In a recent local meeting, a fellow veterinarian said 20 years ago a lot more simple things entered the veterinary practice
door. Today, the majority of the dogs and cats entering the veterinary practice are sick and require immediate point-of-care.
Is your veterinary practice moving toward greater point-of-care capabilities?
To provide clients with the highest quality of care for their pets, veterinarians should make regular diagnostic testing a
mainstay in their practices, especially for aging pets that can have notable medical changes in just a few months.
Immediate point-of-care starts with the mainstays of any veterinary practice - hence, collection of accurate case history
followed by performing a thorough physical examination. Thereafter, samples are collected for performing a CBC, serum chemistry
profile and urinalysis. Results obtained from the case history, physical examination and laboratory tests (CBC, serum chemistry
profile, and urinalysis) are then used to determine additional diagnostic needs. There are several common practical errors
associated with regular diagnostic testing that occur in most veterinary practices (Table 1). For example, a common practical
error is performing radiography and/or ultrasonography before the case results of the CBC, serum chemistry profile, and urinalysis
Effects of biological factors
Many biological factors, such as breed, age, gender and body condition score, influence the results of serum chemistry profile
tests. Young dogs and cats tend to have a lower PCV, BUN and serum total protein value and a higher serum ALP, total bilirubin
and phosphorus value than established as the normal range. Similarly, older healthy dogs and cats tend to have decreases in
the BUN, serum GGT, and serum creatinine value and increases in serum total protein and potassium value. Other biological
factors involve those that can be controlled when drawing the blood sample, such as ensuring the animal is properly fasted.
Non-biological factors are those related to sample collection and handling, such as choice of anticoagulant used and UV-light
Table 1: Practical Errors Commonly Made in Regular Diagnostic Testing
More veterinary practices today use in-house automated chemistry analyzers or send samples daily to commercial veterinary
reference laboratories. In-house testing provides results more quickly and at more flexible times than if tests are performed
at commercial veterinary reference laboratories. Estimates of the percentage of samples collected in veterinary practice that
are compromised by the presence of hemolysis, lipemia, icterus, or other substances such as medications ranges from 50 percent
to 80 percent. The impact of these interferences on serum chemistry profile results depends, in part, on the analyzer and
methods used. The specific impact on a serum chemistry test result will differ depending on the type of instrumentation.
High body condition scores
Obese cats (i.e., high body condition scores) tend to have a higher than normal hematocrit. The serum concentrations of cholesterol
and triglycerides are significantly increased in obese cats and dogs. It is interesting that fasted serum glucose concentrations
are not usually increased in the obese cat or dog. As cats become obese, serum free thyroxine (FT4) by dialysis increases
in the normal range and correlates with most indices of obesity, whereas serum total thyroxine (TT4) and total triiodothyronine
(TT3) concentrations do not change significantly.
Liver and gall bladder evaluation
The common serum chemistry profile tests for liver and gall bladder disease include the serum leakage enzyme tests (ALT and
AST) and the cholestatic tests (ALP and GGT). Other tests for liver function include serum total bilirubin, bile acids, albumin,
globulin and cholesterol. Following liver parenchymal injury, serum ALT increases followed by serum AST. Serum AST returns
to normal more rapidly than serum ALT provided there is no added muscle tissue damage. Chronic liver disease is likely if
serum ALT and AST both remain increased. Cholestasis can result from impaired bile flow or can be drug-induced (increased
glucocorticoid concentration and administration of anticonvulsants). Serum ALP and GGT are normally present in low concentrations.
Impaired bile flow stimulates production of ALP and may also be linked to retention of bile acids.
Bile acids are stored in the gall bladder and then released into the intestinal tract. Most bile acids are actively resorbed
in the ileum and carried to the liver where they are re-conjugated and excreted as part of the enterohepatic circulation of
bile acids. When functional hepatic mass is reduced extraction of bile acids from blood is affected. Measurement of serum
bile acid concentrations is, therefore, a good indicator of hepatobiliary function. Increased serum bile acid concentrations,
however, are not specific for the type of underlying liver disease. Other factors independent of hepatobiliary function that
may affect serum bile acid concentrations are decreased gastrointestinal transit time and spontaneous gall bladder contraction.
Prolonged fasting, intestinal malabsorption, or increased intestinal transit time through the intestine (e.g. diarrhea) can
lower serum bile acid concentrations.
Practical errors are commonly made when diagnostic testing is done. It is important to train staff to avoid making these errors
which could have an impact on an accurate diagnosis.
Nearly all blood constituents pass through the renal glomeruli and enter the tubules. Kidney injury may result in an inability
of the glomerulus to retain cells and proteins or impair the resorptive capability of the tubules. Azotemia (i.e., increased
BUN and serum creatinine) occurs when any condition alters the glomerular filtration rate or when the urinary tract is obstructed.
Nutritional status and gastrointestinal hemorrhage will also affect BUN concentrations. Because creatinine is formed during
normal muscle metabolism, the amount of creatinine present is affected by the animal's total muscle mass. An alteration in
the ratio of the BUN-to-creatinine concentrations is a more significant indicator of renal disease than individual measurements
of either component. If in question about actual renal function for the older dog or cat, an iohexol clearance test that measures
glomerular filtration rate may also be used.