Further diagnostic tests

After performing a complete clinical examination, including visual inspection, palpation and auscultation, the vet may need to perform additional examinations to reach a more precise diagnosis. Many diseases share the same symptoms and it can be impossible to determine the exact cause of an illness on the basis of the symptoms alone.

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Haematology

Haematology is the microscopic examination of the cells present in the blood stream, both quantitative (number of cells present) and qualitative (type and appearance of the cells). Clearly, haematology necessitates the withdrawal of a blood sample.

The numbers of each cell type are counted, and their appearance observed on a blood smear (a drop of blood is spread onto a microscope slide).

Red blood cells (erythrocytes) transport oxygen to the tissues. Their numbers may be reduced, for example following haemorrhage, leading to anaemia. White blood cells (leucocytes) are classified into several different categories depending on their function. An increase in leucocytes is indicative of inflammation in the body, which may be caused by an infection, parasite burden or some types of tumours, etc. Their numbers may also decrease in diseases which lower the immune response. Platelets (thrombocytes) play an essential role in coagulation (clotting), and therefore the cessation of bleeding in the event of a wound.

© Diffomédia/Royal Canin
© Diffomédia/Royal Canin

Numerous diseases may cause haematological modifications. Monitoring these parameters provides an indication of the effects of the disease on the body and the type of causative agent (infectious, autoimmune, etc.). On its own, this examination rarely provides a definitive diagnosis.

Clinical biochemistry

Clinical biochemistry is the determination of the concentration of the molecules found in the body fluids (blood, urine, cerebrospinal fluid, etc.). It is used to identify any changes in organ function and sometimes structural changes. In elderly dogs, biochemical monitoring can be used to detect changes in organ function before the onset of the first clinical signs. Preventative medical treatment can then be implemented.

The choice of molecules to be examined is made as a function of the dog's symptoms, or of the organ that is thought to be dysfunctioning. Below are a few examples of some of the parameters that can be measured:

- urea, creatinine (renal dysfunction)

- glucose (diabetes for example)

- ALP, ALT, AST (hepatic dysfunction)

- electrolytes (calcium, potassium, sodium, etc.), all changes which can have serious consequences for the dog’s health.

- Hormones (thyroxine for the thyroid gland, cortisol for the adrenal glands, etc.)

When an anomaly is detected, the progression of the disease can be monitored with regular blood tests.

Urinalysis involves

Urinalysis involves the detection of the presence of certain elements in the urine. The sample is either collected into a container when the dog urinates or withdrawn
directly from the bladder using a needle (cystocentesis) by the vet, or by inserting a urinary catheter. There are various possible examinations:

- Urine dipsticks provide a quick and easy means of detecting pathology of the urinary tract. These “sticks” comprise several coloured indicators that change colour as a function of the presence, absence, or concentration of various elements. They can be used to detect the presence of blood, proteins, leucocytes, glucose, ketones and to determine the pH level of the urine. Owners of diabetic dogs often perform the test at home to adjust the treatment themselves.

- Bacteriological analysis, which is performed if bacterial cystitis is suspected following the dipstick test.

- Microscopic analysis of the elements present in the urine in which the exact nature of any urinary stones is determined. It is essential to implement effective prevention by adapting the diet to prevent the onset or build-up of these calculi (stones) in the bladder.

© WCPN

Coprology

Faecal analysis is the examination of the dog’s stools, and is useful for detecting parasites. The faeces are first analysed without the microscope (some worms can be seen with the naked eye), then under the microscope. A single faecal culture is not enough to determine whether worms are present or not, and the vet usually needs to take several samples. Microscopic examination of the faeces provides information as to the exact nature of any parasites, which is vital for choosing the most appropriate wormer.

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Why should I collect my pet faeces for analysis?

When your vet asks you to collect your pet's faeces you feel it´s a nasty task and besides if there are so many medicines to worm pets why don´t give it a pill and that´s all?

