What are the kidneys used for?

The kidneys are essential to life. The kidney has several functions, including what is known as a filtering role:

• It eliminates waste products (urea and creatinine) carried by the blood and excretes them in the urine.
• It keeps the body's water and mineral salts (sodium and potassium) constant by adjusting their elimination through the urine.
• It also produces hormones and vitamins that are essential for certain functions:

- The production of red blood cells by the bone marrow thanks to erythropoietin (EPO),
- Regulating blood pressure by balancing the production of hormones (renin and angiotensin),
- Maintaining bone quality by producing the active form of vitamin D.

Renal failure is the consequence of the progression of diseases that destroy the kidneys.

The body is gradually poisoned by waste products that are no longer eliminated by the kidneys.
Kidney failure is said to be chronic when this loss of function is progressive and the damage to the kidneys is permanent. In many cases, it progresses gradually over several years.
Kidney function is measured by the level of creatinine in the blood, but this level varies with the person's muscle mass and sex. This is why the degree of renal failure is defined by glomerular filtration rate, measured by creatinine clearance, which is more accurate.

According to the French classification, there are 4 stages of renal failure:

• Stage 1: Chronic kidney disease without renal failure: clearance greater than or equal to 60 ml/mn/1.73 m2
• Stage 2: Moderate renal failure: clearance between 30 and 59 ml/mn/1.73 m2
• Stage 3: Severe renal failure: clearance between 15 and 29 ml/mn/1.73 m2
• Stage 4: End-stage renal failure: clearance of less than 15m1/mn/1.73 m2
• End-stage renal disease is the final stage of chronic renal failure: the loss of renal function is such that the patient's life is in danger in the short term. The kidney is no longer able to eliminate toxins and potassium.
  Hyperkalaemia (too much potassium in the blood) can lead to cardiac arrest.
  Daily urinary elimination (diuresis) is poorly adapted, leading to water and salt overload. This water and salt overload can also lead to high blood pressure.
  In addition, the deficient production of erythropoietin by the diseased kidney leads to anaemia.