Some patients go to the doctor because of symptoms such as edema and fatigue; some patients go to the doctor because of abnormal physical examination findings; but more patients with kidney disease do not know that they have kidney disease, thus ignoring the existence of kidney disease for a long time.
There are no obvious symptoms of discomfort in the early stages of kidney disease, but when discomfort occurs, most of them are not early. However, no matter how deep the kidney disease is hidden, some tests will also make it "show the horse's feet".
People with diabetes, hypertension, recurrent infections, hyperuricemia, autoimmune diseases and the elderly are at high risk of kidney disease, and if they do kidney disease-related examinations regularly, they can be detected and treated early to avoid tragedy.
So what tests should be done to see if there is kidney disease? How can I understand the inspection report?
In general, 3 levels of examination are required to determine whether there is kidney disease. The first level: it is also the most basic test, including urine test, renal function test and kidney ultrasound test. The second level: estimation or ECT measurement of glomerular filtration rate (GFR), CT renal angiography, immune-related indicators, etc. Third level; renal biopsy (renal puncture).
Urine test
Urine tests include urine routine tests, urine protein/creatinine ratio tests, quantitative urine protein tests, and urine phase contrast microscopy.
Urine routine examination mainly looks at whether there is proteinuria and hematuria, of course, the urine routine examination of diabetic patients can also find whether there are urine glucose and urine ketone bodies.
Proteinuria and hematuria are early and clear markers of kidney disease. Mild proteinuria and hematuria are not felt, and the naked eye can not see the problem with the urine, and can only be detected through a urine test. However, foam is generally present in large amounts of proteinuria, similar to "hops" in severe cases; in severe hematuria, the urine will become like meat wash or even blood urine.
Urine routine tests mainly include the following:
proteinuria
One of the "proteins" in the urine routine examination is to check the protein in the urine. If the result is (-), it means that the urine protein is negative and there is no proteinuria. If the result is (+), it means that the urine protein is positive and there is urine protein. And the more "+", the more serious the urine protein.
Figure 1 Urinalysis checklist
However, routine urine tests are insensitive and prone to "false negatives", that is, trace amounts of urine protein also show negative urine protein.
In recent years, the urine microprotein/creatinine ratio test is the most sensitive indicator of urine protein, and only trace protein in the urine can be detected in early kidney damage. Random urine is also taken as a specimen, urine trace protein and urine creatinine are detected, and then the ratio is calculated.
Normal value: urine protein/urine creatinine < 30 mg/g;
Microproteuria: urine protein/urine creatinine 30~300mg/g;
Dominant proteinuria: urine protein/urine creatinine > 300 mg/g.
If the urine routine test finds more "+", a quantitative urine protein test should also be done. Leave the urine for 24 hours, measure the content of urine protein, and thus calculate the 24-hour urine protein excretion, the normal value is that the urine protein quantity does not exceed 0.15g/24h.
In general, the amount of urine protein quantification can reflect the severity of kidney disease, which is the gold standard for diagnosing nephrotic syndrome, and is also an important basis for judging the condition and efficacy.
Urine protein quantitative > 0.15g/24h is abnormal;
Urine protein quantification < 0.5 g/24 h for mild proteinuria;
Urine protein quantification of 0.5 to 3.5 g/24 h is moderate proteinuria;
Urine protein quantification > 3.5 g/24 h for a large amount of proteinuria.
The advantage of urine protein quantification is that it can be quantified and is more accurate, which is the gold standard for judging proteinuria. The disadvantage is that the operation is more troublesome, and if the urine output is provided inaccurately, it directly affects the test results. And less sensitive, small amounts of proteinuria may not be detectable.
haematuria
The definition of hematuria is: urine sediment is microscopic examination, if the number of red blood cells per high magnification field of view (HP) under the microscope > 3, it is hematuria.
Figure 2 Urinalysis
There is also an indicator of "urine occult blood" in the urine routine examination, which is the most likely indicator of "stepping on the pit", and many people come to the clinic because the urine test finds "urine occult blood" positive.
Positive urine occult blood does not equal hematuria. If the definition of hematuria is not met, neither the urine occult blood is a few "+" is not hematuria. Once it is clear that it is hematuria, it is necessary to trace where the red blood cells come from, whether they come from the kidneys or extrarenal? This requires "urine phase contrast microscopy".