Many different parasites including worms live in the gut and produce eggs in the faeces that can be studied and identified with faecal analysis. Some of these produce diarrhoea or vomiting and some no apparent illness until the pet is injured, the immune system suffers and the worms start sucking blood or causing other damage. Unfortunately, different worms have different life cycles so antiparasitic drugs must be given at different intervals. Moreover not every worm is killed by the same drug which is why we must know who the enemy is in order to give the best treatment in the most appropriate period.

© Pérez Tort

Gabriela Pérez Tort, DVM
Veterinary Faculty of Parasitology and Parasitic Diseases
University of Buenos Aires (Argentina)

Medical imaging

Medical imaging comprises various techniques whose objective is to visualise the internal structures of the body (organs, bones, vessels, etc.) and sometimes to see whether they are functioning correctly. It provides the opportunity to explore the body without the need for invasive surgery. The imaging technique is chosen depending on the type of structure to be studied.

© Grossemy/Cerca CHV/Frégis

Radiography and CT-scans use X-rays. These penetrate the body to varying extents depending on the density of the structures that they encounter. Radiography is extensively used to examine bone lesions and is widely available. The CT-scan provides improved definition and enables fine sections to be made of the structures. However, the latter is not widely available in veterinary medicine.

Ultrasonography works by sending ultrasound waves through a structure. These waves are then returned to the probe at varying directions and intensities depending on the structures they encounter. This method makes it possible to visualise cross-sections of the organs and is currently widely used to investigate abdominal and cardiac diseases. The use of Doppler enables the visualisation of blood flow in the vessels.

MRI (Magnetic Resonance Imaging) uses a magnetic field to generate images. This examination requires general anaesthesia. The images obtained provide excellent contrast, even within an organ, which can be used to detect brain tumours for example. It is primarily used for the diagnosis and monitoring of neurological problems. It is not yet widely available in veterinary medicine.

Scintigraphy uses a radiographic tracer (for example radioactive iodine). The movement of this tracer in the body is followed and the data is analysed by a computer, which reveals the zones that accumulate and use the tracer. This technique provides interesting information on a functional level but is not widely used. Animals which undergo the examination and their excreta remain radioactive for several days after the end of the examination, which can pose health and safety problems for humans.

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Echocardiography

© ENVA-Cardio/Duhayer/Royal Canin

Echocardiography has been a very important tool in human and veterinary cardiology for more than 30 years. Technological developments over the past decade have widened the scope of application considerably. Three methods are currently used, M-mode, two-dimensional (2D) and Doppler. The last of these has become most widespread, including spectral Doppler, colour Doppler and tissue Doppler. The aims of a conventional echocardiograph examination are as follows:

- Evaluating heart anatomy and adjacent structures by the 2D mode.

- Measuring the various heart chambers precisely.

- Evaluating the blood flow through the valves by pulsed and continuous Doppler.

The incorporation of all these modes permits an evaluation of the heart anatomy, the integrity of the heart valves, the systolic and diastolic function, and indirectly the estimation of endocardiac pressure and the pressure between the pulmonary artery and the aorta. Doppler tissue imaging (DTI) is a more recent so-called conventional ultrasound technique which allows the quantification of the regional, radial and longitudinal myocardial region by measuring the speed of movement of the myocardium in real time. DTI is a non-invasive method for analysing regional myocardium movements, using DTI 2D colour, which, unlike the two other modes (pulsed DTI and colour M-mode DTI), allow the simultaneous quantification of the speed of several myocardial segments belonging to one, two or three different walls, thus providing a precise evaluation of intra- and interventricular myocardial synchronism. Potential applications of DTI in cardiology are extremely promising. The advantage of this imaging technique is that, like conventional ultrasonography, it does not involve bleeding. It also appears to be more sensitive to detecting myocardium alterations at an early stage in humans and dogs, which means it could potentially be used for the early detection of some heart diseases in veterinary medicine (dilated cardiomyopathy in dogs and hypertrophic cardiomyopathy in cats, for example).

