Creatinine

Labs & Biomarkers · Reviewed August 2026

Definition

Creatinine is a waste product formed when creatine, an energy-storage compound in muscle, breaks down.[1] The body makes it at a fairly steady rate, and the kidneys filter it out of the blood, so a serum creatinine test is a standard part of routine bloodwork and kidney function estimates.[2]

Educational content, not medical advice. For personal or fertility concerns, please consult your doctor.

What Creatinine Measures

Skeletal muscle stores energy as creatine phosphate, and creatinine is the breakdown product left over as that store turns over. The body produces it at a fairly constant rate, and how much a person makes depends on their muscle mass.[1] The kidneys do the clearing. The glomerulus, the kidney's filtering unit, filters creatinine freely out of the blood, and under steady conditions the amount leaving in urine matches the amount muscle produces.[1]

That pairing of steady production with kidney clearance is why creatinine is the standard measured input for estimating how fast the kidneys filter blood: the 2021 CKD-EPI equations calculate eGFR from a serum creatinine result combined with age and sex.[5]

How It's Measured

Serum creatinine comes from a standard blood draw and is usually reported in milligrams per deciliter. It's rarely ordered alone, appearing instead as one line on the basic metabolic panel or the comprehensive metabolic panel, two of the most common routine blood test groups.[2] Creatinine can also be measured in urine, where testing uses it as a concentration marker in results like the urine albumin-to-creatinine ratio.[2]

Why People Track Creatinine

Creatinine shows up on nearly every routine blood panel, so anyone who collects their lab results ends up with a creatinine history whether they set out to build one or not. It also isn't a kidney-only number. Production tracks muscle mass and can shift with what you ate before the draw, which is a reason to keep the date and context attached to each result instead of reading any one number in isolation.[3],[4]

How Go Go Gaia Tracks Creatinine

Go Go Gaia doesn't draw blood or run labs. You upload a creatinine result from bloodwork you've already had done, and the app stores it as a dated data point and charts it over time next to related values like BUN and eGFR. The lab list also includes urine creatinine and the urine albumin-to-creatinine ratio as their own entries, so a urinalysis result lands in the same timeline as your blood panels.

Keep every blood panel in one timeline

Upload creatinine and the rest of your lab results, then see them charted over time next to your cycle, symptoms, and habits.

Get Go Go Gaia

Free to download on the App Store.

What the Research Shows

Muscle mass shapes creatinine independent of kidney function. In a 2008 study of healthy adults, lean mass stayed significantly related to serum and urinary creatinine even after the researchers adjusted for protein and meat intake.[3]

Diet moves it too, at least briefly. In a 2007 study, a cooked meat meal raised participants' median serum creatinine one to two hours after eating, enough to shift the eGFR calculated from it.[4]

Because average creatinine differs across people in ways unrelated to filtration, the standard estimating equations never read the number alone. The 2021 CKD-EPI equations combine serum creatinine with age and sex, and their 2021 revision removed race as a variable.[5]

Related Terms

eGFR

The filtration estimate calculated from a creatinine result plus age and sex.

BUN

Blood urea nitrogen, the other kidney-related value on a basic metabolic panel.

Ferritin

Another blood-panel value tracked as an uploaded lab result and charted over time.

Frequently Asked Questions

Educational information based on published sources. Not medical advice. For personal concerns, please consult your doctor.

Does Go Go Gaia run creatinine blood tests?

No. Go Go Gaia doesn't draw blood or run labs. You get a creatinine result from bloodwork ordered through a clinician or lab service, then upload it to your Go Go Gaia account so it's stored and charted alongside your other tracked data.

What's the difference between creatinine and eGFR?

Creatinine is the value a lab actually measures in blood. eGFR is a number calculated from that creatinine result together with age and sex, using standard equations, to estimate how fast the kidneys filter blood. One is a measurement, the other is a calculation built on top of it.

Why does creatinine show up on urine tests too?

Creatinine can be measured in urine as well as blood. Urine testing uses it as a concentration marker, and some results are reported as ratios, like the urine albumin-to-creatinine ratio. Go Go Gaia stores urine creatinine and that ratio as their own lab types, separate from serum creatinine.

References

  1. Shahbaz H, Rout P, Gupta M. Creatinine Clearance. StatPearls. NCBI Bookshelf. NBK544228
  2. MedlinePlus. Creatinine Test. National Library of Medicine (US). medlineplus.gov
  3. Baxmann AC, Ahmed MS, Marques NC, et al. Influence of muscle mass and physical activity on serum and urinary creatinine and serum cystatin C. Clinical Journal of the American Society of Nephrology. 2008;3(2):348-354. DOI: 10.2215/CJN.02870707
  4. Preiss DJ, Godber IM, Lamb EJ, Dalton RN, Gunn IR. The influence of a cooked-meat meal on estimated glomerular filtration rate. Annals of Clinical Biochemistry. 2007;44(Pt 1):35-42. DOI: 10.1258/000456307779595995
  5. Inker LA, Eneanya ND, Coresh J, et al. New creatinine- and cystatin C-based equations to estimate GFR without race. New England Journal of Medicine. 2021;385(19):1737-1749. DOI: 10.1056/NEJMoa2102953

Sourced from peer-reviewed research and, for basic mechanism claims, established references like NIH and StatPearls. Every citation above is checked to confirm it resolves to a real source and supports the sentence it's attached to. Last reviewed August 2026. See our full methodology on the Encyclopedia hub.