Laboratory tests are used by vets to help them diagnose disease in animals that are ill. Increasingly, they are also used as part of a routine health check to detect hidden disease before the development of obvious symptoms. This allows your dog to be treated earlier and more effectively. A very important use is to test that your dog’s kidneys and liver are working properly before a surgical operation.
Who carries out the test?
Many veterinary practices have their own small laboratory where a limited range of tests can be carried out. Results are obtained quickly which allows rapid decisions on treatment. Often a quick test is carried out in the practice and a sample is then sent to the commercial laboratory to check that the results tally.
If a broader range of tests is required, samples will be sent to a commercial laboratory which will usually send results of routine tests back to your vet by fax, telephone or e-mail within 24 hours (although some tests may take 10 days or longer to complete). Commercial laboratories are able to advise your vet on how to interpret difficult test results. Occasionally, especially if samples are delayed in the post, they may deteriorate and your vet may need to repeat the test.
What is being tested and why?
There are a whole battery of tests which can be done on different types of samples, although not all are used to investigate every disease. Some samples are more easy to obtain than others and the effects that testing has on your dog will vary.
These are the most commonly performed laboratory tests because suitable samples are usually easy to get. It is possible to tell a great deal about your dog’s health or disease from the concentration of different chemicals in the blood. The proportion of different types of blood cells and the presence of proteins called antibodies (which are produced as part of the body’s defence against disease), may tell your vet how well your pet is fighting the disease.
Samples are usually taken from a vein in the leg or neck using a hypodermic needle and syringe. A patch of fur over the vein is shaved and the skin disinfected with surgical alcohol to clean the skin and allow your vet to see the vein more easily. A few millilitres (about a teaspoon) of blood are put into special containers to prevent it clotting.
Blood sampling is not painful although some animals don’t like being held whilst the sample is taken. Some bruising may occur if your dog has delicate skin or struggles when the sample is being taken. The puncture hole will heal quickly unless your dog has a disorder that prevents the blood clotting.
Blood tests can show if your dog is anaemic or show whether its liver and kidneys are working properly.
These are carried out to check for diseases such as diabetes or cystitis. Urine can be checked to see if it contains proteins, sugar or signs of infection.
Urine samples can be collected by catching a few drops of urine in a thoroughly cleaned container under your dog as it empties its bladder. The sample should be kept in a sealed bottle inside a refrigerator and tested as soon as possible.
When it is not possible to wait for a naturally produced urine sample, your vet may collect one using a catheter (a special tube), passed directly into the bladder through the urethra, or using a needle inserted into the bladder through the skin over the belly. It might be possible to collect samples in this way without sedating your dog and these techniques are no more complicated or dangerous than taking a blood sample.
Small samples of faeces often help to identify diseases of the digestive system. The sample may be tested to see if any unusual bacteria are growing that indicate an infection in the intestines. Further tests may be carried out to see if your dog is unable to digest certain foods or if its faeces contain eggs from parasitic worms.
A dog’s eyes, ears and nose or skin can often become infected with disease-causing bacteria, viruses or fungi. Swabs are taken by gently rubbing the affected area with a small piece of cotton wool. The swab is then either transferred onto a glass slide for examination under a microscope or cultured and tested to see if bacteria can be grown. The results of a culture test may take a few weeks or longer, (in the case of some slow growing bugs).
Dogs with skin disease will be tested to see if they are infected with parasitic mites. The skin is scraped gently with the edge of a scalpel blade until bleeding occurs. This may cause minor discomfort to some dogs although others tolerate it fairly well. There are usually only small numbers of mites and a large number of scrapings may have to be taken from several areas before finding them. The skin sample is transferred onto a glass slide and examined under a microsope.
If a dog has a growth on its body it is normal to take a tissue biopsy. This involves removing a small part of the lump which is then examined under a microscope to see what sort of cells it contains. Cell samples may also be collected by putting a needle into the lump and sucking out some cells.
Fluid samples may be taken from the airways via a tube placed in the throat, or the digestive system via an endoscope passed into the stomach. In this way your vet can obtain more information without performing a full operation on your dog.
How many tests are needed to diagnose a disease?
With many diseases it is not possible for your vet to come up with an instant diagnosis. Your animal may have to undergo a number of tests so that the vet can rule out possible causes of the illness. While some diseases can be confirmed using a single test, others will need a large number (profile) or a sequence of tests on one or more tissues or body fluids. There are occasions when repeat tests may be needed to be taken over a period of time, eg looking for changes in antibody levels in the blood over several weeks.
Your vet may need to perform diagnostic tests on your dog, or on samples from your dog, to help provide the best possible care for your pet. If you are unsure what a test involves or why your vet needs to do it, please ask for a more detailed explanation.