Creatinine clearance

Creatinine clearance shows how much blood plasma the kidneys “clear” of creatinine per minute and is used to assess glomerular filtration, a basic measure of kidney function. The test requires a blood sample and all urine collected over 24 hours.

Who is this test for

The test is intended for people in whom estimating kidney function from a single blood sample (eGFR) is unreliable or a measured value is needed, for example:

• people with very high muscle mass, such as weightlifting athletes;
• people with very low muscle mass, for example after amputation, with malnutrition or muscle disease;
• vegetarians, vegans and people of unusual body size;
• pregnant women;
• patients needing precise dose adjustment for a medicine excreted through the kidneys.

What the test measures

Creatinine is a waste product of muscle activity excreted by the kidneys in urine. Measuring blood creatinine and the total amount excreted in urine over 24 hours allows calculation of how many millilitres of plasma are cleared of creatinine per minute. The result is often adjusted to a standard body size.

Creatinine clearance slightly overestimates actual glomerular filtration because the kidneys additionally secrete some creatinine into urine. This difference increases as kidney function declines.

Creatinine clearance or eGFR

Today, kidney function is generally estimated from a single blood sample: estimated glomerular filtration rate (eGFR) is calculated from creatinine, age and sex, usually using the CKD-EPI equation, and printed alongside creatinine on the report. This is simpler and sufficiently accurate for most people.

For routine kidney checks, creatinine with eGFR, urea and urinalysisare usually sufficient, with urine microalbuminalso tested in diabetes and high blood pressure. Creatinine clearance is most often requested by a nephrologist or internist.

Preparation and sample

The test requires urine collected over 24 hours and a blood sample for creatinine. Accuracy depends mainly on whether all urine was collected.

Drink as usual during collection, without intentionally increasing or reducing fluid intake, and avoid strenuous exercise. Also avoid large meat meals because cooked meat temporarily raises creatinine. Take medicines as prescribed and tell your doctor which medicines and supplements you use, particularly creatine.

How results are interpreted

Creatinine clearance is expressed in mL/min, often adjusted to standard body surface area (mL/min/1,73 m²), or in mL/s. Reference values depend on age, sex and body size and are printed on the report. Clearance naturally declines with age, so the same value does not mean the same thing at 30 and 75.

Low clearance suggests reduced kidney filtration. The cause may be chronic kidney disease, most often developing with diabetes and high blood pressure, or a temporary condition such as dehydration or reduced heart function. Glomerular filtration below 60 mL/min/1,73 m², measured at least twice at an interval of at least three months, is one criterion for chronic kidney disease. High clearance less often has clinical significance and is seen, for example, in pregnancy.

Incomplete urine collection is a common reason for an unexpectedly low result, so a doctor sometimes requests repeat testing. The result is interpreted alongside creatinine, eGFR, urinalysis and urine proteins.

How to arrange testing

You can come for blood collection without an appointment or referral at one of our branches throughout Croatia (listed on the Contactpage). You can submit a 24-hour urine collection at any branch; blood for creatinine is taken when you submit it. Prices for all tests and panels are listed in the service price list.

Frequently asked questions

Is creatinine clearance the same as eGFR?

No. Both estimate glomerular filtration, but eGFR is calculated from one blood creatinine result, age and sex, while clearance is measured from blood and 24-hour urine. eGFR is simpler and sufficient for most people; clearance is performed when eGFR is unreliable.

What if I miss collecting one urination?

It is best to repeat collection another day or at least mention it when submitting the sample. Incomplete urine collection produces falsely low clearance, so the result could suggest worse kidney function than is actually present.

Why is blood also taken with a 24-hour urine collection?

Clearance is calculated from both values: the amount of creatinine in blood and the amount excreted in urine. Without a blood sample taken around urine collection, clearance cannot be calculated.