Understanding Laboratory Tests in Chronic Kidney Disease

Presenter – Nick Carmichael BVM&S, BSc VetSci(Hons), Diploma VCS(Syd), Diploma RC Path,
Diplomate

When starting my career fifteen years ago, most cats suffering from Chronic Renal Failure (CRF) presented at the very latter stages of the disease. These often emaciated cats were difficult to manage and any improvement seen was often short lived. Fortunately, with improved diagnostics and treatment options, this no longer has to be the case, allowing us to manage both feline and canine cases with greater success.

‘The Webinar Vet organised Nick Carmichael to speak at last week’s veterinary webinar covering advances in diagnosis of CRF in conjunction with a set of guidelines set up by the International Renal Interest Society (IRIS).

So what’s changed from my early days in practice? Mr Carmichael explained the pathogenesis of CRF is now much better understood, with diagnosis of CRF and management of systemic effects such as hypertension being achieved at a much earlier stage. A set of IRIS guidelines has also been developed by a panel of experts within the field of renal medicine. These guidelines cover a series of tests which can be used to stage CRF and offer a standardised treatment plan dependent on the staging of the disease.

Creatinine is one of the laboratory tests necessary to fulfil the staging process offered by the IRIS guidelines. Mr Carmichael explained that increased creatinine levels can be due to pre-renal, renal and post-renal causes. Urinalysis must be performed to differentiate between pre-renal and renal with a concentrated urine (SG>1.030 in dogs,>1.035 in cats) indicating that increased creatinine is secondary to pre-renal causes. Post renal causes can only be ascertained from the clinical presentation of the patient.

Unfortunately, increases in creatinine secondary to renal changes is only seen when 75% of renal function has been lost, and an inability to concentrate urine is seen when 50% of function has been lost. Interestingly if the urine is hyposthenuric, it indicates that renal function is good as considerable effort is needed by the kidneys to actively dilute urine.

The IRIS guidelines stage CRF partly according to the level of creatinine measured, and these values can cross over into ‘normal’ laboratory reference ranges. Urinalysis is therefore essential in working up these cases, even if creatinine levels fall within normal limits.

Phosphate levels also play a key role in assessing renal function and managing progression of CRF according to IRIS guidelines. Excess phosphate can also lead on to secondary renal hyperparathyroidism with both phosphate and PTH having deleterious effects directly on the kidneys. Managing PTH and phosphate levels by using diet and phosphate binders significantly reduces mortality rates, and IRIS guidelines have target phosphate levels making continual monitoring essential. Calcitriol (Vit D supplementation) is becoming increasingly used in the USA, and in a randomised controlled clinical trial of 37 dogs, the mortality of dogs given Calcitriol was less than 50% of the control group.

Proteinuria and blood pressure are also key diagnostic tests forming part of the IRIS guidelines and were discussed further within this veterinary webinar. Mr Carmichael explained in much greater depth the value of many laboratory tests for diagnosing CRF and the massive benefits that we and our patients can reap by following these guidelines. I am glad to say that I am now rarely confronted by the emaciated, dehydrated cat at the end stages of kidney failure. The patients I see are caught early by regular screening, by taking even minor weight loss seriously, and testing patients early. By following the IRIS guidelines, management of these cases is becoming increasingly successful offering a much better quality of life for patients; long may it continue.

The Stethoscope MRCVS

To purchase access to this webinar please click the button below

buy now 2