Markers explained
Creatinine and BUN: The Kidney Test, in Plain Words
Creatinine and blood urea nitrogen are two waste checks often included in a metabolic panel. A higher number is a reason to look closer, not a diagnosis.
Healiam·October 16, 2026·2 min read
Kidneys are two organs, each about the size of a fist. Together they filter about half a cup of blood every minute — on the order of 150 quarts a day — and send about 1–2 quarts out as urine. They remove wastes and extra water, balance salts and minerals, help control blood pressure, and help make red blood cells. Each kidney has about a million tiny filters called nephrons.
Two blood markers often stand in for that work: creatinine and BUN (blood urea nitrogen). They are frequently part of a basic or comprehensive metabolic panel, and both are on the Healiam kidney group.
Creatinine
The muscle-waste check
Mayo Clinic typical ranges: women 0.59–1.04 mg/dL, men 0.74–1.35 mg/dL. Labs differ — read the range on your report.
Higher
May point to kidney disease or injury.
Lower
May reflect low muscle mass or malnutrition.
BUN
The protein-waste check
A commonly cited adult range is about 7–20 mg/dL. It usually rises with age and varies by lab.
Higher
Can mean the kidneys aren’t clearing waste well. It can also come from dehydration, a high-protein diet, some medicines, burns, or a recent heart attack.
Lower
Can come from low protein intake, malnutrition, or liver disease.
How the two wastes get there
Working muscle breaks down and releases creatinine, a normal waste, into the blood. Healthy kidneys filter it into urine. Separately, the body breaks protein down into urea nitrogen, which travels in the blood until the kidneys remove it.
What can nudge the numbers
- Hydration. Dehydration can raise BUN.
- Meat and protein. What you eat can shift results. A clinician may ask you to avoid meat for 24 hours beforehand.
- Muscle mass. Creatinine comes from muscle.
- Hard exercise. Intense workouts can nudge results.
- Age. BUN usually rises with age.
- Medicines and supplements. Tell your clinician what you take, and keep taking them unless you are told otherwise.
People with diabetes, high blood pressure, or heart disease may be checked more often. If these markers are bundled with other tests, you may be asked to fast — Healiam’s panel asks for 8–12 hours. A BUN test on its own usually needs no special prep.
1 in 10
More than 1 in 10 U.S. adults is estimated to have chronic kidney disease
9 in 10
About 9 in 10 of them did not know they had it
One reading
The CDC estimate uses a single measurement, so it may overstate prevalence
Sources
- NIDDK — Your Kidneys & How They Work
- MedlinePlus — Creatinine Test
- MedlinePlus — BUN (Blood Urea Nitrogen)
- Mayo Clinic — Creatinine and BUN reference ranges, as cited in Healiam Markers Explained 03
- CDC — Chronic kidney disease estimate, NHANES August 2021–August 2023
This article is for educational purposes and does not provide medical advice, diagnosis, or treatment. Results should be interpreted in the context of your individual health and, when appropriate, discussed with a licensed healthcare professional. Healiam testing and result delivery do not replace professional medical advice, diagnosis, or treatment.