Download GETTING THE MOST OUT OF THE MINIMUM DATABASE

GETTING THE MOST OUT OF THE MINIMUM DATABASE: THE COMPLETE URINALYSIS
Dennis B. DeNicola, DVM, PhD, DACVP
IDEXX Laboratories, Inc.
Westbrook, Maine, USA
BACKGROUND
Many people fail to perform a complete urinalysis associated with their minimum database, which can be quite
problematic when trying to interpret hematology or biochemical abnormalities. The urinalysis should be
considered the third leg of a three-legged stool; if any of the three legs (urinalysis, complete blood count and
biochemistry profile) are missing, the stool cannot stand. The information in the urinalysis is essentially to
properly assess both the complete blood count (CBC) and biochemical profile. When assessing the minimum
database, performing the analysis in an organized and standardized manner will minimize the potential for
missing critical diagnostic information. My personal recommendation is to first look at the CBC and urinalysis
findings first and then the electrolyte / acid-base profile of the biochemical profile before evaluating the whole
biochemical profile. The CBC and urinalysis in particular provide insight into the general overall condition of the
animal; identification of significant anemia, inflammatory disease, glycosuria, ketonuria or even alkaline urine
sets the stage to help characterize the severity and potential systemic nature of the underlying disease
process. The biochemical profile provides more specific direction as to which organ system(s) are involved. In
addition, the word “complete” is critical when speaking about the urinalysis. There are three components to the
urinalysis and they include the physical, chemical and microscopic examination. Performing only a specific
gravity measurement or just a dry-chemistry reagent strip test does not make a urinalysis. All three are
needed. Rarely will just the urinalysis provide tremendous insight into underlying disease, but it is critical for
interpreting other laboratory data.
URINALYSIS: COMPONENTS AND VALUE
Many of the components of the physical, chemical and microscopic portions
of the urinalysis provide valuable and in some cases, essential, information to
allow correct interpretation of CBC and Biochemical Profile results. In
selected cases of liver disease, changes in the urinalysis such as finding
hyperbilirubinuria may be seen prior to biochemical profile changes.
Remember that the complete urinalysis can provide information about many
systemic disease processes, not just diseases associated with the urinary
system. The major components of the urinalysis and their relative value for
interpreting other data are indicated below.
Although the physical examination of the urine is relatively simple and clearly cost-effective, it provides
significant information for interpretation of the rest of the urinalysis. Simple identification of a turbid urine
sample in the dog or cat is highly suggestive of increased cellularity (leukocytes and bacteria); however, in the
horse or rabbit, it may merely be associated with mucus in the specimen. It clearly identifies the essential need
for microscopic evaluation. The urine specific gravity is merely a physical property based on refractometry,
which is the most common method for estimation in veterinary medicine. Without the urine specific gravity,
mild to moderate increases in creatinine and BUN are impossible.
Physical Examination Component Interpretative value Color Erythrogram Turbidity Leukogram Specific gravity Creatinine, BUN The chemical examination of the urine provides insight into how the biochemical profile is interpreted, whether
it is associated with work-up of a case of hypoalbuminemia or simple interpretation of a case of suspected
cholestasis. The simple evaluation of urine pH can many times provide insight into systemic acid-base
abnormalities even before the biochemical profile is evaluated. Also characterizing the presence of diabetic
ketoacidosis is impossible without the urinalysis.
Component pH Protein Ketones Bilirubin Urobilinogen Blood Chemical Examination Interpretative value Renal, Acid-­‐base Renal, Pre-­‐renal, Post-­‐renal Diabetes Hepatic, Erythrogram Hepatic Urinary, Erythrogram, Muscle The microscopic evaluation of the urine is clearly one of the most problematic portions of the complete
urinalysis in that many individuals are not comfortable or competent in identifying various formed elements of
the urine. Practice is required and the evaluation of the unstained urine specimen is recommended to avoid
various artifacts associated with staining from interfering in the analysis. Both cellular and crystal evaluation
can provide valuable information not attainable with just the use of the other two elements of the minimum
database, the CBC and Biochemical Profile.
