Kidney Function: Tasks, Measurement & Health

What Is Kidney Function?

Kidney function refers to the essential tasks performed by the kidneys to maintain the body´s internal balance. The two kidneys are bean-shaped organs located in the back of the abdominal cavity. Each day, approximately 180 liters of blood pass through the kidneys, where waste products, excess salts, and metabolic byproducts are filtered out and excreted in the urine. Healthy kidney function is critical for overall wellbeing and the proper functioning of virtually every organ system.

Functions of the Kidneys

The kidneys perform several vital roles in the body:

• Blood filtration: In tiny structures called glomeruli, the kidneys filter the blood, removing waste products such as urea and creatinine.
• Fluid balance regulation: The kidneys control how much water is retained in the body and how much is excreted through urine.
• Electrolyte regulation: Sodium, potassium, calcium, and phosphate levels are carefully controlled by the kidneys to support muscle, nerve, and heart function.
• Acid-base balance: The kidneys help maintain the blood pH within a narrow range by excreting or retaining acids and bases.
• Hormone production: The kidneys produce important hormones, including erythropoietin (stimulates red blood cell production), renin (helps regulate blood pressure), and activated vitamin D (promotes calcium absorption in the intestine).

Measuring Kidney Function

Kidney function is primarily assessed using the glomerular filtration rate (GFR), which indicates how much blood is filtered by the kidneys per minute. A healthy adult typically has a GFR of around 90–120 ml/min. Other important laboratory markers include:

• Serum creatinine: Elevated creatinine levels suggest reduced kidney function.
• Blood urea nitrogen (BUN): High urea levels may indicate kidney impairment.
• Proteinuria: The presence of protein in the urine is an early sign of kidney damage.

Impaired Kidney Function

Impaired kidney function -- also referred to as renal insufficiency or kidney failure -- can occur acutely or develop chronically over time. In chronic kidney disease (CKD), the filtering capacity of the kidneys gradually declines over months or years. Common causes include:

• Diabetes mellitus (diabetic nephropathy)
• High blood pressure (arterial hypertension)
• Inflammatory kidney diseases (glomerulonephritis)
• Long-term use of certain medications (e.g., non-steroidal anti-inflammatory drugs)
• Genetic conditions such as polycystic kidney disease

Symptoms of Reduced Kidney Function

In its early stages, reduced kidney function often causes no noticeable symptoms. As the condition progresses, the following symptoms may appear:

• Fatigue and general exhaustion
• Fluid retention (edema) in the legs, feet, or face
• Changes in urine volume or color
• High blood pressure
• Nausea and loss of appetite
• Itching
• Shortness of breath in advanced stages

Maintaining and Supporting Kidney Health

To preserve kidney function over the long term, healthcare professionals recommend the following measures:

• Stay well hydrated -- generally 1.5 to 2 liters of water per day
• Keep blood pressure and blood sugar levels well controlled
• Adjust salt and protein intake if kidney disease is present
• Have kidney function values checked regularly by a doctor
• Avoid nephrotoxic substances (agents that are harmful to the kidneys)
• Quit smoking and limit alcohol consumption

References

1. Kidney Disease: Improving Global Outcomes (KDIGO) -- Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease. Kidney International Supplements, 2013.
2. Brenner, B. M. (ed.) -- Brenner and Rector's The Kidney. 10th edition. Elsevier Saunders, 2016.
3. World Health Organization (WHO) -- Chronic kidney disease. Fact Sheet, 2023. Available at: https://www.who.int