Urinary phase contrast microscopy is also to take urine sediment as a specimen to observe the morphology of red blood cells. Red blood cells from the kidneys, due to the squeezing of the glomerular filtration membrane, red blood cells often lose their normal form and become ring-shaped, target-shaped, sporangial or shrunken, called malformed red blood cells.
If most of the red blood cells in the urine are malformed red blood cells, and the number of malformed cells >60%, it can be considered that the red blood cells come from the kidneys, called renal hematuria, which is common in glomerulonephritis (especially IgA nephropathy), hypertensive kidney disease, purpura nephritis and other nephropathy.
Figure 3 Urine test
If most of the red blood cells in the urine are normal, and the number of malformed red blood cells is less than 60%, it means that the red blood cells are not squeezed by the glomerular filtration membrane, but come from outside the kidney, called extrarenal hematuria. It is common in extrarenal diseases such as urinary tract infections, ureteral stones, renal tuberculosis, renal tumors, and trauma.
Kidney function
Renal function indicators mainly include blood creatinine, urea nitrogen and blood uric acid, of which the key indicators are blood creatinine.
Both blood creatinine and urea nitrogen are metabolic wastes of proteins, blood uric acid is the metabolic waste of nucleic acids, and all three are metabolic wastes of meat. In general, the protein content in the human body is relatively fixed, and the change in eating habits is not large, so the daily production of the three is also relatively fixed.
After the blood uric acid is filtered through the glomeruli, the renal tubules are also reabsorbed and re-secreted, so there are many factors that affect the level of blood uric acid. After blood creatinine is filtered through the glomeruli, the renal tubules will not reabsorb and re-secrete, and the filtration ability of the glomeruli (that is, renal function) directly affects the level of blood creatinine.
Blood creatinine
If the kidneys function normally, even if they produce more creatinine per day, the kidneys will excrete them and maintain the serum creatinine value at normal levels. If kidney function declines and the kidneys are unable to effectively excrete creatinine from the body, then serum creatinine rises. In general, elevated serum creatinine means decreased kidney function.
Figure 4 Serum test sheet
Elevated serum creatinine indicates that the kidney function is not normal, the elderly serum creatinine is normal, and the kidney function may have declined, which will be mentioned below in the GFR content.
Cystatin C
Cystatin C, the full name cysteine protease inhibitor C, was first reported in 1985 as an indicator of renal function, but it has only been gradually widely used in clinical practice in recent years.
Cystatin C is a small molecule protein that is mainly found in the blood. The rate of production is stable, and the amount of production is independent of gender, age, muscle mass, and is not easily affected by other factors.
The kidney is the only excretory organ, which is no longer reabsorbed by the renal tubule after glomerular filtration, and other pathological factors have little effect on its excretion. Therefore, cystatin C content is considered an ideal indicator to assess kidney function.
Kidney color ultrasound
The kidneys are like a pair of erect broad beans, located opposite the waist. In general, normal people have 10 cm long kidneys and 1.5 cm thick in the renal cortex (mainly glomeruli).
If the kidneys are enlarged, they are seen in diseases such as renal edema, early diabetes, polycystic kidneys, or renal cysts; if the kidneys are smaller than 9 cm, or if the renal cortex is thinner (less than 1.3 cm), it is seen in the middle and advanced stages of various chronic kidney diseases (CKD), at this time most glomerular sclerosis, elevated serum creatinine, and moderate to severe renal failure.
If the difference in the size of the two kidneys exceeds 1 to 1.5 cm, the narrowed kidney shrinks, which is more common in diseases such as renal artery stenosis and congenital renal dysplasia.
Figure 5 Renal color ultrasound
Congenital renal dysplasia, with small kidneys on one side and compensatory enlargement on the contralateral kidneys. Renal artery stenosis, especially atherosclerotic renal artery stenosis, renal ischemia atrophy, ischemic one side of the kidney is significantly reduced, while the contralateral kidney is normal or mildly reduced.
Renal color ultrasound can also detect congenital renal dysplasia, renal cysts, renal tumors, kidney and ureteral stones.
