Creatinine is a breakdown product of muscle metabolism. Its blood level is dependent, among many factors, on age, weight, nutritional status and muscle mass. Hence, creatinine levels in the blood vary from individual to individual. Creatinine is continuously excreted in the urine. Increased blood creatinine is an indication and also a measure of reduced filtration in the kidneys (glomerular filtration rate). Creatinine levels vary between individuals, so an increase in creatinine within the normal range may still be an indication of chronic kidney disease. That is why it is important to measure your cat’s personal creatinine level early on (at least once a year from the age of 5–7). You may, otherwise, only notice a rise in creatinine when it exceeds the normal range, and in chronic kidney disease this could potentially only occur in the later stages. According to the guidelines of the International Renal Interest Society