Creatinine Blood Test
The creatinine blood test measures a byproduct of normal muscle metabolism that the kidneys continuously filter out of the blood. Because production is fairly steady and removal depends on the kidneys, creatinine is one of the core markers associated with kidney function.
About this test
Muscles produce creatinine at a relatively constant rate as a byproduct of their everyday energy use, and the kidneys clear it from circulation around the clock. That steady-in, filtered-out arrangement is what makes the marker informative: when filtration slows, circulating creatinine tends to drift, and clinicians notice.
Creatinine is rarely read alone. It feeds into a calculated estimate of filtration (eGFR) that appears alongside it on most reports, and it is considered together with BUN, electrolytes, and the person's circumstances.
Who might consider this test?
- Creatinine is usually looked up after appearing on a routine panel, where it features almost universally.
- Interpretation belongs with a licensed clinician who knows your history.
Test details
| Quest code | 375 |
|---|---|
| Methodology | Spectrophotometry |
| Sample type | 1 mL serum |
| Collection | Quest patient service center |
Related tests and panels
Measures alkaline phosphatase, an enzyme related to liver, bile duct and certain…
Measures amylase, an enzyme from the pancreas and salivary glands associated…
Measures total bile acids, a marker used to evaluate liver function and bile flow.
Quest resources
Additional details
Why creatinine tracks with the kidneys
The logic is simple plumbing: production is steady, and the kidneys are the main exit. If the exit narrows, the level in circulation drifts. That is why creatinine — and the eGFR calculation built on top of it — anchors most kidney-associated laboratory assessment.
Muscle mass and other context
Because muscle produces creatinine, someone with substantially more or less muscle than average carries a different baseline. Recent heavy exercise, hydration, a large meat-heavy meal, and creatine supplements can each nudge results too — everyday context a clinician weighs before reading meaning into a change.
Creatinine, eGFR and BUN together
Most lab reports pair creatinine with an estimated filtration rate calculated from it, and with BUN, a second waste-product marker. The set is read as a group: agreement among them strengthens a story, and disagreement usually prompts a repeat or a closer look rather than a conclusion.
Ordering a creatinine test through Celio Health
Creatinine can be ordered individually or as part of the standard panels that almost always include it, with the physician order arranged automatically at purchase. Sample collection is a routine draw at a participating Quest Diagnostics patient service center, and results return securely as a PDF report, typically within a few business days.
People following kidney-associated markers over time often reorder the same panel at intervals their clinician suggests, so results stay comparable draw to draw.
Order online and a physician order is included — no doctor's visit and no insurance needed. Your sample is collected at a Quest Diagnostics patient service center.
Laboratory results should always be interpreted by a licensed clinician who knows your health history. This page is information about a test, not medical advice.
Frequently asked questions
What does creatinine measure?
A byproduct of normal muscle metabolism that the kidneys filter from the blood. Steady production plus kidney clearance makes it a core kidney-associated marker.
What is eGFR and how does it relate?
eGFR is an estimate of kidney filtration calculated from the creatinine result along with demographic factors. Most reports show the two together.
Can muscle or diet affect creatinine?
Yes. More muscle mass means more baseline production, and recent heavy exercise, meat-heavy meals or creatine supplements can nudge results — context a clinician considers.
Do I need to fast before a creatinine test?
Creatinine itself does not generally require fasting, but the panels it usually rides on sometimes do. Follow your requisition's instructions.
Can I get the Creatinine test without a doctor's visit or insurance?
Yes. The $15 cash price includes an independent physician's order, so no referral is needed, and insurance is never involved.