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The range of diagnoses to consider, diagnostic tools used and potential treatment or management options for primary, structural problems of a body system are often very different compared to those relevant to secondary, functional problems of that system.

Investigation of primary, structural problems often involves imaging the system in some manner (radiology, ultrasound, advanced trans‐sectional imaging, endoscopy and surgery) and/or biopsy. Routine haematology, biochemistry and urinalysis are often of little diagnostic value. For secondary, functional disorders, on the other hand, haematology and biochemistry are often critically important in progressing our understanding of the case and reaching a diagnosis.

Failure to consider what body system is involved (define the system) and how it is involved (refine the system) can often lead to wasted time and money. This can delay treatment, prolong the disease, prolong the patient’s suffering, sometimes potentially endanger the life of the patient, and may increase unnecessarily the costs to the client, frustrate the vet and client and potentially impair the relationship between vet and client. (Notice a recurring theme here?)

In fact, if you do nothing else when assessing a case before seeking the diagnostic ‘pattern’, ask yourself for each of the specific problems, What system could be involved (i.e. define the system), and how – primarily or secondarily? (i.e. refine the system). This simple question will immediately open your mind to diagnostic possibilities you may never have contemplated if you were just focusing on the ‘pattern’.

Other examples include the following:

 Chronic cough – cardiac or respiratory system? (Chapter 9)

 Jaundice – due to a haemopoietic (haemolysis) or hepatobiliary disorder? (Chapter 11)

 Cardiac arrhythmia – is it due to primary (structural) cardiac disease – for example, dilated cardiomyopathy? Or extra‐cardiac disease – for example, gastric dilation and volvulus, splenic pathology? (Chapter 7)

 PU/PD – is it due to primary polydipsia (the patient wants to drink) or primary polyuria (the patient has to drink)?If due to primary polyuria – is this because of primary (structural) renal disease (e.g. chronic kidney disease) or extra‐renal dysfunction, for example, diabetes mellitus, hypercalcaemia and hypoadrenocorticism? (Chapter 13)

An alternative, although closely related, question for some problems is, Is the problem local or systemic?

 Epistaxis – due to local nasal disease or systemic disease – for example, coagulopathy and hyperviscosity? (Chapter 12)

 Melaena – GI bleeding due to local disease (ulceration – which in turn may be due to primary or secondary GI disease) or systemic disease, for example, coagulopathy? (Chapter 12)

 Seizures – due to local brain disease, for example, neoplasia, infection/inflammation or systemic disease, for example, electrolyte disturbances or intoxication? (Chapter 8)