Creatinine and BUN Testing: What These Kidney Markers Show

What creatinine measures

Creatinine is a waste product made by muscles during normal activity. The kidneys filter it from the blood, and healthy kidneys remove most of it. A blood creatinine level can rise when kidney filtering slows, which is why it is one of the core markers of kidney function. Muscle mass, diet, and some medicines can also influence the level, so a clinician reads it in context rather than as a standalone answer.

Creatinine is also measured in urine, most often as part of a collection or a ratio with protein, to help assess how the kidneys are working over a period of time rather than at a single moment.

What BUN measures

Blood urea nitrogen (BUN) measures the amount of nitrogen in the blood that comes from urea, a waste product the liver makes when it breaks down protein. The kidneys remove urea, so BUN can rise when kidney function falls or when the body produces more urea than usual. Dehydration, a high-protein diet, bleeding in the digestive tract, and some medicines can also push BUN up, which is why it is interpreted alongside creatinine rather than alone.

Creatinine and BUN together: the ratio

Laboratories often report a BUN-to-creatinine ratio, a single number calculated from the two results. The ratio can help a clinician tell apart different causes of abnormal values. For example, a high ratio with a rising BUN can occur with dehydration or reduced blood flow to the kidneys, while both values rising together can reflect a problem with the kidneys themselves. The ratio is a clue, not a diagnosis, and it is always read with the full clinical picture, including your history and any symptoms.

When both markers are normal but symptoms persist, a clinician may still order further testing, because these two values do not capture every aspect of kidney health. Urine tests that check for protein or albumin often add information that blood markers alone cannot provide, and they can help confirm what the blood results suggest.

If you are monitoring a known condition, repeating the same panel at the same lab makes trends easier to read than comparing values across different labs and formulas.

What can affect the numbers

Many factors move creatinine and BUN up or down without any kidney disease. Muscle mass affects creatinine, so people with more muscle often run higher, and those with less muscle often run lower. Hydration, protein intake, recent intense exercise, pregnancy, and certain medicines can all shift the values. Because of this, reference ranges are broad and a single out-of-range result does not automatically mean something is wrong. A clinician may repeat the test or add a urine test to clarify what is going on.

Who may need these tests

Creatinine and BUN are commonly ordered as part of a basic or comprehensive metabolic panel. They may be checked during routine visits, before and after starting medicines that can affect the kidneys, when monitoring a long-term condition such as diabetes or high blood pressure, or when someone has symptoms such as swelling, fatigue, or changes in urination. People with a family history of kidney disease may also be tested periodically to track their baseline over time.

How to order / where to get tested

You can order creatinine and BUN testing through a self-pay lab service or have it ordered by a clinician. Self-pay testing is simple: choose a kidney function panel online, pay the listed price, and visit a CLIA-certified lab near you for the blood draw. Most self-pay kidney panels do not require fasting, and no doctor referral is needed for most orders. Results arrive in a secure online portal, often within a few business days. Share any flagged values with a licensed clinician who can interpret them with your history and decide whether more testing is useful.

How much does it cost

Creatinine and BUN are inexpensive tests on their own and are often bundled into a basic or comprehensive metabolic panel. A standalone kidney function panel typically costs less than a broad wellness package because it covers fewer markers. Because self-pay prices are set by the lab, the amount shown at checkout is generally the final amount. Insurance may cover these tests when a clinician orders them and you meet coverage rules. Comparing the current price on each panel page is the easiest way to choose the option that fits your budget.