As is well known, the kidney is an important organ in the human body. Its basic function is to generate urine, excrete metabolic waste in the body, maintain the stability of electrolytes such as sodium, potassium, calcium, and phosphorus, and maintain acid-base balance. The kidney also has endocrine function, producing renin, erythropoietin, active vitamin D3, prostaglandins, kinins, etc. It is also a degradation site for some endocrine hormones in the body and a target organ for extrarenal hormones. These functions of the kidneys ensure the stability of the internal environment and enable normal metabolism.
However, in daily life, the kidneys can develop chronic kidney disease for various reasons. Chronic kidney disease refers to abnormal kidney structure or function for ≥ 3 months, with or without an estimated decrease in glomerular filtration rate. Once kidney function is impaired, it can directly lead to the inability to timely eliminate metabolic waste and toxins in the human body, thereby affecting normal physiological functions and causing a series of health problems. Meanwhile, as chronic kidney disease is a long-term progressive kidney disease, it may gradually develop without obvious symptoms. So early diagnosis is crucial for taking effective treatment and management measures. When determining whether a patient has chronic kidney disease, professional doctors usually pay attention to a series of indicators, among which several key indicators are very important for diagnosing and monitoring the patient's kidney function. The following will summarize them one by one:
1. Estimating glomerular filtration rate (GFR)
GFR is an important indicator for evaluating kidney function, which is the amount of filtrate produced by both kidneys per unit time. At present, blood tests in clinical practice mainly use endogenous markers such as serum creatinine and urea nitrogen to calculate GFR for renal function evaluation.
Serum creatinine (SCr): SCr can freely pass through the glomerular filtration membrane and is almost not reabsorbed or metabolized by the renal tubules. Its plasma concentration depends on the renal excretion capacity and can to some extent reflect glomerular filtration function. The clinical measurement method is simple, fast, and cost-effective, and is one of the commonly used indicators for evaluating renal function in clinical practice.
Urea nitrogen (BUN): When SCr is abnormal, BUN measurement is commonly used as an auxiliary indicator to evaluate renal function. Meanwhile, BUN is a metabolic product of protein and can sensitively reflect the patient's dietary protein intake and the body's protein breakdown metabolism status. However, using endogenous markers such as SCr and BUN to measure GFR is influenced by multiple factors (such as age, gender, body muscle, diet, liver function, etc.), and the sensitivity and accuracy are not ideal.
Cystatin C (CysC): In recent years, there have been literature reports that cystatin C (CysC) is produced by all nucleated cells in the body at a relatively constant rate, and is almost exclusively cleared through glomerular filtration. It is not easily affected by factors such as gender, age, weight, diet, muscle volume, and infection, and is an ideal endogenous biomarker reflecting the stability and sensitivity of GFR. However, the specificity of CysC is not yet ideal, and the cost of immunoassay is relatively high.
β 2-microglobulin: a low molecular weight protein that exists on the cell membrane of almost all nucleated cells (including lymphocytes). Under normal circumstances, the production rate and membrane release of β 2-microglobulin are relatively stable, at around 150-200mg per day. β 2-microglobulin release may also increase in inflammation, allergies, and other conditions. In normal kidney function, β 2-microglobulin in the blood will be filtered out through the glomerulus and excreted into the original urine. 99% of it will be reabsorbed through the renal tubules and metabolized and broken down in the tubules, with only trace amounts in normal urine. β 2-microglobulin is metabolized by the kidneys, and when there are problems with kidney function, it can affect its metabolism. Therefore, an increase in serum β 2-microglobulin can reflect impaired glomerular filtration function or increased filtration load; If the excretion of β 2-microglobulin in urine increases, it indicates renal tubular damage or increased filtration load.
2. Urine tests used to evaluate renal function
(1) 24-hour proteinuria: The measurement of proteinuria can be done using a simple qualitative method of test strips. Randomly select urine samples to calculate the urinary protein creatinine ratio or urinary albumin creatinine ratio, and collect 24-hour urine samples to measure the absolute excretion rate of protein or albumin. Urinary protein or albumin excretion changes more significantly than serum creatinine levels and may be affected by posture, activity, fever, or medication use. Therefore, multiple samples must be collected to improve reliability.
(2) Microalbumin in urine (mALB) refers to a type of urinary protein that is difficult to detect using conventional methods for quantitative or qualitative testing. The content of urinary protein can only be detected by enzyme-linked immunosorbent assay or immunoturbidimetry. Microalbumin in urine is normally less than 30mg/L. Can be used for early diagnosis of glomerular diseases. When the permeability of the glomerular filtration membrane increases or the charge barrier of the filtration membrane is disrupted, it can cause an increase in protein in the glomerular filtration fluid. When the urine routine test is negative for urinary protein in the early stage of glomerular disease, the content of urinary microalbumin can change. As the degree of renal damage in glomerular disease increases, the content of urinary microalbumin increases accordingly.
(3) Endogenous creatinine clearance rate (Ccr): Ccr is another endogenous biomarker for evaluating renal function, which can be collected 24 hours of urine and calculated using the following formula: Endogenous creatinine clearance rate (ml/min)=[Urinary creatinine (μ mol/L) x Urine volume (ml)]/[Serum creatinine (μ mol/L) x 1440min]. However, due to the potential for errors and overestimation of renal function in collecting 24-hour urine samples, other formulas (such as Cockcroft Gauh formula, MDRD formula, and other modified formulas based on the test subject) are used to directly estimate glomerular filtration rate (eGFR) from SCr values.
The above are common test indicators of chronic kidney disease. If you have one or more of the following conditions, you should carry out relevant examinations in a timely manner:
Patients with chronic diseases such as hypertension and diabetes need to carry out relevant examinations regularly.
Age over 60 years old requires relevant examinations to evaluate kidney function.
There is a history of urinary system infection, stones, etc., and relevant examinations are needed to evaluate the extent of kidney damage.
Unknown causes of discomfort such as anemia, fatigue, nausea, etc. require relevant examinations to rule out other diseases such as chronic kidney disease.
In short, timely detection and treatment of chronic kidney disease are very important. By conducting relevant examinations, kidney damage can be detected early and appropriate treatment measures can be taken.