Albumin in the urine
A study for microalbuminuria is used to screen for kidney lesions, in particular diabetic nephropathy, which significantly reduces costs and improves the prognosis of terminal CRF.
The frequency of diabetic nephropathy is 40-50% in patients with type 1 diabetes mellitus and 15-30% in patients with type 2 diabetes mellitus. The danger of this complication is that it develops slowly and gradually, therefore, for a long time it goes unnoticed. The earliest sign of diabetic nephropathy( before the appearance of proteinuria) is microalbuminuria. Microalbuminuria is the excretion of albumin in the urine, exceeding the permissible normal values, but not reaching the degree of proteinuria. Normally, no more than 30 mg of albumin is excreted per day, which is equivalent to a concentration of albumin in the urine of less than 20 mg / l in its one-time analysis. In proteinuria, the excretion of albumin with urine of exceeds 300 mg / day. Thus, the range of fluctuations in albumin concentration in urine with microalbuminuria is 30 to 300 mg / day or 20 to 200 μg / min. The appearance of a permanent microalbuminuria in a patient with diabetes mellitus testifies to the likely development( during the next 5-7 years) of a marked stage of diabetic nephropathy.
Another early marker of diabetic nephropathy is impaired intracellular hemodynamics( hyperfiltration, kidney hyperperfusion).Hyperfiltration is characterized by an increase in the glomerular filtration rate( GFR) above 140 ml / min. To determine GFR, a Reberg-Tareev test is used, based on a study of the clearance of endogenous creatinine.
A laboratory test characterizing the development of a pronounced stage of diabetic nephropathy is proteinuria( usually with unchanged urine sediment), a decrease in GFR, and an increase in azotemia( concentration of urea and creatinine in the blood serum).In 30% of patients develops a nephrotic syndrome( massive proteinuria - more than 3.5 g / day, hypoalbuminemia, hypercholesterolemia, edema).Since the onset of permanent proteinuria, the rate of decrease in GFR is on average 2 ml / min-month, which leads to the development of terminal CRF already 5-7 years after the detection of proteinuria.
At the stage of chronic renal failure, laboratory tests allow to determine the tactics of management of patients with diabetes mellitus.
With the development of CRF in patients with type 1 diabetes mellitus, the daily need for insulin sharply decreases, in connection with this the frequency of hypoglycemic conditions increases, which requires a reduction in the dose of insulin.
Patients with type 2 diabetes mellitus taking oral hypoglycemic drugs should be transferred to insulin therapy when developing chronic renal failure, since most of these drugs are metabolized and excreted by the kidneys.
When the serum creatinine concentration is more than 500 μmol / l( 5.5 mg%), it is necessary to consider the preparation of a patient for hemodialysis.
Serum creatinine concentrations of 600-700 μmol / L( 8-9 mg%) and glomerular filtration rate( GFR) of less than 10 ml / min are considered indications for kidney transplantation.
Increase in serum creatinine concentration to 10001200 μmol / l( 12-16 mg%) and a decrease in GFR of less than 10 ml / min is considered an indication for programmed hemodialysis.
Renal failure associated with diabetic nephropathy is the immediate cause of death in about half of cases of type 2 diabetes. It is very important for the clinician to conduct laboratory tests to monitor the dynamics of diabetic nephropathy.
According to the recommendation of WHO experts, in the absence of proteinuria, a study on microalbuminuria should be performed:
in patients with type 1 diabetes mellitus at least once a year after 5 years from the onset of the disease( if diabetes occurs after puberty) and at least 1 time inyear from the date of diagnosis of diabetes at the age of 12 years;
in patients with type 2 diabetes mellitus at least once a year from the time of diagnosis.
In normal excretion of albumin with urine, the fraction of glycosylated Hb( HbA1C) should be maintained at a level of no more than 6%.
In the presence of proteinuria in patients with diabetes mellitus, the rate of increase of proteinuria( in daily urine) and the rate of reduction of GFR are examined at least once every 4-6 months.
At present, the microalbuminuria test should be considered as an indicator of the evaluation of the function of plasma membranes of highly differentiated cells. Normally, negatively charged albumin does not pass through the glomerular kidney filter, primarily due to the presence of a high negative charge on the surface of the epithelial cells. This charge is due to the structure of phospholipids of cell membranes rich in polyene( polyunsaturated) fatty acids. The decrease in the number of double bonds in the acyl residues of phospholipids reduces the negative charge, and albumin begins to be filtered into the primary urine in an increased amount.
All these changes occur in the development of atherosclerosis, therefore microalbuminuria develops in patients with hereditary forms of HLP, coronary heart disease( CHD), arterial hypertension, as well as in 10% of practically healthy people( in screening studies) and in patients with impaired glucose tolerance. Changes in the structure of phospholipids of plasma membranes of highly differentiated cells occur in atherosclerosis and immediately affect the charge of membranes, so a study on microalbuminuria can reveal early stages of the disease.