Overview of renal function tests: core items and clinical significance

Renal function test is a key means to evaluate the health status of the kidneys, mainly includingUrine analysis, blood biochemical indicators and imaging examinationsThree major categories. Among them, serum creatinine (Scr), urea nitrogen (BUN), and glomerular filtration rate (eGFR) are core blood indicators, reflecting the kidney's filtration function; urinary protein and urinary microalbumin are used for early kidney injury screening. Secondary items include electrolyte (such as blood potassium, blood calcium) and acid-base balance testing to help determine the kidney's regulatory ability. Imaging studies such as ultrasound or CT can detect structural abnormalities in the kidneys. The examination results need to be comprehensively interpreted in conjunction with clinical symptoms to avoid misjudgment by a single indicator.

Blood biochemistry test: "barometer" of kidney function

Blood tests are a core part of kidney function assessment.Serum creatinineIt is a muscle metabolite, and its elevated level often indicates a decrease in glomerular filtration function;Urea nitrogenAffected by protein intake and liver metabolism, it needs to be combined with creatinine analysis. More accurateEstimated glomerular filtration rate (eGFR)Calculated through age, gender, and creatinine value, it directly reflects the working efficiency of the kidneys. For example, eGFR <60 mL/min/1.73m² for 3 months can be diagnosed as chronic kidney disease. Some hospitals also test cystatin C (Cys C), which is more sensitive to early renal damage.

Urine test: early warning sign of kidney damage

Urinalysis can detect early kidney disease.Urine routineAbnormalities such as protein, red blood cells, and casts may indicate nephritis or nephrotic syndrome;Urinary microalbumin/creatinine ratio (UACR)It is the gold standard for diabetic nephropathy screening, and 30-300 mg/g is the microalbuminuria stage. A 24-hour urine protein quantification >3.5 g is consistent with the diagnosis of nephrotic syndrome. In addition, special items such as urine osmotic pressure and urinary NAG enzyme can further locate renal tubular damage. When collecting morning urine or 24-hour urine specimens, contamination must be avoided to ensure accurate results.

Imaging and other auxiliary examinations: a "perspective" of kidney structure

When laboratory indicators are abnormal, imaging examinations can determine the cause.Kidney ultrasoundNon-invasive and economical, capable of detecting stones, cysts or atrophy;CT/MRIHigher resolution for tumors or vascular lesions. In a few cases, a kidney biopsy is required to diagnose the type of nephritis through pathology. In addition,Renal nuclide scan (such as GFR measurement)It can quantify renal function and guide surgical decisions. Patients with hypertension need to detect the activity of the renin-angiotensin system to identify renal hypertension.

Comprehensive interpretation and precautions

Renal function tests require dynamic observation, as a single abnormality may be interfered by dehydration, infection, etc. Patients with chronic kidney disease should regularly monitor eGFR and urinary protein, and adjust their medication regimen (such as ACEI drugs). High-protein meals and strenuous exercise need to be avoided 3 days before the examination. At present, mainstream testing equipment includes Roche Cobas series, Siemens ADVIA biochemical analyzer, etc., and reagent brands include Beckman, Abbott, etc. If the results are abnormal, it is recommended that a nephrology specialist follow up and develop intervention measures based on clinical manifestations.

Quote sources:
1. "Chinese Guidelines for the Prevention and Treatment of Chronic Kidney Disease (2023 Edition)" - Nephrology Branch of the Chinese Medical Association
2. US NKF-KDOQI Clinical Practice Guidelines (2021)
3. Testing equipment: Roche Cobas c501 biochemical analyzer, Siemens Atellica solution
4. Expert opinion: Professor Wang Haiyan (Department of Nephrology, Peking University First Hospital)’s discussion on early kidney injury screening