Laboratory test · Sport and fitness
Creatinine (serum or urine)
- Sample: venous blood or urine
- Preparation: no meat for 12 h; fasting not essential
Test price
- Sample
- venous blood or urine
- Preparation
- no meat for 12 h; fasting not essential
Paymentcash, cards and instalments
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Creatinine is a waste product of muscle activity that the kidneys remove from the body. Blood creatinine is a basic test for assessing kidney function: together with age and sex, it is used to calculate estimated glomerular filtration rate (eGFR). Creatinine can also be measured in urine.
Who the test is for
- people having a general or preventive check-up, alongside urea and urinalysis;
- people with diabetes, high blood pressure, heart disease or chronic kidney disease, for regular monitoring;
- people taking medicines that may burden the kidneys or whose dose depends on kidney function;
- people with swelling, changes in urination, vomiting, diarrhoea or dehydration;
- people having a contrast-enhanced CT or MRI scan or certain procedures.
What creatinine is and what it indicates
Most creatine in the body is found in muscles, where it acts as a rapid energy reserve. A small amount breaks down into creatinine each day, travels through the blood to the kidneys and is excreted in urine. The less effectively the kidneys filter blood, the more blood creatinine rises.
Creatinine levels also depend on muscle mass: men and athletes have more, while older, smaller people and those with little muscle have less. Creatinine alone is therefore not a perfect measure. It can remain within the reference interval even when kidney filtration is already significantly reduced, particularly in older people. That is why eGFR is calculated alongside it.
Creatinine and eGFR
eGFR estimates how many millilitres of blood the kidneys filter per minute, adjusted to an average body size (mL/min/1,73 m²). In adults it is calculated from creatinine, age and sex, most often using the CKD-EPI equation. Categories according to international KDIGO guidelines:
| eGFR (mL/min/1,73 m²) | Meaning |
|---|---|
| 90 and above | normal filtration |
| 60–89 | mildly reduced, common in older age |
| 45–59 | mildly to moderately reduced |
| 30–44 | moderately to severely reduced |
| 15–29 | severely reduced |
| below 15 | kidney failure |
One result is not a diagnosis. Chronic kidney disease is defined by eGFR below 60 or other signs of kidney damage, such as protein in urine, lasting longer than three months. eGFR is less reliable with very high or very low muscle mass and during pregnancy; a doctor may then request creatinine clearance from 24-hour urine.
Panels including this test
Test Creatinine (serum or urine) is also included in these panels.
Preparation and sample
Creatinine is most often measured in venous blood. You do not need to fast unless other tests that day require it, such as glucose or lipids. Under British NICE guidelines, avoid meat for 12 hours before sampling because cooked meat temporarily raises creatinine. Avoid strenuous exercise the day before and drink water as usual. If you take creatine supplements, tell your doctor, because they can raise creatinine without kidney damage.
Urine creatinine is measured in a single sample or urine collected over 24 hours, depending on what the doctor requests. It most often serves as a comparison value for other urine tests or to calculate clearance.
How results are interpreted
Creatinine is expressed in µmol/L, and blood creatinine reports also include eGFR. The reference interval depends on sex, age and method and is printed on the report. A doctor interprets it alongside eGFR, urea, urinalysis and previous results, because changes over time also matter.
High creatinine
- Reduced kidney function: chronic kidney disease, most often associated with diabetes and high blood pressure, or sudden, acute kidney injury.
- Dehydration and reduced blood flow through the kidneys, for example after vomiting and diarrhoea or in heart failure.
- Obstructed urine flow, for example due to an enlarged prostate or stone.
- Temporary causes that do not mean kidney disease: a large meat meal, strenuous exercise, creatine supplements, high muscle mass and certain medicines.
A sudden rise in creatinine, particularly with reduced urination, swelling or marked weakness, requires medical assessment without delay.
Low creatinine
Low creatinine most often means lower muscle mass, for example in older age, malnutrition or muscle disease. It is also lower during pregnancy, when the kidneys filter more blood. By itself, it is rarely a cause for concern.
Creatinine before contrast-enhanced CT or MRI
Intravenous contrast agents are excreted through the kidneys, so the imaging facility usually requests recent creatinine results with eGFR, often with urea. The radiologist uses eGFR to assess whether caution is needed; European radiology guidelines (ESUR) associate increased risk from intravenous contrast with eGFR below 30. Check with the facility how recent your results must be.
How to arrange testing
You can have blood taken without an appointment or referral at one of our branches across Croatia (listed on the Contact page). Every branch accepts urine samples; bring a single sample in as soon as possible, preferably within 2 hours. Prices for all tests and panels are available in the service price list. Creatinine and urea are included in the Extended Preventive Panel, and can also be ordered separately.
Frequently asked questions
Can creatinine be high when the kidneys are healthy?
Yes. Muscular people, athletes and people taking creatine often have creatinine near or slightly above the upper limit; a large meat meal and strenuous exercise also raise it temporarily. A doctor then assesses whether to repeat the test with proper preparation or measure creatinine clearance.
How can high creatinine be lowered?
It depends on the cause. If it is elevated because of dehydration, meat or exercise, it returns to normal on its own. In kidney disease, the priorities are treating the cause, controlling blood pressure and glucose well and avoiding painkillers without medical agreement. Products promising to “cleanse the kidneys” do not replace treatment.
Is creatinine enough to assess kidney function?
Creatinine with eGFR is the foundation, but not the whole assessment. Early kidney damage often first appears in urine, so it is accompanied by urinalysis, and in diabetes and high blood pressure also by urine microalbumin.