The Kidney-Diabetes Link: Progress in Saving Kidney Function!

By Dace Trence, MD, FACE

Remember feeling thirsty all the time? All those nights getting up to use the bathroom? And how that stopped as your blood sugars began to come down after you started treatment for your diabetes? The kidneys play a large role in diabetes- it is the only way the body can eliminate excess sugar (glucose). How well the kidneys can work over time can in turn be affected by high glucoses, as well as uncontrolled blood pressure and uncontrolled cholesterol, all part of having type 2 diabetes mellitus.

To keep the kidneys working as well as possible, kidney function needs to be monitored. Screening tests are typically recommended yearly from the time the diagnosis of Type 2 diabetes mellitus is made, usually started yearly after 5-10 years of type 1 diabetes mellitus. What is not well known is that if there are no kidney effects from diabetes in those with Type 1 diabetes after 25 years of the diabetes, then the risk of developing kidney complications decreases significantly. Unfortunately, this does not hold for those with the more common form of diabetes- Type 2- these individuals remain at risk for life.

Risk factors for developing diabetic kidney disease, include a family history of kidney function loss in those with diabetes (genetics), smoking, obesity, in addition to untreated high blood pressure and high cholesterol.

Screening tests for diabetic kidney disease usually start with checking for abnormal amount of protein in the urine. Healthy kidneys take wastes out of the blood, along with a small amount of protein that is eliminated in the urine. When kidneys start to work less well, increasing amounts of a protein called albumin may leak into the urine, a condition known as microalbuminuria. This can be checked for by a small urine sample obtained at any time of the day. Although this test is easy to do, it can frequently be falsely positive, so you should not panic if told that you have positive microalbuminuria or a positive microalbumin to creatinine ratio. Having a large steak dinner the night before, being on your feet for a prolonged period of time, having a urinary infection- these along with many other reasons, can give a positive microalbumin to creatinine test. You will usually be asked to confirm abnormal test results- either through another small urine sample or possibly a 24 hour urine collection. As kidney function worsens, the amount of albumin and other proteins in the urine increases, and the condition is called proteinuria. These are all measurements of the “leakiness” of the kidney.

The kidney also acts as an active filter of body wastes. GFR (glomerular filtration rate) is a calculation of how efficiently the kidneys are filtering wastes from the blood. The traditional GFR calculation required an injection into the bloodstream of a substance that was later measured in a 24-hour urine collection. We now calculate eGFR (estimated GFR) without an injection or urine collection, using only a blood measurement of creatinine and the person’s age, sex, and race. Many laboratories automatically calculate the eGFR when a creatinine value is measured and report it on the lab report. The National Kidney Foundation has determined different stages of chronic kidney disease based on the value of the eGFR. An eGFR of 90 or above is considered normal. Dialysis or transplantation is needed when the eGFR is less than 15.

Many steps can be taken if it is determined that you have diabetic kidney disease, to help protect remaining kidney function, even reverse early disease. High blood sugars should be brought under control. High blood pressure should be treated, starting with medications in the ACE (angiotensin converting enzyme) inhibitor or ARB (angiotensin receptor blocker) groups. High cholesterol should be treated, usually requiring a statin class drug. Some doctors tell their kidney patients to limit the amount of protein they eat so the kidneys have less work to do. But a person should not avoid protein entirely. You should work with a dietitian to create the right food plan for your needs, including limiting sodium (salt) which can raise the blood pressure, also limiting potassium as diseased kidneys may not be able to efficiently excrete excess potassium. High potassium levels can affect the heart rhythm. Smoking not only increases the risk of kidney disease, but it also contributes to deaths from strokes and heart attacks in those with kidney disease- so if you smoke, this is the time to quit!

The good news is that the incidence of kidney disease in people with diabetes is decreasing. This is thought to be related to increasing use of all the steps listed above, as soon as screening tests suggest that the kidneys are not working as well as they should. Talk to your diabetes specialist about your kidney tests and whether additional evaluation from a kidney specialist may be helpful, as people with diabetes can also have kidney disease from other causes than diabetes. Be involved in your health care and ask questions if any information is unclear!

Dr. Dace Trence is Director of the Diabetes Care Center and Associate Professor of Medicine at the University of Washington Medical Center in Seattle. She is also the University of Washington Endocrine Fellowship Program Director and Director of Endocrine Days, a medical education program for endocrinologists practicing in the Pacific Northwest. She is on the Board of Trustees for the American College of Endocrinology, chairs the AACE CME committee and is co-editor of Power of Prevention Magazine.