The significance of tests to evaluate kidney function

This is an automatically translated article.

The article was professionally consulted with MSc Do Thi Hoang Ha - Doctor of Biochemistry, Laboratory Department - Vinmec Hai Phong International General Hospital.
The kidneys are an important organ of the urinary system, whose main function is to form urine, filter, reabsorb and excrete substances from the blood, and also have hormone functions as well as participate in the regulation of water balance. electrolytes and acid-base balance. Kidney function is assessed through blood tests, urine or imaging tests,... Patients are often ordered to perform a combination of tests to most accurately assess kidney function.

1. Blood biochemical tests

1.1 Blood urea test Urea is a product of the body's protein degradation, which are exogenous proteins that are converted into amino acids by the proteases of the digestive tract, then further converted and finally into CO2 and NH3. Urea always exists in the blood, is filtered through the glomeruli and eliminated from the body through urine. Urea blood tests are used to evaluate kidney function and monitor kidney diseases. Renal function index is normal if the blood urea value ranges from 2.5 to 7.5 mmol/l.
Blood urea increases when the diet contains too much protein or in the case of diseases such as glomerulonephritis, nephritis, kidney stones, kidney failure, ureteral stones, dehydration due to high fever, diarrhea, gastrointestinal bleeding chemistry, congestive heart failure,... Blood urea is reduced in pregnant women or when the patient eats less protein, liver function decline, fluid infusion,...
1.2 Serum Creatinine Test Creatinine is a product As a result of the breakdown of creatinine in the muscles, it is excreted by the kidneys and the kidneys maintain creatinine in the blood at a constant concentration, so the concentration of creatinine accurately reflects the filtering function of the kidneys.
Normal creatinine values ​​for men are 0.6 -1.2 mg/dl or 53-106 umol/l (SI units) and women are 0.5 - 1.1 mg/dl or 44-97 umol/l (SI units) ). When blood creatinine levels are high, it means kidney dysfunction. The reason is because when kidney function declines, the ability to filter creatinine will decrease, leading to higher-than-normal blood levels of this substance.
Creatinine index in renal failure increases with each grade of renal failure. According to the American Kidney Foundation (NFK), there are 5 levels of kidney failure based on glomerular filtration rate (calculated based on blood creatinine).
Creatinine index less than 130 mmol/l - kidney failure grade I, Creatinine index 130 - 299 mmol/l - kidney failure grade II Creatinine index 300 - 499 mmol/l - kidney failure grade IIIa, Creatinine index 500 - 899 mmol/l - grade III kidney failure b, Creatinine index over 900 mmol/l - grade IV renal failure.

1.3 Electrolytes Renal dysfunction causes an imbalance of electrolytes in the body. Specifically:
Sodium (Sodium): Normal blood sodium ranges from 135 - 145 mmol/L. Sodium levels are needed to maintain fluid and acid-base balance and for neuromuscular function. Healthy kidneys change the way they excrete sodium in the urine to prevent hypernatremia. A person with kidney failure may not be able to excrete as much sodium as usual, thus causing hypernatremia, which is associated with symptoms such as: disorientation, muscle twitching, increased blood pressure.. Potassium (Potassium): Normal blood potassium is 3.5-5.1 mmol/L. The kidneys are primarily responsible for excreting potassium from the body and varying the extent of potassium excretion according to the current concentration in the blood. A person with kidney failure may not be able to excrete as much potassium as usual, which can potentially cause hyperkalemia. Hyperkalemia is associated with symptoms such as abdominal pain, fatigue, muscle weakness, paralysis, cardiac arrest.. Magnesium (Blood magnesium): Normal human blood magnesium is 0.7 – 0.95 mmol/L Similar to Thus, kidney failure can also cause increased levels of magnesium in the blood due to not excreting enough electrolytes. Hypermagnesemia is associated with symptoms such as: low blood pressure, decreased heart rate, cardiac arrest.. Blood calcium: blood calcium in healthy people is 2.2-2.6 mmol/L. There is a reciprocal relationship between phosphorus and calcium, and levels of both of these electrolytes can be affected by kidney failure. Renal failure causes hypocalcemia with increased phosphate, which can lead to phosphorus retention and decreased blood calcium levels. Hypocalcemia is associated with symptoms such as: muscle spasms, convulsions, arrhythmias, heart failure.. 1.4 Acid-base balance test This is a kidney function test usually ordered by a doctor. for people with suspected kidney disease. Normally, blood pH is maintained at 7.37 - 7.45 to ensure optimal functioning of cellular enzymes, clotting factors and muscle contraction proteins. Kidney failure will reduce acid excretion in the process of metabolism or cause bicarbonate loss, increasing acid levels in the blood and organs in the body.

