Diagnostic tests

In order to reach a diagnosis when attending to your horse, your vet may need to take some samples such a blood, urine, skin scrapings, biopsies or faeces. If your horse requires further diagnostic tests more samples may be taken such as fluid from the lungs or the abdomen. But what happens to all these samples and how can they help your vet reach a diagnosis?

There are many different tests which can be carried out on all the various samples that can be collected. Tests carried out on fluids such as urine, peritoneal fluid, fluid from the lungs and biopsies taken from lumps and bumps on your horse include cytology, histopathology and bacterial culture.

Cytology is the study of cells in different tissue fluids.
Each fluid in the body such as blood and urine contains different types of cells which can be examined under the microscope by your vet or a specialist pathologist.

How can cytology help the vet reach a diagnosis?

By looking at the cells present in different fluids your vet can find out a great deal about the organ which produced the fluid or the cavity in which the fluid is found. First of all your vet will make sure that the fluid contains the cells it should contain, then they can see if it contains too many or too few cells, or if there are cells present which shouldn’t be there.
For example if your horse has a respiratory disease a sample of fluid from the lungs can be examined and can tell your vet if your horse has an infection or an allergic disease just by looking at which cells are present. The way the cells look and how old they are reveal a lot about the disease process and help your vet pick the correct treatments.

Histopathology is the study of the microscopic structure of tissues.
Your vet knows how each tissue in the body should look when examined under a microscope and which cells should be present; therefore any changes to the normal architecture and disease processes which change the appearance of the tissue can be picked up when examined under the microscope.

How can histopathology help the vet reach a diagnosis?

The most common use of histopathology is for looking at biopsies taken from lumps and bumps. Your vet will have an idea about what may be causing a particular lump but histopathology can help with a precise diagnosis and tell us about the way the lump is interacting with the surrounding tissue.
When the biopsy is taken it is sent to a laboratory where it is cut into smaller pieces and stained with special dyes which allow the pathologist to see the different cells.
Histopathology is particularly helpful in determining if a lump is a benign mass or a malignant tumour and so it helps your vet chose the correct treatment.

If your vet suspects that your horse has an infection they may wish to send the samples they take for bacterial culture, i.e. try and grow bacteria from the sample and see which bacteria are present. In order to grow bacteria from a sample it is placed on a special gel which contains all the nutrients the bacteria might need to grow – some bacteria may take up to a week to grow.
If bacteria does grow from the sample your vet can also test to see which antibiotics will work against that bacteria so that the most appropriate antibiotic can be selected – this is called a sensitivity test.