Chronic Kidney Disease (CKD) describes a progressive loss of kidney function that develops over months or years. CKD is defined by either kidney damage or a reduced level of function persisting for at least three months. The severity of this condition is classified into distinct stages, which guide monitoring and treatment decisions. Understanding how this illness progresses and how its severity is measured can help people take a more active role in their long-term health.
Understanding Kidney Function and the GFR Measurement
The kidneys perform several functions, primarily acting as the body’s filtration system. They continuously process blood, removing waste products, excess fluid, and toxins, while balancing electrolytes like sodium and potassium. They also produce hormones that help regulate blood pressure and stimulate red blood cell production.
The Glomerular Filtration Rate (GFR) is the metric used to assess filtration performance. This rate represents the volume of blood the kidneys’ tiny filters, the glomeruli, can clean each minute.
Since directly measuring the GFR is impractical for routine care, healthcare providers rely on the estimated GFR (eGFR). The eGFR is calculated using a formula that incorporates the concentration of creatinine in the blood, along with the patient’s age and sex. Creatinine is a byproduct of muscle breakdown, and a rising level suggests the kidneys are not clearing waste efficiently. This estimated number provides a standardized indicator of overall kidney function.
Defining the Stages of Chronic Kidney Disease
The severity of Chronic Kidney Disease is classified into five stages based on the eGFR measurement. This staging framework links the degree of function loss to specific numerical thresholds, providing a standardized way for medical professionals to communicate the extent of the disease.
Stage 1 is characterized by an eGFR of 90 mL/min/1.73 m\(^2\) or higher, meaning function is normal, but there is evidence of kidney damage, such as protein in the urine. Stage 2 indicates a mild reduction in function, with an eGFR ranging from 60 to 89 mL/min/1.73 m\(^2\), still requiring evidence of kidney damage for a CKD diagnosis.
Stage 3 is further divided into two sub-stages. Stage 3A is a moderate eGFR reduction between 45 and 59 mL/min/1.73 m\(^2\). Stage 3B represents a more severe moderate reduction, with the eGFR falling between 30 and 44 mL/min/1.73 m\(^2\).
When the disease reaches Stage 4, the GFR is severely reduced, ranging from 15 to 29 mL/min/1.73 m\(^2\), which is when preparation for kidney replacement therapy typically begins.
Stage 5 represents the highest severity level, known as Kidney Failure or End-Stage Kidney Disease (ESKD). This is diagnosed when the eGFR drops below 15 mL/min/1.73 m\(^2\) or when the patient is already receiving dialysis. At this level, the kidneys have lost almost all their filtering capacity.
Health Consequences Linked to Disease Severity
As kidney function declines through the stages of CKD, the body’s ability to maintain internal balance is compromised, leading to systemic health problems. These complications become increasingly prevalent in Stages 3 through 5.
One common consequence is anemia, which occurs because damaged kidneys produce less erythropoietin, a hormone necessary for red blood cell production. This shortage causes chronic fatigue and generalized weakness.
Fluid and waste retention is another issue, as the kidneys struggle to excrete excess water and toxins. This manifests as edema, or swelling, typically in the ankles, feet, and hands. Fluid buildup also contributes to high blood pressure, which is both a cause and a result of worsening kidney disease.
Mineral and bone disorders develop because the kidneys are unable to regulate the body’s balance of calcium and phosphorus. This imbalance, combined with altered Vitamin D metabolism, can lead to weakened bones, increasing the risk of fractures. CKD significantly increases the risk of cardiovascular disease, which is the leading cause of death for people with the condition.
Management and Treatment Based on Progression
The management strategy for CKD is tailored to the patient’s stage of progression and the severity of associated complications. In the early stages, the focus is primarily on slowing the rate of decline and controlling underlying risk factors. This involves lifestyle changes, such as restricting sodium, moderating protein intake, and maintaining a healthy weight.
Pharmacological interventions are initiated early, primarily controlling blood pressure using medications like Angiotensin-Converting Enzyme (ACE) inhibitors or Angiotensin Receptor Blockers (ARBs). These medications help protect the kidneys and reduce protein leakage into the urine. Patients with diabetes also require strict glycemic control to prevent further damage.
As the disease advances to Stage 4, treatment shifts to preparing for kidney failure. This involves intensive management of complications like anemia and bone disease using specific supplements and medications.
When the disease progresses to Stage 5, the kidneys cannot sustain life, and Renal Replacement Therapy (RRT) becomes necessary. RRT options include dialysis, which filters the blood externally to remove waste and excess fluid, or a kidney transplant, which offers the most effective long-term outcome.