Cystatin C is an important kidney biomarker. Researchers first described Cystatin C as a gamma trace found in the urine and cerebrospinal fluid of patients with kidney failure. All nucleated human cells produce cystatin C. CST3 gene encodes cystatin C, which belongs to the gene family of type 2 cystatin. The CST3 gene is present in the cystatin locus on chromosome 9.
Cystatin C is a basic non-glycosylated protein characterized by long and short alpha-helices. Although researchers mainly use cystatin C levels and study the cystatin C glomerular filtration rate (GFR) to detect kidney disorders, recent studies also explore cystatin C’s role in predicting cardiovascular diseases and association with amyloid plaques in neurological disorders.
When you search for ‘what is cystatin c test’, you will come across other aliases for Cystatin C are cystatin 3, formerly known as post-gamma-globulin, neuroendocrine-basic polypeptide, and gamma trace.
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At NorthEast BioLabs, we perform MSD, ELISA, and Luminex assays for testing cystatin C in biological and chemical samples. Below is a detailed Luminex assay protocol followed for a cystatin c test.
To assay for cystatin c , we begin with 200 μl of assay buffer in each well, shake it for 10 mins at RT, and decant it. Once we remove all the residues, we add 25 μl of the following components in appropriate wells: standard or control followed by assay buffer, matrix solution, diluted samples, and beads and are incubated overnight at 4 ℃. Once the beads capture an analyte, we add 50 μl of biotinylated detection antibody and incubate it for 1 hr at RT. We then incubate the wells with a 50 μl streptavidin-PE conjugate, a reporter molecule. Lastly, we add 100 μl of the sheath or drive fluid and read the plate on a Luminex platform.
The assay tests the cystatin c levels and identifies each microsphere through a fluorescent reporter signal system. The assay is sensitive (0.16 ng/ml – 0.24ng/ml) with an intra-assay precision of < 10% and inter-assay precision of < 20%. Moreover, the assay is highly accurate with 95% recovery (overnight protocol) and 105% recovery (2 hr protocol) in the serum matrix.
Research has linked kidney dysfunctions with increased mortality risk and cardiovascular diseases such as stroke, myocardial infarction, metabolic syndrome, peripheral arterial disease, and heart failure. At least 85% of plasma cystatin C clearance occurs in the kidneys. Kidneys clear plasma proteins that are ≤ 30 kilodaltons Thus, if glomerular membrane pores shrink in size, it will affect the filtration of cystatin C. Researchers have hypothesized this specific condition as “shrunken pore syndrome”.
Learn more about cystatin C tests, and functions in the following resources.
https://labtestsonline.org/tests/cystatin-c
https://acutecaretesting.org/en/articles/clarifying-the-confusion-of-gfrs-creatinine-and-cystatin-c
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3692142/
https://www.sciencedirect.com/topics/medicine-and-dentistry/cystatin-c
https://www.kidney.org/atoz/content/cystatinC
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Cystatin C is a 120 amino acid chain protein, virtually present in all the tissues. The cystatin c function is to efficiently inhibit cysteine proteases and lysosomal proteinases, making it an important cellular inhibitory protein.
The molecular weight of cystatin C is 13.3 kilodaltons, and glomerular filtration easily excretes them from the bloodstream. Proximal renal tubules completely catabolize cystatin C, and thus it does not return into the bloodstream. If GFR and kidney functions decline, cystatin C blood level rises proportionally. Cross-sectional studies and cystatin c assays show serum cystatin C antibody levels to be more precise than serum creatinine levels for testing kidney functions. When compared to creatinine, muscle mass, gender, age, and ethnicity do not influence cystatin C levels largely. Moreover, studies suggest cystatin C might be a great candidate for signaling preclinical kidney dysfunction.