Kidney disease is stealthy. It can stalk its victims without symptoms. In the United States, one-third of adults are at risk. Across the world, it affects more people in India and China than elsewhere. Women are more susceptible than men. Kidney disease cases have risen by nearly 30% since 1990. It can affect people of all ages and fitness levels. Because of this, the only way to be certain your kidneys are performing optimally is to schedule a doctor’s appointment and undergo tests for kidney function. So what are they and how do you prepare for them? Even more importantly, are there ways to prevent kidney disease?
Located just below your ribs, this pair of fist-sized and bean-shaped organs mainly work as your body’s filtration system. By filtering around half-a-cup of blood every minute, they extract extra fluid, acid, and wastes products generated by other cells. When they are working properly, they maintain a healthy balance of water, salts, and minerals. Because they convert Vitamin D from the sun or supplements to the form your body uses, improperly working kidneys can contribute to Vitamin D deficiency. As people have increasingly worked indoors, the amount of sunlight they are absorbing has decreased. Vitamin D deficiency has similarly increased––especially among people of color. Recent studies suggest that Black people in particular with higher levels of the vitamin may have a lower risk of contracting COVID-19. This is also a group with a higher risk for kidney disease.
Improperly working kidneys also produce less of a hormone called erythropoietin (EPO) that signals your bone marrow to produce red blood cells. When production of red blood cells drops, less oxygen is delivered to your tissues and organs. They also help keep your blood pressure in check by eliminating waste products and excess water. With all the kidneys do, it’s important to make sure they are healthy. That’s why testing and early detection of kidney disease is so important.
When you are tested, your doctor will be looking at your estimated glomerular filtration rate (eGFR)––which reveals how fast your kidneys filter waste products. Because your kidneys filter protein, detecting protein it in your urine is a key indicator of kidney disease.
Often used as a performance enhancing supplement, creatinine (like protein) is generally considered safe. Studies also suggest it can speed recovery time and reduce damage to muscles. However, like protein, its presence in the urine is another sign that your kidneys aren’t functioning properly. That’s why your doctor may ask for a 24-hour urine sample. After awakening and urinating as you normally would into a toilet, you will spend the next day collecting and storing your urine in a special container. While it’s definitely a bit nasty (and you want to make sure it’s labeled and not stored by the apple juice in your refrigerator!), it allows your doctor to perform a creatinine clearance test to determine how efficiently your kidneys are removing the chemical compound.
Your blood can be tested to determine presence of creatinine (normal 0.6 to 1.3) and BUN (normal 7 to 20), along with other factors, these numbers can be used to calculate your eGFR. The eGFR can be used to determine what stage of kidney disease you have.
The most accurate way to determine your kidney function is to perform a 24-hour urine sample. After awakening and urinating as you normally would into a toilet, you will spend the next day collecting and storing your urine in a special container, which has to stay cold. While it’s definitely a bit nasty (and you want to make sure it’s labeled and not stored by the apple juice in your refrigerator!), it allows your doctor to perform a creatinine clearance test to determine how efficiently your kidneys are removing waste and toxins.
Other tests include an ultrasound of the kidneys, which will tell the shape and health of the organ. Also, some kidney doctors may offer a kidney biopsy, where a small needle is inserted through the back into a kidney. Then a sample of kidney tissue is removed and examined under a microscope.
These tests can detect stage one kidney disease, when the organs are working but not at their optimal level. The goal is to avoid total kidney failure. Drinking lots of water instead of soda or fruit juice is a great way to reduce kidney stones and improve your health, as is reducing your sodium intake and eating more fresh fruits and vegetables. Finally, be sure to include a kidney function test in your next check-up.
Written by John Bankston
- Know Your Kidney Numbers: Two Simple Tests
- The impact of chronic kidney disease on global health
- Your Kidneys & How They Work
- Vitamin D: The Kidney Vitamin?
- CDC’s Second Nutrition Report: Vitamin D deficiency closely related to race and ethnicity
- Study suggests high vitamin D levels may protect against COVID-19, especially for Black people
- Anemia in Chronic Kidney Disease
- You and Your Hormones: Kidneys
- Creatine Use in Sports
- International Society of Sports Nutrition position stand: safety and efficacy of creatine supplementation in exercise, sport, and medicine
- Tests to Measure Kidney Function, Damage and Detect Abnormalities
- 6 Easy Ways to Prevent Kidney Stones
John Bankston is a published author of over 150 nonfiction books for children and young adults including biographies of Jonas Salk, Gerhard Domak, and Frederick Banting.