Chronic renal insufficiency is characterized by a gradual deterioration of renal function. Depending on the degree of severity, physicians distinguish five stages of renal failure. The glomerular filtration rate serves as the criterion for classification. This laboratory value allows a statement about the extent of renal damage: Normally, various metabolic waste products such as creatinine and urea are excreted via the kidneys. However, the more the kidneys are damaged, the less they are able to filter out such urinary substances. The toxic metabolic waste products then accumulate in the blood, which impairs the function of important organ systems.
Healthy kidneys have a glomerular filtration rate of 95 to 110 ml per minute, which means that the kidneys filter this amount of blood per minute and cleanse it of urinary substances.
Renal insufficiency – stage 1
In the first stage of renal insufficiency the GFR is still more than 90 ml per minute. The creatinine level in the blood is normal, but often there is already an increased amount of protein in the urine – a sign of a disturbance in kidney function. Ultrasound sometimes shows the first pathological changes in the kidneys. Stage 1 renal insufficiency often does not cause any symptoms, but water retention in the tissue (edema) or discolored urine may already be present. In this early stage, however, renal insufficiency is usually only discovered by chance. If the cause of the kidney weakness can be found and treated, it is possible to counteract a further decline in kidney function.
Renal insufficiency – stage 2
Stage 2 renal failure is characterized by a GFR between 60 and 89 milliliters per minute. As before, however, there are usually no abnormalities in the blood. Only a specific examination of the kidney function can reveal the disturbed filter performance.
Renal insufficiency – stage 3
In renal failure stage 3, the GFR is between 30 and 59 milliliters per minute. The filter function of the kidneys is now reduced to such an extent that the blood levels of creatinine and urea increase. At this point at the latest, symptoms occur: High blood pressure, loss of performance and rapid fatigue occur. The probability of cardiovascular diseases increases significantly. If patients are taking drugs that are normally excreted via the kidneys, their dose must be reduced to avoid side effects.
Renal insufficiency – stage 4
If the GFR drops to a value between 15 and 29 milliliters per minute, doctors speak of stage 4 renal insufficiency, which is a significant reduction in renal function and causes increasingly severe symptoms such as loss of appetite, nausea, vomiting, fatigue, itching, nerve and bone pain. In addition, edema is increasingly forming, for example on the legs or around the face.
Renal insufficiency – stage 5
Stage 5 renal insufficiency with a GFR of less than 15 milliliters per minute is also called terminal renal insufficiency, i.e. end-stage renal weakness. The kidney function is now severely restricted or the kidneys fail completely, i.e. they are no longer able to cleanse the blood. This task must now quickly be taken over by a kidney replacement procedure, otherwise, the urinary substances will poison the body: The patient is dependent on blood washing (hemodialysis, HD), abdominal washing (peritoneal dialysis) or kidney transplantation.
Since the waiting lists for a donor kidney are long, patients must be prepared for regular dialysis treatment, often lasting several years. However well this artificial blood filtering works, it cannot completely replace the kidneys: Some of the urinary substances are deposited in the skin, causing a yellowish discoloration and itching. Some patients also develop calf cramps, disturbed perception, cardiac arrhythmia, confusion and even unconsciousness during treatment. Nevertheless, dialysis is absolutely vital in this last stage of renal failure, as long as no donor kidney is available.