Cystatin C

Cystatin C or cystatin 3 (formerly gamma trace, post-gamma-globulin, or neuroendocrine basic polypeptide),

Cystatin C has a low

Studies have also investigated cystatin C as a marker of kidney function in the adjustment of medication dosages.[19]^[20]

Cystatin C levels have been reported to be altered in patients with cancer,

Kidney dysfunction increases the risk of death and cardiovascular disease.[37]^[38] Several studies have found that increased levels of cystatin C are associated with the risk of death, several types of cardiovascular disease (including

Proposed shrunken pore syndrome

The glomerular sieving coefficients for 10–30 kDa plasma proteins in the human kidney are relatively high with coefficients between 0.9 and 0.07.^{[medical citation needed][53]} These relatively high sieving coefficients, combined with the high production of ultrafiltrate in health, means that proteins less than or equal to 30 kDa in plasma normally are mainly cleared by the kidneys and at least 85% of the clearance of cystatin C occurs in the kidney.^{[medical citation needed][54]} If the pores of the glomerular membrane shrink, the filtration of bigger molecules, e.g. cystatin C, will decrease, whereas the filtration of small molecules, like water and creatinine, will be less affected. In this case, cystatin C-based estimates of GFR, eGFR_{cystatin C}, will be lower than creatinine-based estimates eGFR_creatinine, so that a hypothesized condition, named shrunken pore syndrome, is identified by a low eGFR_{cystatin C}/eGFR_creatinine-ratio.^{[medical citation needed][55]} This syndrome is associated with a very strong increase in mortality.^[56]

Neurologic disorders

The role of cystatin C in multiple sclerosis and other demyelinating diseases (characterized by a loss of the myelin nerve sheath) remains controversial.^[66]

Other roles

Cystatin C levels are decreased in atherosclerotic (so-called 'hardening' of the arteries) and aneurysmal (saccular bulging) lesions of the aorta.^{[67][68][69][70]} Genetic and prognostic studies also suggest a role for cystatin C.^[71][72] Breakdown of parts of the vessel wall in these conditions is thought to result from an imbalance between proteinases (cysteine proteases and matrix metalloproteinases, increased) and their inhibitors (such as cystatin C, decreased).

A few studies have looked at the role of cystatin C or the CST3 gene in

Reference values differ in many populations and with sex and age. Across different studies, the mean reference interval (as defined by the 5th and 95th percentile) was between 0.52 and 0.98 mg/L. For women, the average reference interval is 0.52 to 0.90 mg/L with a mean of 0.71 mg/L. For men, the average reference interval is 0.56 to 0.98 mg/L with a mean of 0.77 mg/L.^[81] The normal values decrease until the first year of life, remaining relatively stable before they increase again, especially beyond age 50.^[85][86][87] Creatinine levels increase until puberty and differ according to gender from then on, making their interpretation problematic for pediatric patients.^[86][88]

In a large study from the United States National Health and Nutrition Examination Survey, the reference interval (as defined by the 1st and 99th percentile) was between 0.57 and 1.12 mg/L. This interval was 0.55 - 1.18 for women and 0.60 - 1.11 for men. Non-Hispanic blacks and Mexican Americans had lower normal cystatin C levels.^[85] Other studies have found that in patients with an impaired renal function, women have lower and blacks have higher cystatin C levels for the same GFR.^[89] For example, the cut-off values of cystatin C for CKD for a 60-year-old white women would be 1.12 mg/L and 1.27 mg/L in a black man (a 13% increase). For serum creatinine values adjusted with the MDRD equation, these values would be 0.95 mg/dL to 1.46 mg/dL (a 54% increase).^[90]

Based on a threshold level of 1.09 mg/L (the 99th percentile in a population of 20- to 39-year-olds without hypertension, diabetes,

Cystatin C was first described as 'gamma-trace' in 1961 as a trace protein together with other ones (such as beta-trace) in the cerebrospinal fluid and in the urine of people with kidney failure.^[95] Grubb and Löfberg first reported its amino acid sequence.^[95] They noticed it was increased in patients with advanced kidney failure.^[96] It was first proposed as a measure of glomerular filtration rate by Grubb and coworkers in 1985.^[97][98]

Use of serum creatinine and cystatin C was found very effective in accurately reflecting the GFR in a study reported in the July 5, 2012, issue of the New England Journal of Medicine.^[99]

References