How to check kidney function? Do you know these methods?

Sudden onset of back pain may be due to problems with kidney function. In this case, endogenous creatinine clearance test, blood urea nitrogen and blood creatinine determination, phenol red (PSP) excretion test and other methods can be used for examination, with a relatively high accuracy rate.

1. Endogenous creatinine clearance test

This is more common when kidney function tests measure the degree of glomerular damage. Before and on the day of the test, the subjects were fed a low-protein diet for three days, and no meat was eaten and strenuous exercise was avoided. The subjects urinated completely at 8 a.m. on the test day, and then collected the urine in a clean container containing toluene as a preservative for 24 hours until 8 a.m. the next morning. On the test day, 2-3 ml of venous blood was drawn. Send blood and urine for examination at the same time. The normal range is 109~148 L/24 hours (or 80~120 ml/minute), and the average value is 128 L/24 hours (or 100 ml/minute). A clearance rate less than 80% of the normal value indicates impaired glomerular filtration function. A clearance rate of 70-51 ml/min is considered slightly reduced, 50-31 ml/min is considered moderately reduced, and less than 30 ml/min is considered severely reduced. A clearance rate of 20-11 ml/min indicates early-stage renal insufficiency, 10-6 ml/min indicates late-stage renal insufficiency, and less than 5 ml/min indicates end-stage renal insufficiency.

2. Blood urea nitrogen and blood creatinine determination

This is a commonly used test for renal function. Take 1 ml of venous blood, inject it into an anticoagulant tube, and mix it thoroughly. Normal blood urea nitrogen is 9~20 mg/L and blood creatinine is 1~2 mg/L. Various serious kidney diseases cause renal insufficiency and the level of all proteins increases. Upper gastrointestinal bleeding, severe infection and excessive protein in the diet can all cause a temporary increase in blood urea nitrogen. Blood creatinine concentration is less affected by factors such as diet. When it is significantly elevated, it indicates a poor prognosis.

3. Phenol red (PSP) excretion test

Do not use aspirin, penicillin or other drugs before the test. Diuretic beverages such as tea and coffee should be avoided before and during the test. Instruct the patient to urinate 20 minutes before the test, then drink 300-400 ml of water, and no longer drink water. Use a 1 ml syringe to accurately draw 1 ml of 0.6% phenol red solution and inject it intravenously. Collect urine once at 15, 30, 60, and 120 minutes after injection, collect them into clean specimen bottles, and send them for testing in time. Normally, the excretion rate is 25% or higher 15 minutes after injection, and the total excretion rate is greater than 55% in 120 minutes. If it is lower than the normal value, it indicates renal damage. Diseases that can cause changes in renal blood flow, such as heart failure, severe hypertension and pyelonephritis, will also reduce the excretion rate of phenol red.