Microscopic Examination -­‐ Cells Component Interpretative value White blood cells Urogenital Red blood cells Urogenital Epithelial cells Urogenital Bacteria Urogenital Fungi Urogenital Microscopic Examination -­‐ Crystals Component Interpretative value Struvite Urinary Bilirubin Hepatic Ca carbonate Normal Amorphous Non-­‐specific Ca oxalate dihydrate Non-­‐specific Ca oxalate monohydrate Ethylene glycol toxicity Ammonium biurate Hepatic Cystine Urinary Drug -­‐ associated Drug therapy Within the microscopic portion of the urinalysis identifying specific formed elements, particularly leukocytes and
bacteria which are common occurrences in veterinary medicine samples, is challenging. Regardless what is
done in the veterinary clinic, practice is clearly critical to becoming proficient in urine microscopy. Currently
there are several automated microscopy systems for human urine sediment evaluation and in the near future
similar technology will be available in veterinary medicine. Itemized below are several points to consider as
aids for making a seemingly difficult process a little simpler.
1.
Follow a standardized process for preparing the microscopic specimen to help provide some
consistency in your analysis. There are many different ways described in the literature and textbooks
regarding both the actual centrifugation process and the volume of urine used for making the
preparation. Various centrifuges can and are used in veterinary practices. The key feature of the
centrifuge is to assure that a gravitational force of 400-450 g should be used. Theoretically, this allows
as gentle concentration of the various formed elements found in the urine to assure their presence
when the sample is examined microscopically. Since different sized centrifuges and different
centrifuge speeds are possible, you should consult the manufacturer of your particular centrifuge to
assure the correct settings. Some centrifuges actually provide a “urine” specific setting for proper
processing.
2.
Assure that your microscope is properly set. Unlike typical brightfield microscopy that we use for blood
film and cytology specimen evaluation, we need to actually decrease the light intensity and after the
focus of the light source for urine specimens. There is no one particular setting and each microscope
type has its own unique features, but basically, we decrease the light intensity and adjust the iris
associated with the condenser below the microscope slide stage and potentially the actual height of
the condenser itself. In bright field microscopy, the iris is typically wide open and the condenser is in
almost its highest position (directly below the stage where the slides are placed). While examining a
urine sediment specimen, make the adjustments just suggested until you find a position that makes the
formed elements slightly refractile, which will optimize your chances of actually finding the various
elements including cells, bacteria, casts and crystals.
3.
Learn how to perform your microscopic evaluation with unstained preparations if possible. Most
people feel more comfortable with something that is stained, but stains often times introduce various
artifacts that can interfere with accurate assessment. With a little practice, you will find that examining
the unstained preparation will become quite simple. There are times where we need to look at a
stained preparation and in this case, the best thing to do is to make a dried cytologic preparation with
the concentrated urine similar to what you normally do for any other body fluid. Then stain this
specimen with a stain you are familiar and comfortable with, which for the vast majority of us, is the
stain we use for blood films and cytologic preparations. The most common times we revert to a
stained dried cytologic preparation is when we need to confirm the presence of bacteria or we want to
better characterize cell morphology as would be needed when investigating for possible transitional
cell carcinoma in the urinary tract.
Some examples of common occurring formed elements found in our veterinary samples are included below:
Erythrocytes
Erythrocytes (red arrows) and leukocytes (blue arrows)
Leukocytes and erythrocytes
Nonsquamous (transitional) epithelial cells and
erythrocytes
Squamous epithelial cells
Transitional cell carcinoma
Transitional cell carcinoma
Leukocytes, erythrocytes and rod-shaped bacteria
Hyaline casts
Granular casts
Waxy and granular cast
Calcium oxalate dihydrate crystals
Calcium oxalate monohydrate crystals
Struvite crystals
Ammonium biurate crystals
Bilirubin crystals
Calcium carbonate crystals
Cystine crystals
Uric acid crystals
Amorphous phosphate crystals
Lipid droplets