Understand the three common indicators for evaluating renal function in one article

Renal function refers to the ability of the kidneys to excrete metabolic waste and maintain the stability of electrolytes such as sodium, potassium, and calcium in the body and the acid-base balance. Serum creatinine, urea nitrogen, and blood uric acid are three commonly used clinical indicators for evaluating renal function. Today, we will explain the clinical significance of these three indicators.

Serum creatinine

Serum creatinine is a product of muscle metabolism and needs to be excreted from the body. When the glomerular filtration function is normal, most of the creatinine will be filtered and excreted, and only a small amount will remain in the blood. Therefore, the concentration of serum creatinine can reflect the condition of renal damage to a certain extent [1]. The normal value of serum creatinine for men is 54~106 μmol/L, and for women it is 44~97 μmol/L.

Clinical significance of serum creatinine: (1) Elevated serum creatinine can be seen in acute and chronic glomerulonephritis, acute and chronic renal failure, uremia, myocarditis and muscle damage. (2) It is more meaningful to measure urea nitrogen and creatinine at the same time. If both are elevated, it indicates serious kidney damage. (3) A decrease may indicate progressive renal atrophy, leukemia and anemia.

Blood urea nitrogen

Blood urea nitrogen refers to a nitrogen-containing compound in plasma other than protein, which is excreted from the body through glomerular filtration. Urea nitrogen will increase when renal insufficiency is decompensated, so it is clinically used as an indicator to judge glomerular filtration function. The normal value of urea nitrogen is 3.2~7.1 mmol/L for adults and 1.8~6.5 mmol/L for infants.

Clinical significance of blood urea nitrogen: (1) Elevated urea nitrogen levels can be seen in various renal parenchymal lesions, such as glomerulonephritis, interstitial nephritis, acute or chronic renal failure, polycystic kidney disease, etc. Renal space-occupying and destructive lesions can also increase blood urea nitrogen. If extrarenal factors can be ruled out, urea nitrogen is also one of the criteria for diagnosing uremia. (2) It is more susceptible to the influence of diet and renal blood flow. For example, infection, intestinal bleeding, hyperthyroidism, etc. can increase blood urea nitrogen levels. In the case of severe dehydration and other conditions where blood volume is insufficient and renal blood flow is reduced, urea nitrogen increases significantly and can decrease on its own after volume supplementation. (3) Acute infectious diseases, high fever, high-protein diet, etc. can also cause an increase in blood urea nitrogen.

Under normal circumstances, the ratio of blood urea nitrogen to blood creatinine is about 1: 10. A high-protein diet, a high catabolic state, dehydration, renal ischemia, hypovolemia, and some acute glomerulonephritis can increase the ratio, while a low-protein diet and liver disease can reduce the ratio.

Serum uric acid

Uric acid is a metabolite in the human body and is excreted by the kidneys. Under normal circumstances, the amount of uric acid produced in the human body each day is equal to the amount of uric acid excreted, so the uric acid content in the human body is relatively stable. The normal value of uric acid is 149-416 μmol/L for men and 89-357 μmo1/L for women.

Increased uric acid levels are mainly seen in: (1) Excessive uric acid production, which can be caused by certain enzyme defects in the purine metabolism process, or excessive uric acid production raw materials in the body, such as myeloproliferative diseases, acute and chronic leukemia, hemolytic anemia, or tumor chemotherapy causing massive cell proliferation and destruction in the body, increased intracellular nucleic acid decomposition, etc. (2) Uric acid excretion disorders. Reduced uric acid excretion due to renal insufficiency and renal tubular diseases can also lead to hyperuricemia [2].

References:

[1] Li Jinlong. What is the clinical significance of elevated creatinine? [J]. Healthy Life, 2022(07):27.

[2] He Yafeng, Li Haibin, Song Bofeng. Analysis of the relationship between serum uric acid and renal function in patients with diabetic nephropathy and hyperuricemia[J]. Guizhou Medicine, 2021, 45(12): 1905-1906.