Renal CT tests have higher resolution, but the cost is also high, so it is not as popular as kidney color ultrasound.
GFR
Blood creatinine is mentioned above as an indicator of kidney function. However, the production of blood creatinine is easily affected by many factors such as age, sex, body shape, height, muscle mass and dietary structure, and does not truly reflect the level of kidney function.
For example, the muscles of the elderly will atrophy, the metabolism will slow down, the amount of meals will also decline, the amount of creatinine produced every day is not much, even if the kidney function is significantly reduced, the blood creatinine value will not be too high. And a fitness, especially a young person who takes muscle-building products at the same time, produces a large amount of creatinine every day, and the kidney function is normal and the blood creatinine may also be mildly elevated.
Therefore, normal blood creatinine in the elderly does not mean that kidney function is normal; while the mild elevation of blood creatinine in young people may not have decreased kidney function, but long-term excessive fitness, muscle gain, kidney function may not be guaranteed.
Therefore, professionally assessing kidney function mainly depends on GFR. GFR is also the only criterion for staging the severity of kidney disease, and the stages of CKD we are talking about are divided by GFR.
Stage CKD1: GFR> 90 ml / min (normal renal function);
CKD2期：GFR 60-89ml/min；
CKD3期：GFR 30-59ml/min；
CKD4 stage: GFR 15-29ml/min, which is colloquially known as severe renal failure;
CKD5: GFR
There are two ways to get a GFR
1. Calculation method
According to the level of serum creatinine, combined with the patient's gender, age, weight and other factors, to calculate the glomerular filtration rate, called estimating the glomerular filtration rate. Computers or mobile phones have ready-made calculation formulas, without hard memorization, the indicator can be directly entered to get the results.
In recent years, the Global Renal Disease Prognosis Organization (KDIGO) has proposed to use calculation formulas based on blood creatinine and cystatin C, such as the CKD-EPI formula, to estimate the glomerular filtration rate.
2. Machine measurement
At present, the most commonly used is to use ECT for renal function imaging, one is accurate, is regarded as the gold standard for determining kidney function, and the other is that the kidney function of the two kidneys can be determined separately.
Figure 6 Renal function phenomena
CT renal angiography
If one kidney is found to be atrophied, or there is coronary artery stenosis and multiple arterial stenosis throughout the body, or other evidence of suspected renal artery stenosis, CT angiography can be done, similar to CT coronary angiography.
CT renal angiography can determine whether there is renal artery stenosis and the degree of stenosis, and decide whether to take treatment such as renal artery stent therapy.
Examination of immune-related indicators
The kidneys are particularly susceptible to attack by the autoimmune system, and common autoimmune diseases such as systemic lupus erythematosus, systemic small-vesselritis, rheumatism and rheumatoid arthritis, ankylosing spondylitis, etc., can cause kidney damage.
Therefore, after the discovery of proteinuria, anti-phospholipase A2 receptor antibodies, rheumatism three, autoantibodies, immunoglobulins, ANCA, erythrocyte sedimentation rate and other tests should be done to clarify the cause and differential diagnosis.
Renal histopathological examination
For urine protein quantification of more than 1g/24h, or unexplained kidney damage, etc., in order to determine the diagnosis, determine the cause, determine the treatment measures and determine the prognosis, etc., renal biopsy examination, including optical microscopy, immunofluorescence microscopy and electron microscopy.
A kidney biopsy is the gold standard for diagnosing kidney disease. Although renal puncture has a "hammer-and-hammer" effect on determining the diagnosis of kidney disease, deciding on treatment plans, and assessing prognosis, the biggest resistance to renal puncture comes from patients' misunderstandings, such as worrying about pain and worrying about kidney damage. The pain is just the pain of the needle when you take a local anesthetic.
There are a total of 2 million to 2.4 million glomeruli in both kidneys, and about 30 glomeruli are generally removed by renal puncture. For more than 2 million, 30 will not affect the capacity of the sea, just as the sea will not affect the capacity of the sea, just as it will not cause hypotension and anemia when blood is drawn.
For kidney disease, early detection, early diagnosis, and precise treatment are the most effective measures to avoid the aggravation of kidney disease.
Source: Nephropathy Channel of the Medical Professions
Edited by: Yeah Reviewer: Xiao Ran