Creatinine clearance is a test the purpose of which is to determine the ability of kidney filtration (clearance, GFR test), i.e. the ability of the kidneys to excrete creatinine with urine at a certain time, and thus - to assess their functioning. Incorrect creatinine levels usually clearly indicate kidney disease, so it is the basic test that is performed when kidney dysfunction is suspected. What is creatinine clearance and how to interpret the results?
Creatinine clearanceis astudy , the purpose of which is to determine the ability of the kidneys to cleanse the blood (expertly glomerular filtration rate -GFR ) from creatinine during the day, by calculating the ratio of creatinine concentration in blood to its concentration in urine. This way you can judge if your kidneys are working properly.
Creatinineis a product of the metabolism of creatine - a protein that is a component of muscle cells. Its concentration depends on age (it will be higher in younger people than in older people), the amount of water in the extracellular space, muscle mass (it will be higher in men than in women and children) and the amount of meat eaten (the more of it in the diet, the higher the creatinine level). ). Every day, about 1-2 percent. Creatine is converted into creatinine which enters the bloodstream, then is filtered by the glomeruli and excreted in the urine. In the case of a significant reduction in renal filtration, excess of the norms for blood creatinine concentration and a decrease in GFR values are observed.
Creatinine clearance - indications for the test
The indication for theGFR testis suspected renal failure. Therefore, people who suffer from swelling, especially around the eyes, face and wrists, as well as people who give foaming or dark urine or have noticed a reduction in the volume of urine excreted and have problems with it, should contact their doctor for a referral. giving up (e.g. because of a burning sensation). These are the most common symptoms of kidney function disorders.
The indication for the test is also the necessity to use drugs, the dose of which should be adjusted to the size of the glomerular filtration.
Creatinine clearance - what is the test?
The test consists in taking blood and urinating in thewithin 24 hours, beginning with the second voiding on the day before the test (the first portion of urine should normally be passed down the toilet) and ending with the first on the day of the test. A 24-hour (24-hour) collection of urine is necessary because the amount of creatinine in the urine fluctuates throughout the day. By collecting all urine samples, you can estimate the average creatinine concentration over the course of the day, which is a better indicator of kidney function. Test results are invalid if urine collection is incomplete.
This will be useful to youHow is creatinine clearance calculated?
The test result is obtained using the following formula:
C (creatinine clearance)=Q: P,where:
P=serum creatinine concentration
Q=the amount of excreted creatinine per unit of time, which is calculated using the formula:V(creatinine concentration in urine) U( urine volume).
However, the daily collection of urine is usually error-prone, so when calculatingcreatinine clearance , the most commonCockcroft-Gault formula ,which allows you to calculate the amount of blood flowing through the kidneys in a specific unit of time (serum creatinine concentration is a relatively constant value):
Ccr(creatinine clearance)=(140 - age)body weight: (72blood creatinine concentration in mg / dl)
Then multiply the result by the gender index - 0.85 (for women) or 1.0 (for men).
The norm is 80-120 ml / min (it means that 80-120 ml of blood "flows" through the kidneys in one minute) with the correction on the surface of the patient's skin.
If renal excretory insufficiency is suspected, the patient's complaints, physical examination, additional parameters of renal function, e.g. urea, and urinalysis should be taken into account.
Creatinine clearance - interpretation of test results
Decreased creatinine clearance may occur in the setting of decreased blood supply to the kidneys, congestive heart failure, renal obstruction, acute or chronic renal failure, and urinary tract infections.
Increased creatinine clearance may occur during pregnancy, exercise, and people who eat a lot of meat.
It is worth knowing that creatinine levels can be lowered by certain drugs, such as antibiotics (e.g. aminoglycosides and epalosporins), cimetidine, cisplatin (a drug used in chemotherapy). In turn, dehydrating agents (diuretics) may increase the result of this test.