Tuesday, May 28, 2013

Three things I learned: renal disease in companion animals

Renal disease is a common affliction in elderly feline patients.
There are a lot of online resources available for vets, which is great as one can learn at one's own pace (with one's tiny hound sleeping on the desk beside one's computer if one so desires).

IDEXX have a range of seminars on laboratory testing. I undertook the renal laboratory testing module and picked up a few reminders/pointers. The section on urine cytology was well illustrated and particularly helpful.

Dr Cowell divides primary renal parameters (urea/creatinine/urinalysis) from secondary indicators of renal function (PCV, HGB, reticulocytes, phosphorus, calcium, sodium, potassium, chloride, bicarbonate, anion gap and cholesterol) which I thought was a nice system.

* Inability to concentrate urine is lost when more than 66% of nephron function is lost, while azotemia occurs with 75% loss of nephron function, therefore isosthenuria is an early indicator of chronic renal insufficiency. Persistent isosthenuria and creeping creatinine levels even within normal ranges should ring warning bells.

* Creatinine is a more reliable indicator of glomerular filtration rate than urea.

* Differentials for isosthenuria + azotemia = chronic renal insufficiency, diuretics, corticosteroids, electrolyte derangements (esp hyponatremia, hypokalemia, Addison's disease and hyperadrenocorticism), pyometra (endotoxins inhibit anti-diuretic hormone) and diabetes insipidus.

I liked Dr Cowell's distinction between azotaemia and uraemia. Azotaemia = elevated urea/creatinine and is a laboratory finding. Uraemia = a clinical syndrome (ie azotaemia + nausea/vomiting, oral ulceration/stomatitis, lethargy). Its a simple way to communicate the concept. 

It also served as a good reminder that renal glomerular disease without tubular disease may not lead to azotemia, but usually leads to marked proteinuria (for example in cases of amyloidosis).