Toxic, nitrogen-containing urinary substances responsible for uraemiaA raised level in the blood of urea and other urinary substances, which in chronic kidney disease can no longer be adequately excreted due to impaired renal function (glomerular filtration rate). This leads to renal damage due to uraemic toxins, toxic urinary substances The symptoms... and kidney damage. The concentration of these substances can increase in the blood if the filtration ability of the kidneys (glomerular filtration rateThe glomerular filtration rate (GFR) is defined as the volume of fluid that is filtered by the glomeruli of the nephrons of both kidneys per unit of time to produce primary urine. It is, therefore, the chief measure of kidney function. The rate corresponds to...) is reduced. The uraemic toxins can then directly damage the kidneys and lead to the symptoms associated with uraemia. The best-studied uraemic toxins include indoxyl sulphate, which contributes directly to the progression of renal failureLoss of kidney function, which may be sudden (acute) or gradual (chronic), as in chronic kidney disease. Loss of kidney function leads to a reduced filtration capacity (glomerular filtration rate) and, thus, an inability to sufficiently filter out urinary substances such as uraemic toxins. Renal... in CKD and can impede blood formation, and para-cresyl sulphate.