The kidneys are two bean-shaped organs, each about the size of a fist, located just below the rib cage on either side of the spine. Their primary function involves filtering waste products and excess water from the blood to produce urine. Beyond waste removal, kidneys also play a significant role in maintaining the body’s fluid balance, regulating blood pressure, and producing hormones that support red blood cell production and bone health. When kidneys become damaged over time, they may lose their ability to perform these functions effectively, leading to a condition known as chronic kidney disease (CKD). CKD is a progressive illness where kidney function gradually declines.
Understanding Kidney Function Measurement
Kidney function is primarily assessed using a measure called the Glomerular Filtration Rate (GFR). GFR quantifies the volume of blood filtered by the glomeruli—tiny filtering units within the kidneys—each minute. A higher GFR indicates better kidney function, as it signifies that the kidneys are efficiently removing waste from the bloodstream. In clinical practice, GFR is typically estimated (eGFR) rather than directly measured due to the complexity of direct measurement methods. This estimation commonly relies on a simple blood test that measures creatinine levels. Creatinine is a waste product from muscle metabolism that healthy kidneys filter out of the blood. The eGFR calculation also considers factors such as a person’s age, sex, and sometimes height or weight to provide a more accurate estimate.
Stages of Kidney Disease Progression
Chronic kidney disease is classified into five stages based on the estimated Glomerular Filtration Rate (eGFR), which indicates the level of kidney damage and function. These stages help healthcare providers determine the severity of the disease and guide treatment plans.
- Stage 1 CKD is characterized by an eGFR of 90 mL/min/1.73 m² or greater, indicating normal kidney function despite some evidence of kidney damage, such as protein in the urine.
- Stage 2 involves a mild decline in kidney function, with an eGFR ranging from 60 to 89 mL/min/1.73 m².
- In Stage 3, kidney function shows a moderate decline, with eGFR values between 30 and 59 mL/min/1.73 m², often split into 3a (45-59) and 3b (30-44).
- Stage 4 CKD signifies a severe reduction in kidney function, with an eGFR between 15 and 29 mL/min/1.73 m².
- The final stage, Stage 5 CKD, is defined by an eGFR of less than 15 mL/min/1.73 m², indicating kidney failure, also known as End-Stage Renal Disease (ESRD).
The Dialysis Threshold
Dialysis is a medical treatment that takes over the functions of failing kidneys, removing waste products and excess fluids from the blood. It is typically considered when kidney function declines to Stage 5 Chronic Kidney Disease (CKD), specifically when the estimated Glomerular Filtration Rate (eGFR) falls below 15 mL/min/1.73 m². While an eGFR below 15 mL/min/1.73 m² is a general guideline, it is not an absolute cutoff. The decision to initiate dialysis is highly individualized and involves a comprehensive assessment of a patient’s overall health and specific circumstances. Some individuals may begin dialysis with an eGFR slightly above this threshold if their symptoms warrant immediate intervention. Conversely, others with an eGFR below 15 may not start dialysis right away if they are managing well without severe symptoms.
Considerations Beyond GFR
While a low GFR is a key indicator for dialysis, other important factors influence the decision to begin treatment. The presence of severe symptoms often prompts the initiation of dialysis, even if the GFR is just above the typical threshold. These symptoms can include persistent nausea, vomiting, or severe fatigue. Complications that are difficult to manage with medication also play a role. These might include uncontrollable fluid overload, leading to severe swelling and shortness of breath, or dangerously high potassium levels (hyperkalemia) that can affect heart function. Uremic pericarditis, an inflammation of the sac around the heart caused by kidney failure, often necessitates dialysis. The patient’s overall health, quality of life, and personal preferences are also considered in this shared decision-making process between the patient and their healthcare team.