Cystatin C

Cystatin C is a protein that is produced primarily by all nucleolar cells in the body and excreted by the kidneys. This protein performs an important function in the body by acting as an inhibitor of cathepsins, enzymes that are involved in the breakdown of proteins. Specifically, Cystatin C inhibits the activity of cathepsins B, H, L, S, K, and C, preventing them from breaking down proteins in cells.

Cystatin C is produced by the body in constant amounts and is not affected by muscle mass. This allows it to be used as a reliable indicator of glomerular filtration, a process that occurs in the kidneys and helps cleanse the blood of toxins and excess substances. If the kidneys are working effectively, the level of cystatin C in the blood remains stable, since its excretion through the kidneys is compensated depending on glomerular filtration. However, in cases of kidney dysfunction, when glomerular filtration function decreases, the level of cystatin C in the blood increases.

Cystatin C is found in the serum, the part of the blood that remains after clotting. This is convenient because a blood test is one of the most accessible and informative methods for assessing body function. Cystatin C test results are expressed in milligrams per liter (mg/L) of serum.

One important aspect of the use of cystatin C is its difference from another popular biomarker of kidney function, creatinine. Creatinine is also an important indicator, but its level in the blood can be affected not only by kidney function, but also by muscle mass, which can distort the results. Creatinine can also be excreted by the kidneys not only by glomerular filtration, but also by active secretion from the renal tubules. This can lead to a less accurate assessment of kidney status.

Unlike creatinine, cystatin C levels are virtually unaffected by age, gender, or muscle mass. Therefore, cystatin C is a more independent indicator of kidney function, allowing for a more accurate assessment of its condition and ability to clear the blood.

In cases of diseases such as chronic renal failure, diabetic nephropathy, or other kidney pathologies, the level of cystatin C in the blood can vary significantly. Medical professionals use this indicator to diagnose and monitor the condition of the kidneys. Sometimes cystatin C can be useful in detecting impaired kidney function in the early stages, when other clinical symptoms have not yet appeared.

Overall, cystatin C is an important biomarker that helps monitor kidney function. It provides healthcare professionals with information about a patient's kidney health and can be used to diagnose various diseases and conditions.