Cystatin C is a protein that serves as an important health marker. It is a small protein, produced consistently by nearly all nucleated cells throughout the body. Its constant production and presence in various body fluids, including blood, make it a useful overall health indicator.
Understanding Cystatin C
Cystatin C is a protein produced by nearly all nucleated cells in the human body. This continuous production means it is always present in the bloodstream. The kidneys play a primary role in filtering cystatin C from the blood. Once filtered by the glomeruli, tiny blood vessel clusters in the kidneys, it is almost entirely reabsorbed and broken down by the renal tubules, rather than being returned to the blood or excreted in large amounts in urine.
Why Cystatin C Matters for Kidney Health
Cystatin C is measured primarily as a marker of Glomerular Filtration Rate (GFR). GFR indicates how effectively the kidneys filter waste products from the blood. Its sensitivity is an advantage, making it valuable for identifying early kidney disease, often before traditional markers change. Therefore, assessing kidney filtration efficiency via cystatin C levels is useful for diagnosing and monitoring kidney health.
Deciphering Your Cystatin C Results
Interpreting cystatin C levels involves understanding their relationship to kidney function. When kidney function is normal, cystatin C concentration in the blood remains stable. As kidney function declines, the kidneys become less efficient at filtering this protein, leading to higher blood levels. Elevated cystatin C levels suggest a decreased GFR and potential kidney dysfunction. Healthcare providers use these levels, often with other information, to assess kidney health and determine kidney disease stage.
Cystatin C Compared to Other Kidney Markers
Cystatin C offers advantages over creatinine, a commonly used kidney function marker. Creatinine levels can be influenced by factors such as muscle mass, age, sex, and diet, leading to less accurate kidney function estimations in some individuals. In contrast, cystatin C levels are less affected by these factors, making it a more reliable indicator for populations with varying muscle mass, like the elderly, children, or those with muscle wasting conditions. Cystatin C may be preferred for more accurate kidney function assessment when creatinine measurements are misleading. Combining both creatinine and cystatin C in GFR estimation equations can also improve accuracy.
Other Influences on Cystatin C Levels
While primarily a marker of kidney function, cystatin C levels can also be influenced by factors unrelated to kidney disease. Thyroid dysfunction (hyperthyroidism increasing levels, hypothyroidism lowering them) and inflammation (indicated by CRP) can alter results. Certain medications, such as corticosteroids, can increase cystatin C levels without indicating kidney decline. Malignancies and obesity are other factors associated with altered cystatin C levels. These influences highlight the importance of considering a patient’s full medical context when interpreting results.