GFR Introduction and Renal Function Tests

During routine physical examinations, many individuals may find the abbreviation "GFR" on their medical reports. As this medical abbreviation is not widely understood, it can often lead to confusion. So, what does GFR mean? GFR stands for glomerular filtration rate, a term frequently used in renal medicine. Elevated glomerular filtration rates are considered abnormal, and if not detected and treated promptly, they may progress to uremia over time. Therefore, it is important to pay close attention to this indicator.

I. Introduction to GFR

Clinically, GFR refers to the glomerular filtration rate. In the staging of chronic kidney disease, glomerular filtration rate is a crucial factor. Normal glomerular filtration rates range from 100ml/min plus or minus 10ml/min. As age increases, glomerular filtration rate decreases by 5-10ml/min for every 10 years of life. When the glomerular filtration rate falls below 30ml/min, serum creatinine levels may rise above normal. Therefore, the residual renal function can be assessed based on the glomerular filtration rate. When the glomerular filtration rate is above 30ml/min, renal function is considered normal, or compensatory. Patients may not have any clinical manifestations. However, when the glomerular filtration rate falls below 30ml/min, serum creatinine levels may rise, accompanied by symptoms such as anorexia, nausea, vomiting, edema, deep breathing, irritability, confusion, and skin rashes.

II. Causes of Elevated Urea in Renal Function Tests

1. Decreased glomerular filtration rate is a common cause. In kidney diseases, the glomeruli may undergo varying degrees of lesion or sclerosis, resulting in a reduction in the effective filtration area and decreased filtration of urea nitrogen from the blood. Consequently, blood urea nitrogen levels may rise during blood tests, often accompanied by elevations in serum creatinine.

2. Increased reabsorption of urea by the renal tubules can also lead to elevated urea nitrogen levels without a corresponding increase in serum creatinine. When urea nitrogen levels are high while serum creatinine remains normal, it is often attributed to insufficient blood volume, medically referred to as pre-renal azotemia. This occurs because the body maintains homeostasis by increasing the reabsorption of urea nitrogen from the original urine when blood volume is insufficient. As urea nitrogen has a smaller molecular weight, many small and medium-sized molecules are reabsorbed and return to the bloodstream. In contrast, creatinine, with a relatively larger molecular weight, is not reabsorbed, resulting in elevated urea nitrogen levels while serum creatinine remains normal. Prolonged pre-renal azotemia can easily lead to acute renal failure.

Elevated urea levels in renal function tests reflect renal function loss and can be indicative of various kidney diseases such as acute and chronic nephritis, nephropathy, uremia, and renal failure. Therefore, it is crucial to prioritize and seek timely treatment.