Veterinary laboratory tests, part 1

Our pets and farm animals get checked by the vet every once in a while. Often the vet needs a sample to test. For us owners the samples are usually classified by the substance needed: there are blood test, tests from urine samples, test from stool samples etc. It's easy to understand and definitely clear enough for everyone involved.

Veterinarians and laboratories, however, use a bit different kind of classification. For their purposes it provides more clarity. Some common types of tests are 

• Hematology
• Chemistry
• Urinalysis
• Cytology and histology

Tests are often run in "panels", meaning a group of tests which are often requested together. Instead of separately requesting for a test for all liver-related values, for example, the vet can just order a "liver panel". The panels available differ per laboratory and testing company.  

Hematology

Hematology tests the different cells in the blood. It studies the life cycle, form and size (morphological features) and the amounts of these cells.  The blood to be sampled is submitted either in a test tube or as a smear on a glass. The sample should be as fresh as possible to avoid lysis (cells breaking down) and clotting. If the sample is shipped to an external laboratory correct packaging and shipping are vital to preserve the sample in good quality. 

The tests are further classified by what cells are being studied. Red blood cells, white blood cells and platelets all have their own functions in the body. For red blood cells we can for example test for hematocrit (HCT), which is calculated from the amount of red blood cells and the mean cell volume. We can also calculate reticulocyte percentage to see how much of the red blood cells are immature. A high number of immature cells could indicate blood loss by bleeding or cell death. 

For white blood cells we calculate the total number, morphology and percentage of different types of white blood cells. The changes in these cells form a leukogram. 

Platelets help the blood clot, and are the third type of cells used in hematological tests. Similarly to red and white cells, we count the number and percentage of platelets. We can also determine their morphology. Too many platelets is called thrombocytosis (increased clotting risk), and not enough platelets is called thrombocytopenia (blood is not clotting properly). 

Chemistry

Chemistry tests urine or blood, but in a different way than hematology. These tests can be called clinical chemisty, clinical pathology of blood chemistry. Unlike hematology, chemistry is tested most often from serum or plasma. Serum and plasma are acquired by removing the cells from the blood sample. If the blood is left to clot,  serum remains. If the clotting is prevented with anticoagulant, the result is plasma. 

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Some examples of chemistry tests are electrolytes, minerals and kidney function.

Electrolytes help cells to function properly. They are carefully regulated, and any deviations can point to a health concern. Sodium concentration can be measured to estimate the the amount of fluids in the body (dehydration). Potassium is crucial to the correct working of muscles. Minerals like calcium and magnesium can reveal organ failure (the body will get lacking minerals from internal organs) or muscle weakness due to lack of calcium (milk fever in cows being a well-known example).   

To estimate kidney function a chemistry test measuring creatinine or urea nitrogen can be done. 

Urinalysis

Urinalysis is the analysis of urine. It focuses on describing the urine (color, cloudiness) and looking at the bacteria and biochemical properties (such as protein, blood and pH). All of these values describe the functioning of the kidneys and urinary tract. 

Much of basic urinalysis can be done at a clinic using a simple dipstick. It's a stick with several pads, which is dipped into the urine. Each pad reacts to a specific substance in the urine. Looking at the colors of the pads the nurse or vet can determine the basic properties of urine.