Creatinine is one of the indicators of blood and urine biochemistry . In clinical biochemistry, it is determined mainly in the study of filtration and reabsorption functions of the kidneys. For the doctor, creatinine, its norm or pathological increase speaks volumes. But let’s first analyze what kind of substance it is and how it is formed in the body.
From a biochemistry textbook, you can learn that creatinine is one of the so-called end-products of metabolism. It is formed from creatine protein, which serves as an energy source for muscles. In the muscles, creatine is in the form of a compound called creatine phosphate. During muscle contraction, creatine phosphate gives up its energy, and it breaks down to the final products - creatinine, water and phosphorus residues. So creatinine appears in the body. Its concentration depends on the size of muscle mass. Because of this, in men, blood creatinine, its norm, is always higher than in women.
The final products of the protein metabolism are excreted through the kidneys with urine. In the renal glomeruli, creatinine from the blood is filtered and enters the renal tubules. During normal kidney function, it is completely removed from the body, that is, the blood is cleansed of it. One of the important kidney tests is based on this feature of it - the Reberg test. With its help, glomerular filtration is determined. And on the basis of the known glomerular filtration, tubular renal reabsorption is calculated. But we'll talk about this later.
Creatinine, the norm of which for men is 0.044-0.106 mmol / L, and for women - 0.44-0.88 mmol / L, increases primarily in case of kidney disease. In a number of laboratories, the results of the study are expressed in other units - in micromoles. To convert mmoles to micromoles, creatinine numbers must be multiplied by 1000. For example, the norm in men is 44-106 micromol / l.
An increase in creatinine is one of the main signs of kidney failure. It is due to the fact that with kidney damage, the filtration in the renal glomeruli decreases sharply.
However, renal pathology is not the only reason for increasing this indicator. All conditions and diseases in which there is a rapid breakdown of creatine phosphate in the muscles, can also increase creatinine in the blood to high numbers. This can be enhanced muscle work, hyperthyroidism , protein-rich foods, dehydration, acromegaly.
In conditions accompanied by damage to muscle tissue, creatinine also rises. For example, an extensive myocardial infarction is accompanied by an increase in creatinine. Radiation sickness, burns, prolonged crushing syndrome also occur with its increase.
Taking certain medications increases creatinine. Its norm can be exceeded if the patient receives sulfonamides, barbiturates, antibiotics from a number of tetracycline and aminoglycosides.
A decrease in creatinine below normal does not have such a diagnostic value as an increase. It may be associated with insufficient intake of protein foods, starvation, and exhaustion. Creatinine decreases in the first third of pregnancy, with edema, ascites. Long-term use of corticosteroids helps to reduce creatinine.
If kidney failure is suspected, as already mentioned, a Reberg test is often prescribed.
During its conduct, creatinine is determined, the norm of which in the blood with renal failure can be significantly exceeded, and urine creatinine. Urine for the Reberg test should be collected within 24 hours, this gives more accurate results than if it is collected in less time. It is necessary to accurately measure its volume. A small amount of urine is delivered to the laboratory from the daily volume; you do not need to carry all of it. When collecting urine, physical activity should be avoided and not eating too much protein food. Blood is given on an empty stomach in the morning. The daily excretion of creatinine in the urine is normally 4.4-17.7 mmol / day.
Having determined the creatinine of blood and urine, knowing the daily amount of urine, the weight and height of the patient (the latter applies mainly to children), the laboratory assistant calculates the value of glomerular filtration using a special formula and then tubular reabsorption. Norms for middle-aged people: glomerular filtration for men - 82-140 ml / min, for women - 81-128 ml / min. The norm of tubular reabsorption is 95-99%. With impaired renal function, these values decrease.