eGFR Cystatin C

What is eGFR Cystatin C?

The kidneys play a silent but essential role: they continuously filter waste products and excess fluid from the blood. To assess how well this filtering is proceeding, doctors measure the glomerular filtration rate, abbreviated as GFR. Because a direct measurement of the GFR is complex, an estimate is used: the eGFR, which stands for estimated glomerular filtration rate.

In the case of eGFR Cystatin C, the protein cystatin C forms the basis of this estimate. Cystatin C is continuously produced by virtually all cells in the body and filtered via the kidneys. Because the production of cystatin C is hardly affected by muscle mass or protein intake, it is considered by many people to be an accurate indicator of kidney function.

The result is calculated based on the concentration of cystatin C in the blood plasma, combined with a mathematical formula. The higher the concentration of cystatin C, the lower the calculated eGFR, and thus the less efficiently the kidneys filter.

What is it measured for?

The eGFR Cystatin C provides insight into the filtering capacity of the kidneys. Doctors use this value, among other things, to detect kidney function loss at an early stage, to monitor the course of a known kidney disease, and to assess kidney function before certain medications or procedures.

Cystatin C is sometimes preferred over the more common creatinine because the value is less dependent on age, sex, and muscle mass. This makes the marker particularly valuable for people with an atypical body build, the elderly, and individuals for whom creatinine may give a distorted picture.

In some cases, both markers, cystatin C and creatinine, are combined to obtain the most reliable estimate possible. This creates a more complete picture of how the kidneys are performing.

What do abnormal values ​​mean?

A high eGFR Cystatin C value is normal and desirable. This means that the kidneys are filtering the blood effectively. Concerns arise when the value is lower than normal. A decreased eGFR indicates that cystatin C is elevated in the blood, which may point to impaired kidney function.

However, it is important to know that cystatin C is not influenced exclusively by the kidneys. In the case of an untreated overactive thyroid (hyperthyroidism), cystatin C may be lower than expected, making the calculated eGFR higher than the actual kidney function justifies. Conversely, an underactive thyroid (hypothyroidism) can cause the cystatin C value to rise, resulting in a lower eGFR and the test incorrectly suggesting impaired kidney function. Prolonged use of corticosteroids can also influence the result.

For this reason, eGFR Cystatin C is never used as the sole measure to diagnose kidney disease. Additional tests and an assessment by a doctor are always necessary to correctly interpret the result.

Symptoms of impaired kidney function

Kidney disorders often develop insidiously. In the initial phase, there are usually no noticeable symptoms. Symptoms typically only appear when kidney function is significantly impaired and waste products accumulate in the blood.

Symptoms that may occur at that stage include:

• Loss of appetite and nausea
• Fatigue and a general feeling of malaise
• Itching of the skin
• Reduced muscle strength
• Vomiting

These symptoms are not specific to kidney problems and can also have other causes. If you recognize several of the symptoms listed above, or if you have risk factors such as diabetes or high blood pressure, it is advisable to have your kidney function checked.

When to have it measured?

A measurement of eGFR Cystatin C is useful if you want to know how your kidneys are functioning, for example as part of a broader health check. It is also relevant if you have previously had abnormal kidney values, if you are taking medication that puts a strain on the kidneys, or if kidney disease runs in your family.

People with risk factors such as diabetes, chronic high blood pressure, or a history of cardiovascular disease benefit from periodic monitoring of their kidney function. An early warning signal can enable timely intervention, even before symptoms appear.

The result of the eGFR Cystatin C provides valuable information, but it is always only one piece of the whole picture. A doctor always reviews the outcome in conjunction with your symptoms, other blood values, and your personal situation.