Kidney function tests

The kidneys are important organs in the human body. They secrete urine and help excrete waste. If there is a problem with the kidneys, waste in the body cannot be excreted with urine, and various conditions will occur in the body. Therefore, we must protect our kidneys and allow them to work normally to ensure the normal functioning of the body and ensure the health of the body.

Generally, kidney function is checked through blood and urine. When checking blood, you must follow the doctor's instructions. If there are items that you cannot eat, you must not eat, so as not to affect the test results. When checking urine, you must urinate in a clean container and avoid urine contamination to ensure the accuracy of the test results. When doing a kidney function test, many people do not know what items need to be checked. Let us introduce them below.

Inspection items

1. Blood urea nitrogen (BUN)

Reference value: Normal situation: diacetyl-oxime colorimetric method 1.8～6.8mmol/L, urease-natrium colorimetric method 3.2～6.1mmol/L.

Clinical significance: Increased: acute and chronic nephritis, severe pyelonephritis, acute and chronic renal dysfunction caused by various reasons, heart failure, shock, massive internal bleeding, burns, dehydration, adrenal cortex insufficiency, prostate hypertrophy, chronic urinary tract obstruction, etc.

2. Serum creatinine (Scr)

Reference value: Normal situation: Adult male 79.6～132.6μmol/L, female 70.7～106.1μmol/L, children 26.5～62.0μmol/L, whole blood 88.4～159.1μmol/L.

Clinical significance: Increase: renal failure, uremia, heart failure, gigantism, acromegaly, salicylate treatment, etc. Reduce: progressive muscular atrophy, leukemia, anemia, etc.

3. Blood urea

Reference value: Normal situation: 3.2～7.0mmol/L.

Clinical significance: Increased levels indicate acute and chronic nephritis, severe pyelonephritis, acute and chronic renal dysfunction caused by various reasons, heart failure, shock, burns, dehydration, massive internal bleeding, adrenal cortex insufficiency, prostatic hypertrophy, chronic urinary tract obstruction, etc.

4. Serum uric acid

Reference value: Normal situation: Adult male 149～417μmol/L, female 89～357μmol/L; Male >60 years old 250～476μmol/L, female 190～434μmol/L.

Clinical significance: Increase: gout, acute and chronic leukemia, multiple myeloma, pernicious anemia, renal failure, liver failure, polycythemia, pregnancy reaction, strenuous activity and after high-fat meal, etc.

5. Urine creatinine (Cr)

Reference value: Normal situation: infants 88 ~ 176μmmol·kg-1/d; children 44 ~ 352μmol·kg-1/d; adults 7 ~ 8mmol/d.

Clinical significance: Increased in: hunger, fever, acute and chronic wasting diseases, after strenuous exercise, etc. Reduction: renal failure, muscular atrophy, anemia, leukemia, etc.

6. Urine protein

Reference value: Normal: Qualitatively negative

Clinical significance: Normal people excrete about 40 to 80 mg of protein in urine every day, with an upper limit of no more than 150 mg, mainly albumin, followed by glycoproteins and glycopeptides. About 0.60 (60%) of these proteins come from plasma, and the rest come from secretions of the kidneys, urinary tract, and prostate, and tissue decomposition products, including urease, hormones, antibodies and their degradation products. Physiological increase: postural proteinuria, exercise-induced proteinuria, fever, emotional excitement, excessively cold or hot climate, etc.

7. Selective Proteinuria Index (SPI)

Reference value: Normal situation: SPI < 0.1 indicates good selectivity; SPI 0.1-0.2 indicates average selectivity; SPI > 0.2 indicates poor selectivity.

Clinical significance: When the amount of large molecular IgG excreted in urine is small, it indicates good selectivity. On the contrary, it indicates poor selectivity.

8. β2-microglobulin clearance test

Reference value: Normal: 23～62μl/min

Clinical significance: Increased: renal tubular damage. This test is a reliable indicator of the extent of renal tubular damage and is particularly helpful in identifying patients with mild disease.

9. Urea removal rate

Reference values ​​under normal conditions: standard clearance value 0.7～1.1ml·s-1/1.73 m2 (0.39～0.63ml·s-1/m2) maximum clearance value 1.0～1.6ml·s-1/1.73 m2 (0.58～0.91ml·s-1/m2).

For clinical significance, see inulin clearance. Corrected clearance value for children = 1.73/child’s body surface area × actual clearance value. The body surface area of ​​children is very different from that of adults. The correction formula is: maximum clearance value = 1.73/child’s body surface area × actual clearance value.

10. Blood endogenous creatinine clearance

Reference value: Normal situation: Plasma in general adults 0.80 ~ 1.20ml · s-1 / m2, urine adult male 0.45 ~ 1.32ml · s-1 / m2, female 0.85 ~ 1.29ml · s-1 / m2. For those over 50 years old, it decreases by 0.006ml · s-1 / m2 each year.

When the endogenous creatinine clearance rate drops to 0.5-0.6 ml·sl/m2 (52-63 ml/min/1.73 m2), it means glomerular filtration function is impaired. If it is <0.3 ml·s-1/m2 (31 ml/min/1.73 m2), it means glomerular filtration function is severely impaired. Note: In the late stages of chronic nephritis or other glomerular diseases, the excretion of creatinine by the renal tubules increases accordingly, making the measured results higher than the actual ones. Similarly, in patients with chronic nephritis nephrotic type, due to the increased permeability of the tubular basement membrane, more endogenous creatinine is excreted from the renal tubules, and the measured value also increases accordingly.

11. BUN/creatinine ratio (BUN)

Reference value: Normal situation: 12:1～20:1

Clinical significance: Increased: decreased renal perfusion (dehydration, hypovolemic shock, congestive heart failure, etc.), obstructive urinary tract lesions, high-protein meals, hypercatabolic state, glomerular lesions, use of glucocorticoids, etc. Reduced: Acute tubular necrosis.

12. Phenol red (phenolsulfone) excretion test (PSP)

Reference value: Normal situation: 15min0.25～0.51(0.53) 30min0.13～0.24(0.17) 60min0.09～0.17(0.12) 120min0.03～0.10(0.06) Total amount of 120min0.63～0.84(0.70).

Clinical significance: When renal tubular function is impaired by 0.50 (50%), the PSP excretion rate begins to decrease. Reduce: chronic glomerulonephritis, chronic pyelonephritis, renal vascular sclerosis, Fanconi syndrome, heart failure, shock, severe edema, late pregnancy, urinary tract obstruction, bladder insufficiency, etc.

We all know the relevant content of kidney function test, so try to drink less water before the test to avoid a decrease in blood and urine concentrations. Female friends should try not to check urine during menstruation, as menstrual blood entering the urine will also affect the test results, so everyone must pay attention.