GFR tells us whether the kidneys are doing their job of filtering waste and excess water from the blood into the urine. Because not all stages of CKD cause symptoms, measuring GFR gives a quick idea of kidney health and helps detect disease in its early stages. GFR is obtained through a blood test that measures creatinine (a waste product of normal muscle breakdown) and calculates how much blood the kidneys can clear per minute. High creatinine levels in the blood indicate that the kidneys are having trouble filtering. Using GFR, the KDIGO guidelines classify CKD into five stages:

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• Stage 1: Normal GFR (greater than 90 mL/min/1.73m²) but with structural abnormalities, protein in the urine, or persistent blood in the urine for longer than 3 months

• Stage 2: GFR between 60 and 90 mL/min/1.73m²

• Stage 3: GFR between 30 and 60 mL/min/1.73m², further subdivided into:

  • Stage 3a GFR of 45 to 60

  • Stage 3b GFR of 30 to 45

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It is important to emphasize that up to Stage 3b, the patient still has CKD but not Chronic Kidney Failure (CKF). In many of these patients, there are no symptoms, which is why CKD is often called a “silent disease” — people usually do not feel anything abnormal until later stages (Stages 4 and 5). CKD generally does not go away but progresses unless early treatment is provided to slow or stop the disease (WorldKidneyDay.org). This is why annual medical checkups are recommended to detect CKD and other diseases early. Progression eventually leads to End-Stage Renal Disease (ESRD), where dialysis or kidney transplant is needed to survive.

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• Stage 4 (CKF): GFR between 15 and 29 mL/min/1.73m² — kidneys have severely reduced function.

• Stage 5 (CKF): GFR less than 15 mL/min/1.73m² — kidneys no longer clear waste effectively; this stage is also known as End-Stage Renal Disease (ESRD) and requires kidney replacement therapy

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 -- When CKD Becomes Chronic Kidney Failure --

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When GFR falls below 30 mL/min/1.73m², the kidneys are no longer able to perform many vital functions, including:​

• Blood pressure control

• Production of erythropoietin (stimulates red blood cell production)

• Regulation of calcium, phosphorus, and electrolytes

• Activation of vitamin D

• Formation of normal urine

• Elimination of toxic waste (ammonia, urea, uric acid, creatinine)

• Metabolism and excretion of medications

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Because of this loss of function, CKF patients often develop high blood pressure, anemia (due to lack of erythropoietin), bone fragility from low calcium and vitamin D, and other complications. In as little as 2 to 3 years, kidney function can decline from 30% down to 15%, causing serious symptoms such as fatigue, swelling, shortness of breath, and more, at which point urgent treatment is needed. This is why, it is extremely important to prevent and avoid the continuing deterioration, even when the kidneys work more than 50%.