In the five stages of kidney disease, each stage is progressively more serious. Kidney disease advances from Stage 1 to Stage 5 as determined by a test called the GFR or glomerular filtration rate. GFR is an indicator of how well the kidneys are filtering the blood. Metabolic consequences of CKD can be devastating:

At Stage 1, when few people are diagnosed, there are few, if any metabolic consequences. Microalbuminuria is often present in some forms of early renal disease especially diabetes mellitus.

By Stage 2, the parathyroid hormone level begins to rise, elevating calcium levels in the blood and increasing the risk of calcification of the arteries and consequently causing premature death. Calcium phosphate product (Ca X P) above 55 is associated with arterial calcification especially in those with hypertension and in smokers.

By Stage 3, calcium absorption decreases. Simultaneously, high density lipoprotein (HDL or “good” cholesterol) activity also declines. This increases the risk of cardiovascular disease if it is not already present. Subsequently, malnutrition and anemia develop.

In Stage 4, triglyceride (blood fat) concentrations rise, metabolic acidosis develops because of excess acidity in the blood. Patients then develop hyperkalemia (high blood potassium). Metabolic acidosis and hyperkalemia can both be fatal. At Stage 4, patients are advised to begin preparing for dialysis or transplantation.

In Stage 5, also called ESRD (end stage renal disease), kidneys have lost more than 85% of their function and the only chance for survival is with dialysis or transplantation. In some healthy elderly persons a reduced GFR that is stable over time and without significant proteinuria may not indicate significant renal disease.