1.5 Blood uric acid test This is a test used to diagnose gout, identify joint diseases (arthritis, arthralgia..), kidney diseases (renal colic, hydronephrosis, kidney failure...) Normal uric acid concentration in the blood of men is 180 - 420 mmol/l, women are 150 - 360 mmol/l. Blood uric acid increases in people with kidney failure, gout, psoriasis, acute leucemie, lymphoma, hemolytic anemia, lactic acidosis, congestive heart failure..
1.6 Some other tests Serum albumin: is a protein that plays an important role in metabolism and metabolism. Normally, the serum albumin index is 35 - 50 g/L, accounting for 60 - 80% of the total protein in the blood. Blood albumin decreases when the albumin production function of the liver is inhibited, because albumin is broken down a lot or excreted in the urine (acute glomerulonephritis such as acute glomerulonephritis...) include albumin and blood globulins. Normal blood protein index is 60-80 g/L. People with kidney disease often have reduced total protein due to damaged glomerular membranes. Complete blood count: Patients with chronic renal failure often have a decreased red blood cell count.

2. Urine test

2.1 Total urinalysis Urinalysis: Normal urine density is 1.01 - 1.020. Early renal failure can reduce urine concentration, leading to decreased urine density. In case of suspected kidney disease, the patient may be ordered to perform additional tests such as urine concentration test, urine dilution test, day and night urine density comparison, ... Protein: the total urinalysis sample has the presence of protein, the doctor will assign the patient to perform an additional 24-hour proteinuria quantitative test if necessary.

2.2 Quantification of 24-hour proteinuria (urine protein) Protein in urine in healthy subjects is 0.05 - 0.08g/l/24h (resting mode) and <0.3g/l/24h in exercise regimen sport exercise. In people with glomerulonephritis, acute glomerulonephritis, renal failure, systemic diseases affecting the kidneys (diabetes, lupus erythematosus, hypertension), ... often have increased proteinuria. above 0.3g/l/24h.

3. Diagnostic Imaging Tests

3.1 Abdominal ultrasound Helps to detect hydronephrosis due to ureteral obstruction. If the patient's kidneys have bilateral hydronephrosis, it can cause acute kidney failure or chronic kidney failure, detect congenital and hereditary polycystic kidney disease. Ultrasound image shows small kidney size, structural changes, many cysts or loss of cortical differentiation,... suggestive of chronic kidney disease. In addition, ultrasound can also help detect kidney stones or tumors in the kidneys.
3.2 Abdominal CT Scan Is a method that uses X-rays to probe images, allowing doctors to clearly see the entire urinary system. Abdominal CT scan is usually only used in cases of suspected renal failure due to urinary tract obstruction. Contrast-enhanced CT scan using a multi-slice scanner can visualize the entire urinary tract, helping doctors discover the location and cause of ureteral obstruction.
3.3 Radioisotope renal scintigraphy Is the only test that allows the assessment of renal function on each side. This method helps the doctor see clearly the filtering function of each kidney, the percentage of perfusion and participating in the function of each kidney. In addition, if a diuretic injection test is done, this test method also helps the doctor evaluate the degree of bilateral ureteral obstruction.

4. Indication of kidney function tests

Annual health check: do simple directional tests such as blood biochemistry, urinalysis, complete blood count and abdominal ultrasound. Family history of hereditary kidney diseases or having a close relative with kidney failure: blood chemistry tests, complete blood count, urinalysis, abdominal ultrasound and specific genetic tests are required. . When there are signs of renal failure: blood chemistry tests, urinalysis, complete blood count and abdominal ultrasound should be performed. If other causes of urinary obstruction are found, further imaging tests should be performed. If no obstruction is found, a kidney biopsy may be performed. There is a history of surgical intervention on the urinary tract or abdominal organs: blood biochemical tests, complete blood count, urinalysis and abdominal ultrasound should be performed. If there are signs of urinary obstruction, further imaging tests should be done. Vinmec International General Hospital is one of the hospitals that not only ensures professional quality with a team of leading doctors, modern equipment and technology, but also stands out for its examination and consulting services. and comprehensive, professional medical treatment; civilized, polite, safe and sterile medical examination and treatment space. Customers when choosing to perform tests here can be completely assured of the accuracy of test results.

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