5 minute read

Published January 17, 2026

Your kidneys may be relatively small, but they have big responsibilities. Every day, they work quietly around the clock to keep your body in balance and running smoothly. But when kidney health changes, the signs aren’t always obvious.¹,²

What do the kidneys do?

Your kidneys do many important jobs, but their primary role is to filter your blood. Each day, they move about 200 quarts of fluid through their filters to remove waste products, toxins, and excess fluid. Most of this fluid is cleaned and returned to circulation, with only a small amount leaving the body as urine. Without this steady filtration, waste would build up in the bloodstream and begin affecting the entire body.¹,²

Beyond clearing waste, the kidneys also help¹

  • Maintain fluid and electrolyte balance
  • Regulate blood pressure
  • Support red blood cell production
  • Activate vitamin D
  • Regulate the pH (acid-base balance) of the blood
  • Produce small amounts of glucose (sugar) when needed

Why kidney health matters

Your kidneys are essential for keeping your entire body in balance. By continuously filtering blood and managing fluid levels and blood chemistry, they help maintain the stability your body relies on to function at its best.

When kidney function declines, that balance can begin to shift. Blood pressure may rise, anemia could develop, and blood chemistry can be disrupted. Because the kidneys are highly adaptable, these changes often happen slowly and without obvious symptoms. That’s why chronic kidney disease often goes unnoticed until it’s more advanced and why early detection matters.²

 

What are albumin, creatinine, cystatin C, and eGFR? What can they tell me about kidney health?

Albumin is a protein made by the liver and the main protein found in the blood. The kidneys keep substances the body needs, like albumin, in the bloodstream while filtering out waste. When the kidneys are damaged, albumin can leak into the urine, where it doesn’t belong. Albumin in the urine can be an early sign of kidney disease.⁴

Creatinine is a waste product created by muscles during normal activity. The kidneys filter creatinine out of the blood and remove it through urine. When kidney function decreases, creatinine can build up in the blood. The amount of creatinine in the blood reflects how well the kidneys remove waste.⁴

Cystatin C is a protein produced by cells throughout the body and removed from the blood by the kidneys. Like creatinine, higher levels of cystatin C in the blood can indicate reduced kidney function. Because cystatin C is less affected by muscle mass, age, and diet, it can provide additional insight into kidney health.⁵

Estimated glomerular filtration rate, or eGFR, is an estimate of how well the kidneys filter blood. It’s calculated using the levels of creatinine, cystatin C, or both, along with factors such as age and sex. eGFR is used to evaluate overall kidney function.⁵

When the kidneys don’t function as they should, waste products, toxins, and excess fluid can build up in the blood and affect the body in ways such as⁵,⁷

  • High blood pressure
  • Changes in urination (going more or less often than usual)
  • Foamy or bubbly urine
  • Swelling in the arms, hands, legs, ankles, or feet (edema)
  • Puffiness around the eyes
  • Feeling tired or weak
  • Trouble concentrating
  • Loss of appetite
  • Nausea or vomiting
  • Muscle cramps or aches
  • Dry or itchy skin
  • Trouble sleeping
  • Shortness of breath 

CKD can progress slowly and without obvious symptoms. If something feels off, talk with your doctor.

What causes chronic kidney disease (CKD)?

For many people, there’s usually no single cause. CKD often develops over time from a combination of factors or health conditions that damage the kidneys. Anyone at any age can develop CKD, and some people are at a higher risk than others.⁵

Common CKD risk factors⁵,⁷

  • Diabetes
  • High blood pressure
  • Heart disease
  • Family history of kidney disease
  • Personal history of kidney injury
  • Age 60 or older
  • Smoking or using tobacco products
  • Long-term use of certain pain medications

CKD may also develop due to other health conditions that affect the kidneys or block urine flow, such as⁶,⁸

  • Lupus
  • Kidney cancer
  • Kidney stones
  • Hepatitis C
  • Repeated or long-lasting kidney infections
  • Frequent, untreated, or long-lasting urinary tract infections (UTIs)

 

What are the stages of CKD?

CKD is commonly grouped into 5 stages based on how well the kidneys filter waste from the blood. Blood and urine tests help doctors determine the stage of CKD.⁷,⁹,¹⁰

Stage 1 CKD 90 or higher eGFR/mL/min (for 3 months or more): Normal kidney function with signs of mild kidney damage
Stage 2 CKD 60-89 eGFR/mL/min (for 3 months or more): Normal kidney function with more signs of mild kidney damage
Stage 3a CKD 45-59 eGFR/mL/min (for 3 months or more): Mild to moderate loss of kidney function
Stage 3b CKD 30-44 eGFR/mL/min (for 3 months or more): Moderate to severe loss of kidney function
Stage 4 CKD 15-29 eGFR/mL/min (for 3 months or more): Severe loss of kidney function
Stage 5 CKD Less than 15 eGFR/mL/min (for 3 months or more): Very severe loss of kidney function (kidney failure). The kidneys are no longer able to meet the body’s needs
 

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References

1.    Cleveland Clinic. Kidney. Accessed December 23, 2025. https://my.clevelandclinic.org/health/body/21824-kidney

2.    National Kidney Foundation. Chronic kidney disease (CKD). Updated September 11, 2023. Accessed December 23, 2025. https://www.kidney.org/kidney-topics/chronic-kidney-disease-ckd

3.    Centers for Disease Control and Prevention (CDC). Chronic kidney disease in the United States, 2023. Updated May 18, 2024. Accessed December 23, 2025.

https://www.cdc.gov/kidney-disease/php/data-research/index.html

4.    National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). Chronic kidney disease tests and diagnosis. Accessed December 23, 2025. https://www.niddk.nih.gov/health-information/kidney-disease/chronic-kidney-disease-ckd/tests-diagnosis

5.    National Kidney Foundation. Chronic kidney disease (CKD). Accessed December 23, 2025. https://www.kidney.org/kidney-topics/chronic-kidney-disease-ckd

6.    American Kidney Fund. Types of kidney diseases. Accessed December 23, 2025. https://www.kidneyfund.org/all-about-kidneys/types-kidney-diseases

7.    Cleveland Clinic. Chronic kidney disease. Accessed December 23, 2025. https://my.clevelandclinic.org/health/diseases/15096-chronic-kidney-disease

8.    American Kidney Fund. Other kidney problems. Accessed December 23, 2025. https://www.kidneyfund.org/all-about-kidneys/other-kidney-problems

9.    Kidney Disease: Improving Global Outcomes (KDIGO) CKD Work Group. KDIGO 2024 clinical practice guideline for the evaluation and management of chronic kidney disease. Kidney Int. 2024;105(4S):S117-S314. doi:10.1016/j.kint.2023.10.018

10. National Kidney Foundation. Stages of chronic kidney disease (CKD). Accessed December 23, 2025. https://www.kidney.org/kidney-topics/stages-chronic-kidney-disease-ckd