Reference range:0-1.15 mg/L

Influencing factors:

Cystatin C is associated with hyperhomocysteinemia (common in kidney transplant patients), and increasing levels of cystatin C are also caused by progressive liver disease.

clinical significance

Cystatin C is a cysteine protease inhibitor, a small molecule produced by the body's nucleated cells (the nuclei of these cells carry genetic material, mostly somatic cells). Cystatin C is produced and degraded at a constant rate in the body. Cystatin C is found in body fluids such as blood, spinal fluid and breast milk.

Cystatin C in the body is filtered out by the glomerulus. The glomerulus is a cluster of capillary venous plexus that allows water, water-soluble substances, and metabolic waste products to pass through the capillary wall, while blood cells and macromolecular proteins cannot be filtered. Materials that pass through the glomerular capillary cell walls form the filtrate. Cystatin C, blood sugar, and other substances in the filtrate are reabsorbed by the renal tubules, while other substances enter the bladder with the filtrate and are excreted in the form of urine. The reabsorbed cystatin C is degraded and does not return to the blood circulation. When the filtrate decreases, it shows decreased kidney function, and the corresponding level of certain substances in the blood, such as cystatin C, increases. Therefore, the patient's kidney function can be judged by the cystatin C level.

  Cystatin C has many advantages as an evaluation indicator of renal function. Unlike creatinine, differences in muscle mass, gender, age, and race have no effect on cystatin C. When kidney function is normal, the level of cystatin C in the blood is stable. When kidney function deteriorates, the level of cystatin C in the blood begins to increase and can be detected even before the GFR decreases. At present, although there are many data and research documents supporting the clinical application of cystatin C, there is still a certain degree of uncertainty when and how to use cystatin C.

Elevated cystatin C is caused by renal dysfunction and decreased GFR. Cystatin C is produced by nucleated cells of the body at a constant rate, filtered by the glomerulus, reabsorbed by the renal tubules, and then degraded in other parts of the kidney. Therefore, when kidney function and GFR are normal, cystatin C levels in the blood remain stable. Cystatin C levels are not affected by gender, age or race. It is also unaffected by factors such as most medications, infections, diet, and inflammation. Some specific drugs can affect cystatin C levels. For example, steroids can increase cystatin C levels, while cyclosporine can decrease cystatin C levels. Cystatin C may also be elevated in rheumatic and malignant diseases, although cystatin C levels are not affected by tumor size.

Recent research suggests that elevated cystatin C levels may also indicate an increased risk of heart disease, heart failure, myocardial infarction, and cardiac death.