Diabetic kidney disease (DKD) is a common and serious complication of diabetes. Kidney failure can cause death or contribute to death from heart disease or stroke. Along with high blood pressure, diabetes is the leading cause of kidney disease, with 20% to 40% of people with diabetes having some level of DKD. But like all complications, DKD can be prevented, slowed or reversed with good treatment and self-management.
The kidneys are among the greatest miracles of the human body. These bean-shaped organs, each about 4 inches (11 centimeters) long in adults, constantly take waste products and extra water out of the blood and excrete them in the urine. Without working kidneys, toxins and water would build up in the blood and rapidly kill us. According to the National Kidney Foundation, “Your kidneys filter about 200 quarts of blood each day to make about one to two quarts of urine.” An average adult human has about five quarts of blood, so most blood goes through the kidneys about 40 times each day.
Kidneys do their magic with about a million mini-organs called nephrons (NEFF-ronz). That’s why kidney doctors are called nephrologists. Each nephron contains a tuft of tiny blood vessels called a glomerulus (glow-MARE-you-liss), an amazing filtering system that pushes out poisons like ammonia and keeps important body proteins in. Then a second set of filters called the renal tubules reclaim escaped proteins and glucose.
Like all blood vessels, nephrons are easily damaged by high levels of glucose (sugar) in the blood. Sugar inflames blood vessels and causes swelling and scarring. When a glomerulus is damaged, it will excrete proteins that the body needs to keep. In later stages, some nephrons shut down completely and excess water cannot be excreted.
Like diabetes, kidney disease is a silent killer. “Those with kidney disease tend not to experience symptoms until the very late stages,” says Joseph Vassalotti, MD, chief medical officer at the National Kidney Foundation. “Only 10% of people with chronic kidney disease know that they have it.” There are a few symptoms. Dr. Vassalotti cites fatigue; difficulty sleeping; dry, itchy skin; blood in the urine; bubbly urine; swelling around the eyes, ankles or feet; poor appetite; and muscle cramps as possible warning signs. The Mayo Clinic adds nausea, vomiting and decreased mental sharpness to this list. But since all those symptoms can result from a variety of conditions, it’s hard to tell much about the kidneys from symptoms alone in the early stages.
Because it can be difficult to distinguish DKD from other conditions in the early stages, experts advise people with diabetes to have their kidneys tested regularly. A blood test for creatinine, a waste product our bodies constantly produce and excrete, can be used to calculate an estimated glomerular filtration rate (eGFR), which indicates how fast the kidneys are processing urine. A normal range is 90 milliliters per minute or above.
Kidney function is also monitored with tests for blood urea nitrogen (BUN). Normal BUN ranges are 8 mg/ dl to 24 mg/dl for men and 6 mg/dl to 21 mg/dl for women. For an eGFR, higher is better, but for creatinine and BUN, higher is a sign of damage. Urine tests are also used to check for albumin (alb-YOU-min), one of the proteins the kidneys are supposed to keep in the blood, not excrete. A microalbumin test can check for small (micro) amounts of albumin in your urine, which indicate kidney damage. These tests are usually done once a year for monitoring, or more often if DKD is progressing.
People with kidney disease are placed in stages 1 to 5, based on their eGFR results and clinical signs such as blood in the urine, swelling (edema) or damage visible on scans.
The eGFR is 90 or greater, a normal level, but there are other signs of DKD, such as microalbumin in the urine.
The eGFR is 60 to 89, but there are usually no physical symptoms. (For those with DKD, this is where you want to keep it.)
The eGFR is 30 to 59. This is where patients may start to feel sick with symptoms such as swelling or back pain, and they may develop anemia and/or high blood pressure. In stage 3, treatment and self-management recommendations change. Doctors will advise eating less protein, because protein breakdown products are hard on the kidneys. They may prescribe blood pressure medications to prevent heart failure.
The eGFR is 15 to 29, meaning the kidneys are severely damaged. At this stage, doctors will advise patients to start thinking about dialysis or a kidney transplant. (Some people may have a close relative willing to donate a kidney.)
The eGFR is less than 15, meaning a person has kidney failure. At this point, patients will need to go on dialysis or receive a kidney transplant. Both treatment options change a patient’s life and diabetes management.
From the self-management point of view, DKD could almost be considered as three separate conditions. Diets and medications are different in stages 3 to 4, on dialysis and after transplant. Here are some guidelines:
Focus on lowering glucose and blood pressure. Less carbohydrate and more protein and fiber may be recommended. Patients also need to limit salt and sodium intake. The National Kidney Foundation recommends the DASH (Dietary Approaches to Stop Hypertension) diet or a plant-based diet as the best options.
Patients must reduce protein to protect their kidneys from breakdown products. They also must reduce potassium and phosphorous and limit fluids, which sometimes means limiting fiber to avoid constipation.
Those on dialysis should eat lots of protein but tightly limit potassium, phosphorous and fluids (which should be kept below 32 ounces per day).
Food choices are less restricted, but be careful of weight gain from medicines and diet and of infection because immune systems are weakened by transplant drugs. Be sure to wash everything well.
For people with type 2 diabetes and chronic kidney disease, the American Diabetes Association’s Standards of Medical Care in Diabetes—2021 recommends providers consider prescribing drugs in the SGLT2 class (e.g. Invokana, Farxiga, Jardiance, Steglatro) or the GLP-1 inhibitor class (e.g. Trulicity, Victoza, Bydureon, Byetta, Adlyxin Ozempic, Rybelsus, Tanzeum). (People with type 1 diabetes require insulin to keep blood glucose levels in target range.) Some recent research suggests that metformin may be safe for certain people with mild kidney disease.
The American Association of Family Physicians advises physicians to prescribe blood pressure drugs in the angiotensin-converting enzyme (ACE) inhibitor class or the angiotensin receptor blocker (ARB) class for people with chronic kidney disease.
A few additional items to note regarding medications in people with kidney disease:
• According to DaVita Kidney Care, patients on dialysis often receive the blood-building drug erythropoietin, along with iron, to prevent anemia. They may also take phosphate binders with every meal to keep phosphorous levels down, along with a variety of vitamins.
• The Cleveland Clinic transplant center says that after a kidney transplant, patients need to take drugs such as steroids to protect the new kidney. These drugs can potentially affect diabetes management by increasing insulin resistance.
• Because kidneys play a major part in removing drugs from the body, kidney damage means drugs stay in the system longer. This means that doses of almost all medications will need to be adjusted by a physician for people with kidney disease.
• People with kidney failure, and especially those on dialysis, may have increased risk of hypoglycemia, or low blood glucose episodes that can have serious consequences. Patients should monitor glucose closely, using a continuous glucose monitor if possible.
• Patients with advanced DKD may not have much energy for exercise, but any gentle activity they can do will help with circulation and diabetes management. Walking, stretching and strengthening exercises are all good.
• Smoking damages blood vessels, so smoking with diabetes isn’t just a double whammy for kidneys — it’s the whammy squared. If you need help quitting smoking, visit Smokefree.gov.
Protecting your kidneys requires work, but it’s worth the effort. Regular screening, some lifestyle changes and medications, if necessary, can all ensure these organs stay in the best shape possible. As the Centers for Disease Control and Prevention (CDC) says, take care of your kidneys, and they will take care of you.
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