Kidneys perform several functions to maintain health. They filter waste products and excess fluid from the blood, balance minerals like sodium and potassium, and produce hormones that regulate blood pressure and red blood cell production. Kidney function is primarily measured by the Glomerular Filtration Rate (GFR), which indicates how well the kidneys are performing their roles.
Understanding Kidney Function and GFR
The Glomerular Filtration Rate (GFR) indicates kidney health. It estimates the volume of blood that passes through the tiny filtering units in the kidneys, called glomeruli, each minute. A higher GFR indicates better kidney function, as it reflects the efficiency of these filters. GFR is reported in milliliters per minute per 1.73 square meters (mL/min/1.73m²), and can be understood as a percentage of optimal kidney function.
GFR is not measured directly. Instead, it is estimated using a formula that incorporates several factors. This calculation involves a blood test to measure creatinine levels, a waste product from muscle activity. Age, sex, height, and weight are also factored into the equation to provide an estimated GFR (eGFR) that more accurately reflects an individual’s kidney function.
Stages of Kidney Disease
Kidney disease progresses through five stages, categorized by the estimated Glomerular Filtration Rate (eGFR). As kidney function declines, eGFR decreases, and chronic kidney disease (CKD) advances. Recognizing these stages helps healthcare providers manage the condition and anticipate potential complications.
Stage 1 CKD has an eGFR of 90 mL/min/1.73m² or greater, with signs of kidney damage like protein in the urine. In Stage 2, eGFR falls to between 60 and 89 mL/min/1.73m², indicating a mild reduction in kidney function, often without noticeable symptoms. Stage 3 is divided into two substages: Stage 3a (eGFR 45-59 mL/min/1.73m²) and Stage 3b (eGFR 30-44 mL/min/1.73m²). Kidney damage is moderate, and symptoms like fatigue or swelling may appear as waste products accumulate.
Stage 4 CKD means eGFR is between 15 and 29 mL/min/1.73m², signifying severe reduction in kidney function. Patients often experience pronounced symptoms, and discussions about future treatment options, including dialysis, begin. Stage 5 CKD is defined by an eGFR of less than 15 mL/min/1.73m², indicating kidney failure. This advanced stage usually requires kidney replacement therapy, such as dialysis or a kidney transplant, to sustain life.
When Dialysis Becomes Necessary
Dialysis is generally considered when kidney function declines to a very low level, typically a Glomerular Filtration Rate (GFR) of 15 mL/min/1.73m² or less. This corresponds to Stage 5 Chronic Kidney Disease (End-Stage Renal Disease or ESRD), where kidneys function at less than 15% of normal capacity and cannot adequately filter waste and fluid.
The decision to initiate dialysis is not based solely on a specific GFR number. Medical teams also consider the presence and severity of symptoms that arise from the accumulation of waste products in the body. These include severe fluid retention, making breathing difficult, electrolyte imbalances like high potassium, or uremic symptoms such as persistent nausea, vomiting, loss of appetite, fatigue, or confusion.
Uncontrolled high blood pressure, despite medication, or a progressive deterioration in overall health can also prompt the need for dialysis. The choice to begin dialysis is a collaborative one, involving discussions between the patient, their family, and the medical team. This ensures the decision aligns with the patient’s overall health status, quality of life considerations, and personal preferences.
Types of Dialysis
Once the decision is made to begin kidney replacement therapy, two primary types of dialysis are available. Both methods work to remove waste products and excess fluid from the blood when kidneys can no longer function adequately. Understanding these options helps patients and their families prepare for treatment.
Hemodialysis is a process where a machine, called a dialyzer, filters blood outside the body. Blood is drawn from the patient, passed through the artificial kidney to remove waste and extra fluid, and then returned. This treatment typically occurs several times a week, either at a dialysis center or at home.
Peritoneal dialysis utilizes the lining of the abdomen, known as the peritoneum, as a natural filter. A special cleansing fluid, called dialysate, is introduced into the abdominal cavity through a catheter. Waste products and excess fluid pass into this fluid, which is then drained and discarded. Peritoneal dialysis offers more flexibility, as it can often be performed at home, either manually or using a machine overnight.