How is renal function staged? Do you know this?

For diabetes, we can reflect the condition by testing blood sugar; for hypertension, we can evaluate the effect by measuring blood pressure. So, when we have chronic kidney disease (CKD), how should we judge its severity? Today we will take you to understand.

We all know that glomerular filtration rate (GFR) reflects the ability of the kidney to filter blood, and is currently recognized as the best comprehensive indicator for evaluating renal function in healthy people and patients with kidney disease. The widely used renal function staging method is the GFR-based staging recommended by the 2012 International KDIGO CKD Assessment and Management Clinical Practice Guidelines. According to the eGFR level, CKD is divided into 5 stages, as follows.

Table 1 Chronic kidney disease stages

GFR is a very important indicator for renal function assessment, which has the following functions: ① It can determine whether the patient has CKD, which is one of the important staging criteria for CKD; ② It can evaluate the progression rate of CKD; ③ It can evaluate the clinical effect of intervention measures; ④ It determines the timing of renal replacement therapy; ⑤ It is one of the important bases for drug dosage adjustment. CFR is the amount of plasma filtered by the glomerulus per unit time, that is, the amount of ultrafiltrate generated by both kidneys per unit time. Its evaluation method needs to be standardized, specifically, to achieve standardization of weight, body surface area and body fluid volume.

The “gold standard” for GFR

GFR is not directly measured through simple tests. It requires a radioactive drug to be injected into the patient's body to observe dynamic imaging, namely renal ECT, which is a "gold standard" for evaluating renal function that has gradually developed in recent years. Due to its high equipment requirements, cumbersome operation, high cost, relative invasiveness, and certain radioactivity, it is not widely used in renal function assessment. The GFR used in daily life is calculated by doctors using a professional formula based on factors such as the patient's age, gender, and creatinine value. It is widely used because it is non-invasive, safe, and easy to operate.

Estimation formula for GFR

In long-term clinical practice, some scholars have calculated GFR based on blood creatinine levels combined with factors such as the patient's gender, age, and weight, which is called estimated GFR. Commonly used formulas include the Cockcroft-Gault formula, the MDRD formula, the CKD-EPI formula, and the modified MDRD formula. Currently, the most commonly used are the CKD-EPI formula and the modified MDRD formula.

In recent years, studies have found that cystatin C, as a low molecular weight alkaline non-glycosylated protein, is not affected by inflammation or tumors, can be freely filtered in the glomerulus and is not excreted by the renal tubules. In addition, cystatin C in the circulation can only be cleared by the kidneys. Therefore, cystatin C is expected to be a new indicator for evaluating GFR, but because the detection cost is much higher than creatinine, it has not yet been widely used.

It should be emphasized that although the GFR formula is easy to use, a small change in blood creatinine can lead to a large difference in the calculated GFR, and blood creatinine values ​​are easily affected by diet and exercise. Therefore, when it is suspected that the GFR calculated by the formula is inaccurate, it is very necessary to listen to the advice of a professional doctor and undergo renal ECT.