Many kidney diseases only lead to permanent, irreversible damage to the kidney tissue after many years. In contrast to acute kidney failure, timely treatment can in most cases lead to stabilization or even recovery of kidney function. The patient’s medical history and physical examination play an important role in this process.
For his diagnosis, the doctor needs to know about any pre-existing kidney damage, chronic diseases and the intake of medication. Information about kidney diseases in the family of the affected person is also important.
The measurement of blood pressure and heart rate as well as the condition of the skin and the filling of the neck veins allow conclusions to be drawn about the fluid balance and thus about possible water overload. With a 24-hour blood pressure measurement, the doctor can determine whether a patient has normal blood pressure during the day but suffers from unnoticed night-time high blood pressure. This often occurs in diabetics. A lack of a nightly drop in blood pressure considerably increases the risk of organ damage.
An ultrasound examination can be used to determine the size of the kidney and the condition of the kidney tissue. If the kidneys are very small, this is an indication that the kidney has been damaged for some time.
When the kidneys can no longer filter the blood sufficiently, creatinine and urea accumulate in the blood. The doctor can control this by analyzing blood values. The more creatinine and urea is found in the blood, the weaker the filtering function of the kidneys. The creatinine normal value is 8-12 milligrams per liter of blood, the normal urea concentration in the blood is between 200 and 450 milligrams per liter. As an alternative to creatinine, the cystatin C in the blood is measured as a control value, but this is not yet a routine examination.
The concentration of creatinine in the blood is used in everyday clinical practice for an initial assessment of kidney function. However, this is not very accurate for all people, as the creatinine value often only increases when the kidney function has fallen by almost half. This means that a slight reduction in kidney function can be overlooked.
Better suited for an early diagnosis is the so-called creatinine clearance, which indicates how quickly the kidneys can filter creatinine out of the blood. To do this, urine must be collected for 24 hours and then creatinine is determined simultaneously in the blood and in the urine. A reduced creatinine clearance is found before the creatinine in the blood rises and can therefore indicate early damage to the kidneys. The doctor also calculates the glomerular filtration rate from the creatinine level in the blood serum or another small substance in the blood, cystatin C.
In addition, the physician has the white blood cell count and other blood values determined, such as the C-reactive protein, liver values and fat values. The C-reactive protein is produced in greater quantities during inflammatory processes in the liver and can indicate the course of kidney weakness. Together with the blood count, which shows elevated white blood cells during inflammatory processes, indications of inflammation in the body can thus be found, in addition to the medical history.
The measurement of calcium, phosphate, vitamins and parathormone provides information about a disturbed electrolyte balance and possible damage to the bones.
As there is normally little or no protein in the urine, excretion of protein in the urine is an important indication of the presence of kidney disease. For this purpose, the urine is collected and analyzed for over 24 hours. Alternatively, the doctor can determine the ratio of protein to creatinine in the urine. In a healthy kidney, the filter tissue is so dense that a maximum of 200 milligrams of protein per day are excreted in the urine. Regular measurements of protein excretion are also an important part of monitoring the course of the disease, as more and more protein is detected in the urine as the disease progresses.
A urine rapid test with a test strip allows the doctor to make an initial assessment of kidney disease. The test strips measure the protein content and the blood cells in the urine. If the test result is abnormal, the urine must be further tested for the type and quantity of these proteins and cells.
The so-called glomerular filtration rate (GFR) is another laboratory value that enables the doctor to detect chronic kidney weakness via the urine at an early stage. With its help, he can assess the severity of the disease. The normal value of the glomerular filtration rate for creatinine is 90-130 milliliters per minute. This means that a healthy kidney cleans at least 90 milliliters of blood per minute.
In a microscopic examination of the urine, the so-called urine sediment, the doctor looks for red and white blood cells. If there are indications of damage to the renal corpuscles, it may be necessary to puncture the kidney to remove and examine the tissue.