Chronic kidney disease is divided into five stages by severity.
These stages are determined by measurement of the glomerular filtration rate (GFR), a measure of the filtering capacity of the kidneys, which can be calculated easily from common blood tests. If your physician tells you that you have kidney disease, it’s worth inquiring about the stage, so that over time you can monitor whether your kidney disease is progressing.
Stage 1, the least severe, is defined by a normal GFR, above 90 ml/minute. People with stage 1 kidney disease have either protein loss in the urine or some other evidence of kidney disease, such as scarring on a kidney scan.
Many people with stage 1 kidney disease are able, with treatment, to continue normal kidney function throughout their lives, provided the underlying cause of the kidney disease can be cured or controlled. For example, many diabetic patients in the early stages of their disease may have protein loss in the urine, though initially the GFR may be normal.
Stage 2, or mild chronic kidney disease, is defined by a GFR of 60 to 90. This level of kidney disease also requires careful monitoring and sometimes treatment.
One problem is that the tests available to distinguish the presence of stage 2 kidney disease have some inaccuracy, and it can be hard to distinguish this mild degree of kidney disease from normal kidney function.
Stage 3, or moderate chronic kidney disease, is defined by a GFR of 30 to 60. Most patients with this stage of kidney disease continue to feel well, and many are unaware that they have kidney disease despite the decrease in kidney function.
However, several organ systems start to sustain damage during this stage, including bones, heart and blood vessels, and most patients need medications during this stage to slow the progression of their kidney disease and to protect other organs.
Since there are usually no symptoms evident to patients who have this level of kidney disease, it is important to screen kidney function in people at risk for kidney disease. One of the challenges in stages 1, 2 and 3 kidney disease is to separate out patients who will develop progressive kidney disease from those who are at minimal risk of worsening. One useful way to do this is to measure the amount of protein in the urine, which is quite predictive of future deterioration in kidney function.
During stage 4, or severe chronic kidney disease, with a GFR of 15 to 30, patients need assistance to make a plan for dialysis or transplantation. Unfortunately, it is unusual for patients in this stage to recover, though the rate of progression of their disease can usually be slowed.
Most patients with stage 5 kidney disease (also known as end-stage kidney disease) require dialysis or a kidney transplant to stay alive. Great progress has been made in the care of patients with end-stage kidney disease, but dialysis and transplant are still difficult and time-consuming treatments.