© Gouni
© Chetboul

Vassiliki Gouni, Veterinary surgeon
Professor Valérie Chetboul, Veterinary surgeon
Cardiology Unit National Veterinary College Alfort,
(France)

Histology

Histology is the microscopic observation and analysis of tissue samples. When an anomaly is found in an organ, simple visual observation is often insufficient to determine the exact nature of the problem. The sample can be taken during surgery (for example, following the removal of a tumour), by biopsy (sampling of a small fragment of tissue) or sometimes at post-mortem. The tissue is fixed and sections are made. A coloured stain is often needed to differentiate the different cell types. The observer looks for structural anomalies in the tissue and the types of cells present, and correlates their observations with those made during the clinical examination of the dog. This analysis is very important for suspected cases of cancer, as it provides an exact determination of the nature of the tumour and therefore provides a prognosis.

Endoscopy

Under general anaesthesia, a camera is introduced using a flexible tube into one of the body’s tracts or cavities that cannot be explored with the naked eye. This method is essentially used to diagnose diseases affecting the respiratory and gastrointestinal tracts. Access to these cavities is achieved by the natural routes. Samples (biopsies) for histological analysis are sometimes taken at the same time.

Electrocardiogram (ECG), electroencephalogram (EEG) and electromyelogram (EMG)

These three techniques all analyse the electrical properties of a structure to provide information about its function.

To perform an ECG, electrodes are placed on the skin surface to record the electrical activity of the heart. The resulting graph is analysed to provide information about heart function and provide an early diagnosis of dysfunction or disease.

An EEG is performed by placing electrodes on the clipped skin of the dog’s head to provide a record of the electrical activity of the brain. The regularity, quantity and location of the waves are analysed. Not widely available, this examination is currently more widely used in research than for diagnostic purposes.

An EMG involves stimulating muscle contractions by sending an electrical impulse through the nerve that controls the contraction of a specific muscle. The speed of transmission of the electrical impulse is measured by the delay between the electrical stimulation and the contraction of the muscle. When a nerve is damaged, transmission is altered (slowed or absent if the nerve has been completely sectioned).

Hearing tests

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Hearing tests are strongly advisable in certain breeds of dog, notably Dalmatians.

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AEP (Auditory Evoked Potential) tests involve recording the electrical activity of the cochlea (internal structure of the ear) following acoustic stimulation. This examination is performed under sedation by a specialist veterinarian. Each ear is assessed separately. This examination is strongly advisable in certain breeds of dog, notably Dalmatians, in which 15 % of puppies are born with unilateral deafness and 5% with bilateral deafness.

© Diffomédia/Royal Canin

Ophthalmological tests

© Duhayer/Cogis

Following an external examination of the eye, the veterinarian may need to examine the internal structures of the eye: lens, retina, optic disc. The optic disc is an area of the retina on which the size and shape of the blood vessels, colour and general homogeneity give information about the condition of this structure, which receives visual information. This examination is performed using an ophthalmoscope. In the event of an anomaly, it is repeated on a regular basis to monitor the progression of the disease.

An electroretinogram assesses the electrical response of the retina to stimulation with flashes of white light (diurnal vision) and blue light (night vision). It enables the detection of functional anomalies of the retina. Prior to the arrival of genetic testing, this examination was used to screen for progressive retinal atrophy, which affects numerous breeds particularly the Cocker Spaniel and Labrador.

Dermatological tests

© Duhayer/Royal Canin

The vet may take samples of cutaneous lesions to determine the cause of disease. The collection of a few hairs, which are then examined under the microscope, can be useful for detecting the presence of parasites. A skin scrape using a scalpel blade is used to take a sample of the superficial cells of the skin and any bacteria or parasites that can then be examined under the microscope after staining. This makes it possible to adapt the treatment to the cause.

An ear swab involves taking a sample of the cells and wax from the ear using a swab. The swab is then spread onto a slide, stained and analysed. This enables the detection of individual bacteria, fungi, etc. which cause otitis and can then be treated with a specific treatment.

© Diffomédia/Royal Canin
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