Creatinine

Also known as Cr, serum creatinine

C₄H₇N₃O small molecule

LOINC 2160-0 code verified serum mg/dL

unverified These explanations are written to be easy to read and have not yet been checked against a source. The ranges and measurement notes on this page show theirs.

definition unverified

A waste product your muscles make continuously. Healthy kidneys filter it out at a steady rate, so the amount left in your blood reflects how well they are filtering.

Non-enzymatic breakdown product of muscle creatine phosphate, produced at a rate proportional to muscle mass and cleared almost entirely by glomerular filtration.

why measured unverified

It is the standard way to check kidney filtering, mostly because production is steady and easy to account for.

No clinical version written yet.

if high unverified

Usually means the kidneys are filtering less than they should. Dehydration raises it temporarily. Being very muscular raises it without anything being wrong.

No clinical version written yet.

if low unverified

Usually just low muscle mass rather than a problem.

No clinical version written yet.

caveats unverified

Because it depends on muscle mass, the same number means different things in a heavily built athlete and a frail older person. That is exactly why the calculated eGFR exists, and why it is usually the better number to read.

No clinical version written yet.

What this substance is

formula: C₄H₇N₃O
mass: 113.12 g/mol
monoisotopic: 113.05891
charge: 0
InChIKey: DDRJAANPRJIHGJ-UHFFFAOYSA-N
ChEBI: CHEBI:16737
CAS: 60-27-5

Drawn from ChEBI's own curated 2D drawing, accepted only after its InChIKey, formula and charge matched the ChEBI release. Nothing here is hand-entered. Two masses are given because they answer different questions: the average is natural-abundance weighted and drives unit conversion; the monoisotopic value uses only the commonest isotope of each element and is what mass spectrometry measures.

3D model · Creatinine

Generated by RDKit from ChEBI's verified structure, and accepted only because its own 3D geometry reproduces ChEBI's InChIKey. A flexible molecule takes many shapes; this is one low-energy one. Drag to rotate, scroll to zoom.

Reference ranges

Checking your own result against this range needs the running application; this is a static copy. Nothing you type anywhere in Empeiria is ever sent to a server.

This open edition shows a range only where a public-domain or openly licensed source states one, and none does for this marker yet. Compare your result with the range printed on your own lab report.

How it is measured

In practice

For the blood test, a health worker takes a small blood sample from a vein in your arm. For the urine test, you may collect all your urine for 24 hours in a special container kept cold. You may be told not to eat meat for 24 hours before. Blood creatinine is often used to work out an estimated kidney filtering rate (eGFR).

Blood: serum, lithium heparin plasma or K2-EDTA plasma by venipuncture; urine is also acceptable, often as a refrigerated 24-hour collection because creatinine output varies through the day. Patients may be told to avoid meat for 24 hours, and to fast up to 12 hours if part of a BMP/CMP. Some drugs (rifampicin, levodopa, calcium dobesilate) give falsely low results. Serum creatinine is used to calculate eGFR, and paired blood and urine values give creatinine clearance.

Before the test

Do not eat meat for 24 hours before the test if your provider tells you to.
Fast (no food or drink) for up to 12 hours if creatinine is part of a BMP or CMP.
Tell your provider about all medicines and supplements you take, but do not stop any unless your provider tells you to.

Where: laboratory

Sources: Creatinine Test, MedlinePlus (U.S. National Library of Medicine); NHANES 2017-2018 Laboratory Procedure Manual, Creatinine (CDC National Center for Health Statistics) cited · not yet checked by a person

In the lab

enzymatic colorimetric

Enzymatic (creatininase cascade)

A chain of enzymes breaks the substance down. The last step produces a dye, and the depth of colour shows how much was there.

Creatininase, creatinase and sarcosine oxidase act in sequence to yield hydrogen peroxide, which reacts with a chromophore in a peroxidase-coupled step to give a coloured product.

Read by: Absorbance at 546 nm
Reference method: Isotope-dilution mass spectrometry
Standardised to: IDMS-traceable calibration

Isotope-labelled internal standard

d3-creatinine (creatinine carrying three deuterium atoms) is added as the internal standard in LC-MS/MS reference methods. It is chemically the same as creatinine but heavier, so the instrument can tell the two apart and use the standard to correct the measurement.

What can throw it off

Bilirubin
Haemolysis

Why labs disagree: This is the clearest example in the whole panel. The older Jaffe method also reacts with other substances in blood, including glucose, ketones and protein. In one comparison against a mass-spectrometry reference, Jaffe results averaged about 12% high while enzymatic results averaged about 2% low. So the two methods do not give the same number for the same blood, and a creatinine result should be judged against a range from the same kind of method.

Sources: LC-MS/MS Method for Serum Creatinine: Comparison with Enzymatic Method and Jaffe Method (PLoS One 2015), PMC open access; NHANES 2017-2018 Laboratory Procedure Manual: Creatinine (refrigerated serum), CDC/NCHS cited · not yet checked by a person

enzymatic colorimetric · less common

Jaffe kinetic alkaline picrate

An older method. The substance reacts with a chemical called picrate in an alkaline solution to give a red colour. Several other things in blood, such as glucose and ketones, react in a similar way.

Creatinine reacts with picrate under alkaline conditions to form a red complex; the rate of colour formation is read over a short, early time window (a kinetic or "rate" method).

Read by: Rate of absorbance change at 520 nm (Beckman DxC analyser used by NHANES)

What can throw it off

Glucose
Ketones
Protein
Cephalosporin antibiotics
Bilirubin

Sources: LC-MS/MS Method for Serum Creatinine: Comparison with Enzymatic Method and Jaffe Method (PLoS One 2015), PMC open access; NHANES 2015-2016 Laboratory Procedure Manual: Creatinine (Beckman DxC800, Jaffe), CDC/NCHS cited · not yet checked by a person

What it reports on

kidney cleared by
The kidneys filter creatinine out of the blood and remove it in urine, so it builds up when they fail.
renal glomerulus cleared by
The kidneys clear creatinine by filtering it, and that filtering is done mainly by the glomeruli.
skeletal muscle organ, vertebrate synthesized by
Creatinine is made when muscles are used and muscle tissue breaks down, so muscle mass sets how much is made.

Associated symptoms

When high

high Feeling tired all the time · non specific · common
high Swollen ankles or legs · suggestive · occasional
high Waking at night to urinate · suggestive · occasional
Loss of urinary concentrating ability disturbs the normal overnight reduction in urine output.
high Persistent itching · suggestive · occasional
Retained waste products in advanced kidney impairment.
high Loss of appetite · non specific · occasional

Conditions this marker features in

When high

high Sudden loss of kidney function · defining
KDIGO diagnostic criterion: serum creatinine up by at least 0.3 mg/dL within 48 hours, or to at least 1.5 times baseline within 7 days. Stage 3 includes 3 times baseline or a level of 4.0 mg/dL or more.
high High blood sodium · supportive
Part of the standard work-up. A raised creatinine can point to dehydration as the cause.
high Long-term reduced kidney function · supportive
Used to calculate eGFR, which is what the CKD definition uses. Creatinine rises as kidney disease gets worse.

Ordered as part of

cmp · bmp · renal