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What is chronic kidney disease?
Chronic kidney disease (CKD) is a condition that develops gradually, where the kidneys' ability to filter blood progressively deteriorates over at least three months. This leads to an accumulation of waste products in the blood, hormonal imbalances, and a disturbance in the body's fluid and electrolyte balance. The disease is divided into five different stages based on the degree of impaired kidney function, which is measured using eGFR (estimated glomerular filtration rate).
Stages and symptoms in chronic kidney disease
The symptoms of CKD are directly linked to the level of impaired kidney function. In the early stages, the disease usually goes entirely unnoticed, whereas advanced stages cause clear signs of urinary changes, fluid retention, metabolic acidosis, anemia, and mineral disorders:
- Stage 1 (eGFR > 90 mL/min) – Normal kidney function with kidney damage: There are signs of kidney damage (e.g., protein in the urine or structural abnormalities), but the filtration capacity is good.
Symptoms: No symptoms. Discovered solely through medical testing.
- Stage 2 (eGFR 60–89 mL/min) – Mildly reduced kidney function: Mild reduction in filtration capacity alongside signs of kidney damage.
Symptoms: Usually completely asymptomatic, as the kidneys are still compensating well.
- Stage 3 (eGFR 30–59 mL/min) – Moderately reduced kidney function: The kidneys' ability to maintain the balance of fluids, salts, and hormones begins to fail.
Symptoms: Can still be subtle, but early signs such as mild fatigue, the need to urinate at night (nocturia), and high blood pressure may develop.
- Stage 4 (eGFR 15–29 mL/min) – Severely reduced kidney function: Advanced kidney disease where waste products begin to accumulate in the blood (uremia).
Symptoms: Clear symptoms such as pronounced fatigue, nausea, loss of appetite, itching, swelling in the legs/feet, and shortness of breath.
- Stage 5 (eGFR < 15 mL/min) – End-stage renal disease (ESRD): The kidneys can no longer maintain life-sustaining functions on their own.
Symptoms: Severe symptoms including severe nausea, vomiting, weight loss, severe itching, fluid accumulation in the body/lungs, and a metallic taste in the mouth. Requires active treatment in the form of dialysis or a kidney transplant.
Common symptoms of chronic kidney disease
Chronic kidney disease can come on insidiously and is difficult to detect without targeted screening as it does not produce any clear symptoms in the early stages. As kidney function deteriorates further, the following symptoms may occur:
- Low energy and fatigue
- Concentration problems
- Nausea and loss of appetite
- Swelling (edema), especially in the legs, ankles and around the eyes
- Foamy urine (proteinuria)
- Increased amount of urine, especially at night
- Itching
- Shortness of breath (may be due to fluid retention or anemia)
What are the causes of chronic kidney disease
Here are common causes of chronic kidney disease:
- Diabetes mellitus (type 1 and type 2)
- Hypertension (high blood pressure)
- Glomerulonephritis (inflammatory kidney disease)
- Polycystic kidney disease (hereditary cyst formation in the kidneys)
- Long-term use of certain medications (such as NSAIDs)
- Age-related decline in kidney function
How can chronic kidney disease be detected?
Chronic kidney disease is often discovered by chance, as the symptoms are often nonspecific and may occur late in the course of the disease. A diagnosis is made using tests:
- Blood test (measurement of creatinine and eGFR – estimated glomerular filtration rate)
- Urine test (analysis of albumin or protein in the urine)
- Blood pressure check
- Ultrasound of the kidneys (to detect structural abnormalities)
It is very important to detect chronic kidney disease early to slow the progression of the disease.
Symptoms vary depending on the degree of kidney function impairment
In CKD, the symptoms are often linked to the degree of kidney function impairment. In mild to moderate kidney disease, symptoms are subtle, while advanced disease can produce clear signs of urinary changes, fluid retention, metabolic acidosis, electrolyte disturbances and hormonal imbalances.
Anemia – common in chronic kidney disease
In CKD, anemia is a common finding and occurs as a result of a deficiency of erythropoietin – a hormone that is normally produced in the kidneys and stimulates the bone marrow to form red blood cells. The anemia is usually normochromic and normocytic, and contributes to symptoms such as fatigue, shortness of breath, headache and pallor.
Phosphate and chronic kidney disease
The regulation of phosphate levels in the body is carried out by the kidneys; in case of impaired kidney function, the excretion of phosphate decreases, which can lead to hyperphosphatemia. High phosphate levels negatively affect calcium balance, stimulate the release of parathyroid hormone (PTH) and can lead to secondary hyperparathyroidism and calcifications in blood vessels and soft tissues. This contributes to an increased risk of osteoporosis and cardiovascular complications.
