Creatinine vs Urea / BUN: what's the difference?
Educational — not medical advice · Ranges vary between laboratories
The short answer: Both are waste products the kidneys clear, but they come from different places. Creatinine comes from muscle at a steady rate, so it tracks filtration fairly consistently. BUN comes from protein breakdown, so diet, hydration, and even bleeding in the gut can move it while filtration stays the same.
Because muscles produce creatinine at a steady rate, a rising blood level means the kidneys are clearing less of it. Labs often pair it with eGFR, which converts creatinine into an estimated filtration rate.
Full Creatinine guideWhen your body breaks down protein, it produces urea as a waste byproduct, which the kidneys are supposed to filter out and send to the bladder. BUN measures how much of this waste is still circulating in your blood, making it one of the simplest windows into kidney filtering function.
Full Urea / BUN guideAt a glance
| Creatinine | Urea / BUN | |
|---|---|---|
| Panel | Kidney panel | Kidney panel |
| Unit | mg/dL | mg/dL |
| Typical adult range | Normal 0.6–1.2 mg/dL | Normal 7–20 mg/dL |
| Also known as | Serum Creatinine, Cr | Blood Urea Nitrogen, Serum Urea, Blood Urea |
General adult reference intervals — your lab's printed range takes precedence.
Why they're often tested together
Kidney panels report both because the pair helps separate a filtration problem from something else. A high BUN with a normal creatinine often points to dehydration, a high-protein diet, or gastrointestinal bleeding, while both rising together is more suggestive of reduced filtration. eGFR is usually reported alongside.
Questions people ask
Which one is more specific to the kidneys?
Creatinine, generally, because muscles produce it at a steady rate. It has its own confounders, though: high muscle mass and creatine supplements raise it without any kidney trouble, while low muscle mass can keep it deceptively low.
Why do some reports say urea and others BUN?
They measure the same waste product differently. BUN reports only the nitrogen portion of the urea molecule, while a urea value runs roughly 2.1 times higher. It's worth checking which one a report uses before comparing results over time.
More comparisons
One value tells half the story.
Upload your full report — every value checked and explained. Free — no account needed.