast study
used to image the kidneys and urethra is an intravenous pyelogram (IVP) also
called an excretory urogram EU. Positive, iodine containing contrast is
administered IV. IVP's should not be performed in proteinuric patients as
the contrast material may precipitate protein in the renal parenchyma and
lead to impaired renal function.
- the contrast study
used to image the bladder is a cystogram. Cystograms may be performed using
air (negative contrast), an iodinated contrast agent (positive contrast) or
a combination of negative and positive contrast agents. Abnormalities which
may be observed include: radio-lucent calculi, thickness of the bladder
wall, and masses in the lumen of the bladder
- The urethra is
evaluated using a positive contrast urethrogram. Contrast can be expressed
from the bladder into the urethra in a normograde direction or the contrast
can be injected into the distal end of the urethra using a catheter; a
retrograde urethrogram.
Iodinated contrast agents
influence urine specific gravity; the USG may be falsely increased or decreased
by the contrast agent. Contrast agent may also impair bacterial growth so
samples for urine culture should be obtained before performing contrast studies.
Ultrasound examination of
the urinary and genital tracts can provide useful information but interpretation
is dependant upon the skill and experience of the ultrasonographer. Information
that can be obtained from ultrasound examination includes:
- kidney size and shape,
renal calculi, size of the renal pelvis, cysts or masses within the kidneys
- bladder wall integrity
and thickness, intraluminal masses, calculi, cellular debris in bladder
- urethral calculi
- prostatic size, shape
and architecture
- uterine size and
contents including diagnosis of pregnancy and pyometra
Ultrasound can be used to
guide aspiration or biopsy of organs and structures.
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Renal biopsy
can be obtained using a specialized needle, percutaneously, either "blindly" or
using ultrasound guidance or a wedge biopsy can be obtained via laparotomy. A
more recently described technique is the use of laparoscopy to obtain a kidney
biopsy. Biopsy may be indicated in:
- ARF patients who are
not responding to treatment in order to determine prognosis
- patients with enlarged
kidneys
- proteinuric patients
to obtain a morphologic diagnosis, to better prognosticate (reversible or
irreversible), and possibly to choose appropriate therapy
- young patients with
suspected familial renal disease in order to determine if the disease is
consistent with congenital renal disease
Biopsies are not
contraindicated in CRF patients but the information one stands to gain by the
biopsy is minimal. The end result of most types of renal insults is similar and
not reversible.
Biopsies are more likely
to be diagnostic in generalized rather than focal disease. Contraindications to
biopsy include hemorrhagic tendencies, renal abscesses, and advanced
hydronephrosis or pyelonephritis. Any azotemic patient may have an abnormal
ability to clot so the patient must be observed for post biopsy bleeding.
The currently
recommended needle is a disposable spring-loaded biopsy needle (E-Z Core
Single action Biopsy Device: Products Group International, Lyons CO.)
This needle is favored over the older Tru Cut Needle.
Diagnostic quality of percutaneous kidney biopsy specimens obtained
with laparoscopy versus ultrasound guidance in dogs.
"CONCLUSIONS
AND CLINICAL RELEVANCE: Results suggest that excellent-quality renal
biopsy specimens with large numbers of glomeruli can be obtained
with 14-gauge, double-spring-activated biopsy needles during
laparoscopy. Renal biopsy specimens obtained with 18-gauge biopsy
needles frequently had few glomeruli and often were crushed or
fragmented, increasing the difficulty in making an accurate
diagnosis."
Last Edited: Jul 26, 2007 2:18 PM
