Educational Content Only This article provides general health information and is not medical advice. Always consult with your healthcare provider about your individual screening needs and any concerns about your kidney health.
Your kidneys work around the clock filtering waste from your blood, regulating blood pressure, balancing fluids and electrolytes, and producing hormones that support bone health and red blood cell production. When kidneys aren't functioning properly, problems can develop gradually and without obvious symptoms.
Kidney function tests help detect problems early, when treatment is most effective. Understanding these simple blood tests can help you monitor one of your body's most vital filtration systems.
The Two Key Kidney Function Tests
Creatinine
Creatinine is a waste product produced by your muscles during normal activity. Your kidneys filter creatinine out of your blood and eliminate it through urine. When kidneys aren't working properly, creatinine builds up in your bloodstream.
A simple blood test measures your serum creatinine level. While this number alone provides useful information, healthcare providers typically use it to calculate another important measure: your estimated glomerular filtration rate (eGFR).
Normal creatinine ranges:
- Men: 0.74-1.35 mg/dL
- Women: 0.59-1.04 mg/dL
Higher creatinine levels can indicate reduced kidney function, though it's important to note that levels can vary based on age, muscle mass, and other factors.
eGFR (Estimated Glomerular Filtration Rate)
Your eGFR is considered the best overall measure of kidney function. It estimates how much blood your kidneys filter each minute. The calculation uses your creatinine level along with your age, sex, and sometimes race to estimate how well your kidneys are working.
What the results mean:
- 90 or higher: Normal kidney function (if no other signs of kidney damage)
- 60-89: Mild decrease in kidney function (may be normal for older adults)
- 45-59: Mild to moderate decrease in kidney function
- 30-44: Moderate to severe decrease in kidney function
- 15-29: Severe decrease in kidney function
- Less than 15: Kidney failure (dialysis or transplant may be needed)
An eGFR below 60 for three months or more indicates chronic kidney disease (CKD). However, one low result doesn't necessarily mean you have kidney disease—your healthcare provider will retest to confirm.
Understanding Chronic Kidney Disease
Chronic kidney disease affects approximately 37 million American adults, yet about 90% of people with early-stage CKD don't know they have it. The condition develops gradually, often over many years, which is why regular screening is so important for people at risk.
CKD is divided into stages based on eGFR and other factors. Early stages (1-2) often have no symptoms and may only be detected through testing. As kidney function declines, symptoms might include fatigue, swelling in legs and ankles, changes in urination, difficulty concentrating, poor appetite, and trouble sleeping.
The good news: catching kidney disease early allows for interventions that can slow or even stop its progression. Many people with early-stage CKD never progress to kidney failure when they receive appropriate treatment and make necessary lifestyle changes.
Who Should Get Kidney Function Testing
Regular kidney function screening is particularly important if you have:
- Diabetes—the leading cause of kidney disease
- High blood pressure—the second leading cause
- Heart disease
- A family history of kidney disease
- Age 60 or older
- Obesity
- A history of acute kidney injury
- Long-term use of medications that can affect kidneys (like NSAIDs)
If you have diabetes or high blood pressure, your healthcare provider will likely check your kidney function at least annually. For others without risk factors, kidney function is often checked as part of routine blood work during annual physicals.
Additional Kidney Tests
Beyond creatinine and eGFR, your healthcare provider might order additional tests to evaluate kidney health:
Urine Albumin Test: This test checks for protein in your urine, which can be an early sign of kidney damage. Healthy kidneys don't let significant amounts of protein leak into urine.
BUN (Blood Urea Nitrogen): Like creatinine, urea is a waste product your kidneys should filter out. Elevated BUN can indicate reduced kidney function, though it's also affected by diet and hydration.
Together, these tests provide a comprehensive picture of how well your kidneys are working and whether any early damage has occurred.
What Affects Your Results
Several factors can influence kidney function test results:
- Muscle mass: People with more muscle mass naturally have higher creatinine levels
- Diet: High-protein diets can temporarily increase BUN levels
- Hydration: Dehydration can affect both creatinine and BUN levels
- Medications: Certain drugs can impact kidney function or test results
- Age: Kidney function naturally declines with age, which is factored into eGFR calculations
- Intense exercise: Can temporarily raise creatinine levels
This is why your healthcare provider considers the complete picture—your medical history, symptoms, and trends over time—rather than relying on a single test result.
What to Do If Results Are Abnormal
If your kidney function tests show abnormalities, your healthcare provider will likely:
- Repeat the tests to confirm results
- Order additional tests, including urine tests
- Review your medications and adjust if needed
- Refer you to a nephrologist (kidney specialist) if necessary
- Develop a treatment plan to protect your remaining kidney function
Treatment often focuses on managing underlying conditions like diabetes and high blood pressure, making dietary changes, and monitoring kidney function regularly. The goal is to slow disease progression and prevent complications.
Questions to Ask Your Healthcare Provider
When discussing kidney function tests, consider asking:
- What are my creatinine and eGFR numbers specifically?
- How do my results compare to previous tests?
- Given my risk factors, how often should I have kidney function testing?
- Are any of my medications affecting my kidney function?
- What lifestyle changes can I make to protect my kidney health?
- Do I need any additional kidney tests?
The Bottom Line
Kidney function tests are simple, routine blood tests that provide crucial information about your kidney health. Because chronic kidney disease often develops silently, regular screening is the best way to catch problems early and take action to protect your kidneys.
If you have diabetes, high blood pressure, or other risk factors, make sure kidney function testing is part of your regular healthcare routine. Early detection combined with proper management can help keep your kidneys healthy for years to come.
Take Action: If you haven't had your kidney function checked and you have risk factors, talk to your healthcare provider about getting tested. Know your numbers—particularly your eGFR—and track them over time to monitor trends in your kidney health.