How Much Do You Know About Diabetes and Kidney Disease?

By Alasdair Wilkins

Our overview of what all of us need to know about one of our most vital organs – our kidneys.

This article was rewritten in 2020; read it here.

What do the kidneys do?

The kidneys serve multiple crucial functions in the human body. Their primary purpose is to filter waste products out of the blood and other bodily fluids. This process creates urine and allows the body to reabsorb glucose. The kidneys also help maintain the optimal blood pressure and produce several vital hormones.

What is chronic kidney disease?

Also known as chronic renal disease or nephropathy, chronic kidney disease (CKD) occurs when the kidneys are unable to properly filter all the fluids that pass through them. CKD can present a wide variety of symptoms, with most being traced to the buildup of waste products in the blood that should have been released through urine.

Protein can also be lost in the urine when kidneys aren’t working properly – when kidney disease is just beginning, this is called “microalbuminuria” (small amounts of protein in the urine), but over time can worsen to “macroalbuminuria” (over 300 mg of protein in the urine each day).

How is diabetes related to chronic kidney disease (CKD)?

According to the American Kidney Fund, diabetes is the primary cause of chronic kidney disease, accounting for 38% of all CKD cases in the United States in 2012. The other major cause of CKD is hypertension (25%), which itself is an extremely common complication of diabetes. About 40% of people with diabetes (roughly 11.6 million people) are expected to develop CKD. CKD is a common complication for both type 1 and type 2 diabetes.

How can CKD be treated?

The majority of CKD cases involve damage to the kidney’s blood vessels, although there are several possible underlying causes for the progressive loss of renal function. Indeed, this makes treating CKD complicated – while certain forms of CKD can be treated depending on the specific cause, there are no universally successful treatments known to slow down or reverse the loss of kidney function. CKD can ultimately result in kidney failure, which can only be treated with dialysis or a kidney transplant.

How can kidney function be improved?

Several lifestyle factors can potentially improve kidney health. According to the CDC, these include maintaining good glucose control, keeping blood pressure below 140/80 mm Hg, keeping cholesterol in the target range, exercising and generally being physical active, eating healthily, and cutting down salt intake. These can all potentially slow down the loss of kidney function, especially when combined with the right medications.

What is GFR?

GFR stands for glomerular filtration rate. This simply refers to the rate at which filtered fluids move through the kidney. Since CKD involves a slowdown of the movement of filtered fluids through the kidney, GFR is the main measuring stick used to determine how well the kidneys are working. GFR is measured in ml/min/1.73m² – those units simply refer to how many milliliters (ml) are filtered every minute (min), adjusted for the standard value for the body’s surface area (1.73m²).

What is eGFR?

The early phases of chronic kidney disease often do not present any noticeable symptoms – this makes blood tests that can calculate GFR and thus kidney function extremely important, as they are one of the only ways to detect CKD. Such a blood test produces an estimated GFR, or eGFR for short. This value is used as the basis for assessing a person’s kidney function.

How is renal health defined?

In adults, the healthy GFR range is 100-130 ml/min/1.73m². CKD is divided into five stages based both on eGFR score and kidney damage.

Stage 1 of CKD is slight renal impairment, defined as visible kidney damage with GFR at or above 90.
Stage 2 is mild impairment, or GFR of 60-89.
Stage 3 is mild to moderate impairment, or GFR 30-59.
Stage 4 is severe impairment, or GFR of 15-29.
Kidney failure occurs when GFR is below 15, which is also known as Stage 5 or end stage renal disease.

Anyone with a GFR below 60 ml/min/1.73m² for at least three months is considered to have chronic kidney disease, regardless of whether there is visible evidence of kidney damage.

[Editor's note, this article was originally published as an appendix in "What Invokana's Day at the FDA Means for the Future of Type 2 Diabetes." It has been updated since its original publishing.]

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