Chronic kidney disease (CKD) is common in both dogs and cats. The incidence of CKD increases with advancing age, and some studies report an incidence of up to 30 per cent in cats over 15 years of age, and up to 10 per cent in geriatric dogs.1,2,3,4
The diagnosis of CKD involves evaluation of the clinical presentation of the patient, blood and urine testing. Testing of urine is essential, and whilst a specific gravity and dipstick are important on their own, a complete urinalysis also involves a microscopic sediment examination to look for cells, casts or any signs of an infection. A urinary protein creatinine ratio should be considered if the urine sediment is inactive to objectively assess the degree of proteinuria. A CBC can help identify if anaemia is present, and check for any signs of inflammation or stress. A serum biochemical profile should at a minimum evaluate urea and creatinine, electrolytes, calcium and phosphate, and protein levels. Typically, there is a loss of concentrating ability when there is approximately 66 per cent loss of nephron function, and azotaemia typically develops when there is approximately 75 per cent loss of nephron function. The sensitivity of creatinine can be increased by trending the creatinine level over time—a significant upward trend in creatinine, even if still within the reference interval, may aid in the earlier diagnosis of CKD.
The recent development of the IDEXX SDMA assay, a new renal function test, is an important advancement in the diagnosis and staging of CKD. SDMA (a methylated form of the amino acid arginine), is produced in every nucleated cell and is released into circulation during protein degradation.
There are three key attributes of SDMA:
1.SDMA is a reliable biomarker of renal function and is almost exclusively excreted by the kidneys. Studies have shown that SDMA is a good biomarker for kidney function in both cats and dogs.6,7
2.It increases earlier than creatinine. Serum levels of SDMA increase when there has been a 40 per cent loss of renal function, and potentially as early as 25 per cent.8,9
3.It is specific for kidney function. SDMA is not affected by lean body mass as creatinine is, and will not be affected
by dietary protein levels, gastrointestinal haemorrhage or hepatic function as
The International Renal Interest Society (IRIS) has provided guidelines on the staging and management of renal disease for a number of years now. The staging has been based on a fasting serum creatinine, and then sub-staging based on arterial blood pressure and proteinuria. IRIS have recently modified their staging guidelines based on the availability of SDMA.12 The SDMA level should always be interpreted in combination with evaluation of serum creatinine and a urinalysis.
SDMA is now exclusively available through IDEXX Laboratories. Please contact IDEXX on 1300 44 33 99 if you have any questions.
References are available upon request.