Lab test, explained · Reviewed by the Medical Records Vault clinical team · Last reviewed June 2026
What is creatinine? Your kidney test, explained
Creatinine is a waste product from normal muscle activity that healthy kidneys filter out of the blood. A blood creatinine test estimates how well your kidneys are clearing it. Higher-than-expected creatinine can suggest the kidneys are filtering less efficiently, but levels vary with muscle mass, hydration, and age.
- Measures
- A muscle waste product the kidneys filter out
- Higher may suggest
- Kidneys filtering less efficiently
- Also affected by
- Muscle mass, hydration, age, some medicines
What it tells you about your kidneys
Your muscles produce creatinine continuously as a waste product, and healthy kidneys filter it out of the blood at a steady rate. So the amount left in the blood is a useful indirect measure of how well the kidneys are filtering. It is often reported with eGFR, an estimate of kidney filtering capacity calculated from creatinine, age, and sex.
What can move the number
A higher-than-expected creatinine can suggest the kidneys are filtering less efficiently, but the value is also affected by muscle mass, dehydration, and some medicines. Doctors usually look at the trend over time and the eGFR rather than a single reading.
Questions to ask your doctor
Bring these to your next visit. They are written to help you understand what was already decided — not to second-guess your doctor.
- 1.What is my creatinine and my eGFR (the related kidney-function estimate)?
- 2.Could hydration or a medicine be affecting this result?
- 3.Does this need repeating to see a trend?
Common questions
- What does high creatinine mean?
- Raised creatinine can suggest the kidneys are filtering blood less efficiently, but it is also influenced by muscle mass, dehydration, and certain medicines. Doctors usually read it together with eGFR and a trend over time rather than from one value.
This is an educational explanation, not a diagnosis or medical advice. Medical Records Vault explains what documents say and what is commonly done; it never tells you what you have or what to change. Always consult your doctor for any medical decision.
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