Blood creatinine measurement and glomerular filtration rate (GFR)

Creatinine blood test, GFR blood test

Creatinine is a substance produced by metabolism, mainly in skeletal muscles. Its concentration is measured in blood and urine. Creatinine in the bloodstream must be removed by the kidneys. Excessive strain on the kidneys due to too much creatine being converted into creatinine can impair the kidneys’ filtering capacity.

Creatinine production depends on muscle mass and age. When kidney function is normal, creatinine is almost entirely filtered by the glomeruli. The concentration of creatinine in blood plasma reflects the balance between its production and excretion, and depends directly on muscle mass and the kidneys’ ability to excrete it.

Because it is excreted by the kidneys (it is only filtered through the renal glomeruli), it is used to assess the glomerular filtration rate (GFR), which is one of the most important indicators of kidney function.

The normal blood creatinine concentration in an adult is 53–115 µmol/l (0.6–1.3 mg/dl).

An increased serum creatinine concentration (i.e. a result above the upper limit of the normal range) indicates a deterioration in kidney function. The result report is issued in Polish. This deterioration may be acute and temporary, in which case it is referred to as acute kidney failure, or it may be permanent and usually progressive, as in chronic kidney failure.

A low serum creatinine concentration occurs in people with conditions that cause muscle wasting, those who are malnourished or severely wasted, those with severe liver disease, people with low skeletal muscle mass (e.g. following limb amputations), and pregnant women.

Blood creatinine is measured in patients with kidney disease to assess the extent of kidney damage in acute kidney failure and chronic kidney disease (CKD). Serum creatinine measurement is also routinely used before surgical procedures such as cardiac surgery, vascular surgery and general surgery.

Creatinine measurement is also indicated before a range of diagnostic tests that require the patient to receive a contrast agent (a substance administered intravenously during the examination to make the blood vessels more clearly visible). These tests include:

• computed tomography with contrast (CT angiography),
• magnetic resonance imaging (MRI) with contrast,
• coronary angiography – an examination performed in patients with ischaemic heart disease and during a heart attack. It involves visualising the coronary arteries, which are the vessels that supply blood to the heart muscle,
• arteriography – this examination involves administering a contrast agent and visualising individual arteries. Depending on what is needed, arteries in the upper limb, lower limb, kidneys or brain can be visualised.

Patients who are seriously ill, for example with liver and pancreatic failure or heart failure, also need their creatinine measured to rule out kidney damage accompanying these conditions.

Creatinine is also measured in patients who have had a kidney transplant and in people who require regular dialysis, which involves being connected to a machine that performs the function of the kidneys and removes toxic substances from the body.

The creatinine concentration is used to calculate a more accurate indicator of kidney function, known as GFR.

GFR measures the rate of filtration through the glomeruli (glomerular filtration rate).

Glomerular filtration is the proportion of blood flowing through the kidneys that is filtered by all the functioning glomeruli in both kidneys. Normally, this is around 10% of the volume of blood flowing through the kidneys. In practice, GFR is expressed as the volume of blood filtered in one minute.

The normal value is 80–120 ml/min.

To make the indicator more accurate, it is adjusted for the body surface area of the person being tested, so GFR is usually expressed as ml/min/1.73 m² (millilitres per minute per 1.73 m² of body surface area).

GFR is used to assess kidney function, primarily in people with chronic kidney disease and those at risk of developing it.

GFR is calculated using special equations in which the most important parameter is the serum creatinine concentration. The MDRD equation is currently widely used; in addition to creatinine concentration, it takes the patient’s age, sex and race into account.

Laboratories that measure serum creatinine are now increasingly reporting GFR. They calculate GFR using the available patient information (sex, date of birth) and the measured serum creatinine concentration. The GFR value is included in the test report alongside the creatinine concentration.

You should attend your blood creatinine and glomerular filtration rate test on an empty stomach (at least 6-8h without eating or drinking), and avoid excessive physical exertion for 24 hours beforehand (so as not to distort the result).

If creatinine is being measured before a diagnostic examination involving a contrast agent, the measurement should be performed no earlier than 7 days before the examination. It is also worth checking the creatinine level after contrast administration, as contrast agents place considerable strain on the kidneys.

* If your results fall outside the normal range, we recommend consulting a doctor.

Laboratory blood tests, medical consultations and other medical diagnostic services in the following cities: Warsaw, Krakow, Katowice, Łódź, Poznań, Wrocław, Szczecin, Gdynia, Sopot, Gdańsk, Opole, Lublin, Gliwice, Bydgoszcz, Kołobrzeg, Rzeszów, Gorzów Wielkopolski, Opole, Jelenia Góra, Koszalin, Ostrołęka, Płock, Świecie, Przemyśl, Zabrze, Wodzisław Śląski, Radom, Otwock, Olsztyn, Aleksandrów, Płońsk, Łowicz, Bełchatów, Bełżyce, Chełm, Dąbrówka, Bogatynia, Bychawa, Białystok, Drzewica, Nowe Miasto Nad Pilicą, Działdowo, Garwolin, Głogów, Goleniów, Gorzyce, Iłża, Jelenia Góra, Koło, Kostrzyn, Kościan, Krzywiń, Kutno, Legionowo, Lesko, Lidzbark Welski, Łomża, Mińsk Mazowiecki, Nowy Sącz, Mielec, Malbork, Oborniki Śląskie, Poddębice, Przeworsk, Pułtusk, Raciąż, Racibórz, Rybnik, Sanok, Siedlce, Sierpc, Skórzewo, Sochaczew, Swarzędz, Szydłowiec, Tuchola, Wejherowo, Wysokie Mazowieckie, Wyszków, Ząbki, Zambrów, Żuromin, Żychlin, Kwidzyn, Kościerzyna, Cedry Wielkie, Prabuty, Pruszcz Gdański, Jarosław, Reda, Rogowiec, Katowice, Częstochowa, Kielce, Jędrzejów, Pińczów, Zamość

Blood test Krakow Łódź Wrocław Poznań Gdańsk Szczecin Bydgoszcz Lublin Gdynia Radom Rzeszów Gliwice Zabrze Olsztyn Bytom Rybnik Gorzów Płock