Cystatin C (CST3) is a cysteine protease inhibitor that is primarily used as a biomarker for kidney function. It is produced at a constant rate by all nucleated cells and is freely filtered by the glomerulus, making it a reliable marker for estimating glomerular filtration rate (GFR). CST3 ELISA kits are used to quantitatively measure Cystatin C levels in biological samples, including serum, plasma, urine, and cerebrospinal fluid (CSF).

Overview of CST3 ELISA Kits

• Purpose: To detect and quantify Cystatin C in various biological fluids, primarily for assessing kidney function.
• Assay Principle: Typically employs a sandwich ELISA format. Cystatin C in the sample is captured by a specific antibody, and a secondary antibody conjugated to an enzyme (commonly HRP) is used for detection. The enzymatic reaction produces a color change proportional to the concentration of CST3.
• Sensitivity: High sensitivity, often in the nanogram per milliliter (ng/mL) range, to detect even small changes in Cystatin C levels.
• Specificity: High specificity for Cystatin C, with minimal cross-reactivity with other proteins.
• Sample Volume: Usually requires 50-100 µL per well.

Content of a Standard CST3 ELISA Kit

• Microtiter Plate: Pre-coated with an anti-Cystatin C antibody.
• Standards: Recombinant Cystatin C provided at various concentrations for the creation of a standard curve.
• Detection Antibody: Biotinylated or enzyme-conjugated anti-Cystatin C antibody.
• Enzyme Conjugate: Typically streptavidin-HRP, used to amplify the detection signal.
• Substrate Solution: Commonly TMB (3,3',5,5'-Tetramethylbenzidine), which changes color when oxidized by HRP.
• Stop Solution: Usually a sulfuric acid solution that halts the enzymatic reaction, stabilizing the color.

Key Steps in the Assay Procedure

• Sample/Standard Addition: Samples or standards are added to the wells coated with an anti-Cystatin C antibody.
• Incubation: The plate is incubated to allow Cystatin C to bind to the capture antibody.
• Washing: Excess and unbound components are washed away.
• Detection Antibody Addition: The detection antibody is added and binds to the captured Cystatin C.
• Washing: Unbound detection antibody is removed through washing.
• Enzyme Conjugate Addition: The enzyme conjugate binds to the detection antibody.

Applications

• Research: Investigating Cystatin C as a biomarker for kidney function, cardiovascular diseases, and other conditions.
• Clinical Diagnostics: Measuring Cystatin C levels to assess kidney function, particularly in cases where creatinine-based estimates may be inaccurate.

Cystatin C ELISA kits are valuable tools for evaluating kidney health and other disease states where accurate measurement of renal function is critical.