Diagnosing Feline Chronic Kidney Disease (CKD)
Diagnosing CKD
CKD is defined as "presence of structural or functional abnormalities of one or both kidneys that have been present for an extended period, usually 3 months or longer."
To diagnose CKD, your veterinarian will examine your cat, probably at least twice, and may take blood and urine tests, and imaging tests (x-rays or ultrasonography). In blood tests, your veterinarian will especially consider the concentration of creatinine and symmetric dimethyl arginine (SDMA) in the blood, both commonly used indicators of kidney function. In urine tests, the urine specific gravity is often used, among many other indicators. Together, these tests provide a comprehensive understanding of the kidney function.
IRIS staging
CKD is generally classified into four stages using blood creatinine and SDMA concentration according to the guideline provided by the International Renal Interest Society (IRIS) (Table 1).
According to the IRIS staging guidelines, a cat with CKD can be categorized into four stages: stage I to IV. As the stages go up, the CKD progresses and the kidney function declines. CKD can be categorized further into substages according to urine protein levels (urine protein creatinine ratio; UPC) and blood pressure. This staging and substaging system allows veterinarians and owners to gain an understanding of the necessary treatment and management of CKD, which differs greatly according to each point in progression of the disease.
Table 1. CKD Stages and Their Characteristics (IRIS CKD Guidelines -modified 2023)
| Stage | sCr level (mg/dl) |
SDMA level (μg/dl) |
Stage description |
|---|---|---|---|
| Stage I (Non-azotemic CKD) |
<1.6 | <18 | Normal blood creatinine concentration. Normal or mild increase in blood SDMA concentration. Other abnormalities in the kidney may be present (such as inadequate urine concentrating ability and proteinuria). |
| Stage II (Mild azotemia in kidney) |
1.6～2.8 | 18～25 | Normal or mildly increased creatinine or SDMA. Clinical symptoms are absent or, if present, generally mild. |
| Stage III (Moderate azotemia in kidney) |
2.9～5.0 | 26～38 | Many clinical symptoms are present in varying degrees. In early stage III, no clinical symptom is usually found. In late stage III, there will be several clinical symptoms, some of which may be severe. |
| Stage IV (Severe azotemia in kidney) |
>5.0 | >38 | Many severe clinical symptoms are present. |
Azotemia: increased blood creatinine levels
If the cat is underweight, SDMA concentration is a more accurate indicator of kidney function than sCr concentration.