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There is a humorous comparison about the anatomy of the kidneys: it is a bit like in life – smaller calyxes, larger calyxes and finally the pelvis .. However, other organs of our body depend on the proper functioning of this seemingly simple organ.
It is worth realizing at this point that urine is formed from… blood. Its production in the kidneys is a complicated process, as a result of which the liquid part of blood, plasma, is deprived of excess fluids, electrolytes and unnecessary metabolic products produced throughout the body, as well as substances supplied from outside: toxins, drugs, vitamins and heavy metals. The kidney also helps maintain normal blood pressure – hence the slogan Protect the kidneys, save your heart. In addition, it regulates the production of red blood cells, and by participating in the production of vitamin D, it affects bone metabolism and the proper function of the immune system.
Kidney diseases often develop gradually and are asymptomatic for a long time. Laboratory tests are a useful tool for early detection of abnormalities.
Glomerular filtration rate
Renal failure is manifested by a reduction in the so-called glomerular filtration (glomerular filtration, GFR), technically expressed as the volume of renal filtered plasma per time unit, per standard body surface area (ml / min / 1,73 m2). GFR assessment is helpful, inter alia, in the diagnosis of chronic kidney diseases (CKD). As they progress, this parameter decreases, and its size influences further diagnostic and therapeutic recommendations. GFR can be assessed in several ways.
The most popular is the determination of serum creatinine concentration, accompanied by the calculation of the estimated GFR (eGFR) value. Usually, an increase in creatinine concentration is accompanied by a decrease in GFR, but e.g. in the elderly, filtration may be reduced with normal creatinine levels, and in the early stages of kidney disease, filtration may be normal despite elevated creatinine.
You can also designate the so-called creatinine clearance – illustrating the ability of the kidney to clear the blood of creatinine. For this test, a properly conducted daily urine collection (DZM) is necessary – the determination of creatinine is performed both in the urine sample collected from it and in the blood serum.
A less complicated, but a bit more expensive test is the determination of cystatin C in the blood.
GFR below 3 ml / min / 60 m1,73 for 2 months is the basis for the diagnosis of CKD. In the case of GFR> 60 ml / min / 1,73 m2, chronic kidney disease is diagnosed when imaging tests show abnormalities in the structure and function of the kidneys or abnormalities in the renal function of urine and blood tests, discussed below.
Protein determination in urine
An important indicator of impaired kidney function is the appearance of protein in the urine. This statement is a bit misleading – urine physiologically contains a small amount of protein. In kidney diseases, there is an increased excretion of protein into the urine and / or decreased its reuptake. If it is a sufficiently intense process (protein in the urine above 200 mg / l), it can be detected during the general urine test, which may be accompanied by the presence of rollers in the urine sediment. This condition is called clinical proteinuria. It may indicate serious diseases, such as diabetic nephropathy, glomerulonephritis or toxic nephritis, and ultimately may lead to the so-called nephrotic syndrome. Further diagnostics in the case of proteinuria detection include quantitative determination of the protein in a daily collection (to determine the severity of the disease process) and electrophoresis of urine proteins, enabling the determination of its causes. In the early stages of kidney disease, often in diabetic nephropathy, the amount of protein that passes into the urine is not sufficient to detect it on a general urine test. Then it is recommended to measure albumin in a 20-hour urine collection. Finding the level of this protein above 30 mg / l or above XNUMX mg / day enables the earliest detection of kidney damage. An alternative is the determination of the albumin / creatinine ratio in the morning urine sample (ACR).
Research supporting the diagnosis of kidney diseases
This group includes the testing of substances in the blood that should be cleared by the kidneys. One (but not the only) reason for the increase in serum levels is renal dysfunction. This group includes products of nitrogen metabolism – the aforementioned creatinine, as well as urea and uric acid. Significant impairment of kidney function may also be accompanied by acidosis (visible in blood gasometry) and an increase in the level of potassium in the blood.
Urinary tract infections
The urinary tract, especially in women, is prone to bacterial and fungal infections. Infection may be indicated by frequent and painful urination, and in infants and young children by fever. Confirmation of the infection can already be brought by a general urine test – the presence of bacteria, fungi and leukocytes, and sometimes also erythrocytes in the urine sediment. In the case of recurrent or non-susceptible infections, it is also necessary to perform urine culture with an antibiogram or mycogram – allowing for the precise identification of the infectious agent and its sensitivity to various groups of drugs.
Kidney stones
It is a disease that is often first manifested by sudden, sharp pain in the lumbar region caused by migrating mineral or organic deposits. It can be diagnosed by analyzing the urine for crystals present in the urine sediment and the daily excretion of certain components (including oxalates, citrates), as well as by chemical analysis of the excreted urinary stones.